B 8 .. .
FISH/FORESTRY INTERACTION PROGRAM
multidisciplinary research study initiated in 1981. The program wasstarted followingaseriesof This study was undertaken as part of the Fish/Forestry Interaction Program, a
major winter storms in 1978 that triggered landslides over much of the Oueen Charlotte Island forest land base. Originating on steep Slopes. manyslidesdeposited tonnes of debris in streams and on valley flats. The events raised private and public concerns over logging practices on the islands and prompted the establishment Of the 5 year program. Overall objectives of FFlP were:
0 to study the extent and severity of mass wasting and to assess its impacts on fish habitat and
0 to investigate the feasibility of rehabilitating stream and forest sites damaged by landslides. 0 to assess alternative silvicultural treatments for maintaining and improving slope stability. 0 to investigate the feasibility and success of using alternative logging methods, including
The program is jointly funded by direct appropriations from the Canada Department of Fisheries and Oceans, the B.C. Ministry of Forests (Research Branch), and the B.C. Ministry of Environment
estry Centre) and the Forest Engineering Research lnstituteof Canada (FERIC), Vancouver, B.C. (Fisheries Branch). Participating agencies include the Canadian Forestry Service (Pacific For-
Program results are published through the B.C. Ministry of Forests, Land Management Report
forest sites.
skylines, helicopters. and by logging planning. to reduce logging-related failures.
Series as well as papers presented at symposiums, conferences and through technical journals.
For information about the program contact Ministry of Forests, Research Branch, 1450 Gov- ernment Street, Victoria, B.C. V8W 3E7.
634.909711 B C ~ F RES LMR 41 c. I
SMITH, ROB. S O I L S . VEGETATION AND FORES T GROWTH ON LANOSLIDES AND
D-GROWTH AREAS nN THE QUEEN SURRCUNOING LOGGED AND OL
m
Soils, Vegetation, and Forest Growth on Landslides and Surrounding Logged and Old-growth Areas on the Queen
Charlotte Islands ~~ 23842-
by R.B. Smith, P.R. Commandeur
and M.W. Ryan
Canadian Forestry Service 506 West Burnside Road
Victoria, B.C. V8Z 1 M5
July 1986
Ministry of Forests
Canadian Cataloguing in Publication Data
Smith, R.B. (Richard Barrie), 1934-
surrounding logged and old-growth areas on the Queen Charlotte Islands.
Soils, vegetation, and forest growth on landslides and
(Land management report, ISSN 0702-9861 ; no. 41)
Bibliography: p. ISBN 0-7718-8522-9
1. Landslides - Environmental aspects - British Columbia - Queen Charlotte Islands. 2. Revegetation - British Columbia - Queen Charlotte Islands. 3. Forest productivity - British Columbia - Queen Charlotte Islands. 4. Trees - British Columbia - Queen Charlotte Islands - Growth. I . Commandeur, P.R. I I . Ryan, M.W. 111. British Columbia. Ministry of Forests. IV. Title. V. Series.
SD391 .S64 1986 631.6’4’0971 131 C86-092127-1
0 1986 Province of British Columbia
Published by the Information Services Branch Ministry of Forests Parliament Buildings Victoria, B.C. V8W 3E7
Copies of this and other Ministry of Forests titles are available from Queen’s Printer Publications, Parliament Buildings, Victoria, B.C. V8V 4R5.
ABSTHACJ
A synopt ic survey of 49 landsl ides ranging i n age from 1 t o 155 years was
conducted t o compare revegetat ion patterns and fo res t p roduc t i v i t y w i th
surrounding logged and old-growth stands. The l a n d s l i d e s l e f t a chaot ic mixture of logs , rocks, and so i l s o f var ied p ropor t ions , fu r ther compl ica ted
by add i t iona l mater ia ls eroded from t h e s l i d e edges f o l l o w i n g i n i t i a l f a i l u re . The upper po r t i on o f s l i des was p a r t i a l l y scoured t o bedrock or more
r a r e l y t o a compact g l a c i a l till, whereas the lower port ion mainly consisted
o f s l ide mater ia l deposi ted on or mixed with o r i g i n a l s o i l . E f f e c t i v e s o i l
depth on the upper two- th i rds o f the s l ides was s ign i f i can t l y l ess t han i n the
lower th i rd or i n the adjacent, non-slide surround. Bedrock exposure on
s l i d e s amounted t o 8, 10, and 2% f o r upper, middle, and lower slope posit ions,
respect ive ly , as compared with 1, 1, and 0% for non-sl ide terrain. For a l l
s l i d e s and s lope pos i t ions combined, exposed mineral s o i l and bare bedrock
averaged 88% a t 4 y e a r s a f t e r f a i l u r e and 14% a t 90 years. The reduct ion i n bare bedrock and m i n e r a l s o i l exposure occurred more r a p i d l y on lower than
middle or upper slopes. S o i l s on non-slide areas were c h i e f l y O r t h i c or Gleyed Ferro-Humic
Podzols. S o i l s on s l i d e s were severely perturbated but, i n add i t i on t o t he
Or th i c Regosols, many were recognized as Dys t r i c Brun iso ls and Gleyed and
Or th ic Ferro-Humic Podzols. Organic carbon contents in mid-s l ide so i l s were
h igh (avg. = 4 t o 8%). Vegetation development on these soils should be
considered as secondary rather than primary i n nature. Two major trends i n vegetative development on s l ide surfaces were
observed, one dominated by red a lder (A lnus " rubra )and one dominated by
coni fers . The former was most common on the lower por t ion o f s l ides ,
par t i cu la r ly those occur r ing i n low elevat ions on mater ia l der ived from
fine-textured bedrock or those with a re la t i ve ly h igh ca lc ium conten t .
Conifers tended to dominate on the middle and upper por t ions o f s l ides,
especia l ly i n h igh e leva t ions on re la t i ve ly coarse and a c i d s o i l m a t e r i a l .
I n i t i a l r e v e g e t a t i o n was dependent upon t h e a v a i l a b i l i t y o f stable mineral
s o i l m i c r o s i t e s and is lands o f debr is and other remnant organic mater ia l .
iii
Vegetation on s l i des was c l a s s i f i e d i n t o e i g h t groups and on logged areas i n t o
three groups based on dominant plants. The groups p a r t i c u l a r l y r e f l e c t e d
stages o f development, degree of red alder invasion, and type and s t a b i l i t y o f
substrate.
Revegetation i n logged areas differed from the ad jacent s l ides large ly as
a r e s u l t o f a higher component of western hemlock (Tsuga heterophyl la), lower
stocking o f red alder, and a greater proport ion of stable microsi tes. Logged
areas produced about 3 t imes the volume o f wood than s l ides i n the same (30- t o 59-year) age class. A lack of older logged stands i n the study precluded
d i r e c t comparisons a t l a t e r stages. However, based on appropr ia te y ie ld
tab les i t was estimated that the oldest group of slides, averaging 85 years of
age, haa produced about one-half the wood volume (con i fe r and red a lde r ) o f
normal second-growth stands of the same age.
i v
ACKNOMEDGEMEhTS
Personnel o f severa l fo res t companies arranged camp accommodation, gave
advice on lands l ide loca t ions and expedited the study i n various ways. These
incluaed Gary Marshall (CIPA), Ron Bronstein (Western Forest Products),
Steve Chatwin, Jer ry Johnson, Paul Chapman, and Jim Sears (MacMillan and
Bloedel) and Ron Frank and Gi lbert Brennenstuhl (Crown Forest Indust r ies) .
Jim Schwab, Dr. Howard Stauf fer , and Dave Wi l fo rd (B.C. Min is t ry o f Fores ts ) and K e i t h Moore (B.C. M i n i s t r y o f Environment) provided especial ly useful
technical advice. Bruce Thomson and Frances Noone (B .C. M i n i s t r y o f
Environment) helped iden t i f y rock samples. O r . W. Schof ie ld (UBC) i d e n t i f i e d
our d i f f i c u l t bryophytes and Drs. R. O g i l v i e and A. Ceska (Prov inc ia l Museum)
provided advice on other plant species. Or. Jim van Barneveld and L o r i Bishop
(B.C. M in i s t r y o f Environment) and Dr. Clarence Simmons (Canadian Forestry
Service) assistea i n analyzing our vegetation data. Their patience and
goodwi l l are much appreciated.
Assistance i n t h e f i e l d i n 1981 was ab ly led by Trudy Carson, aided by
Mary Morr is and Steve Mchaughton. Ed Wass (Canadian Forestry Service) great ly
assisted us on analyses o f data, soi ls, and wood samples.
Funding for the program has been provided through the Fish/Forestry
I n t e r a c t i o n Program covering equipment, t ranspor ta t ion , o ther f ie ld expenses,
and sa la r i es o f technica l personnel for 1981 and 1982. Salar ies o f
professional members o f the s tudy group fo r t he whole p e r i o d , f i e l d and other
expenses, and the sa la r i es o f technica l personnel for 1983 and beyond have been provided by the Canadian Forestry Service, Pacific Forestry Centre.
V
TABE OF COivTEivTS
ABSTRACT ............................................................. ACKNO.EDGEME.TS .....................................................
1 INTRUDUCTION .....................................................
2 STUDY DESIGN AND METHODOLOGY ..................................... 2.1 Descr ip t ion o f Var iab les ................................... 2.2 F i e l d Techniques ............................................
2.2.1 Transects ............................................ 2.2.2 Vegetation sampling .................................. 2.2.3 S o i l d e s c r i p t i o n .....................................
2.3 S o i l Analyses ............................................... 2.4 S t a t i s t i c a l Procedures .....................................
3 RESULTS .......................................................... 3.1 Surface Conditions o f S l i d e s and Adjacent Non-Slide
Surrounds ................................................... 3.2 Soi l Features ...............................................
3.2.1 Surface organic layer ................................ 3.2.2 M i n e r a l s o i l ......................................... 3.2.3 S o i l c l a s s i f i c a t i o n ..................................
3.3 Vegetation Development ...................................... 3.3.1 General vegetative cover ............................. 3.3.2 Deer browsing ........................................ 3.3.3 Tree stocking and composition by
number o f stems ...................................... 3.3.4 Tree composition by basal area ....................... 3.3.5 Vegetation groups ....................................
3.4 Forest Growth and S i te P roduc t i v i t y ......................... 3.4.1 Early height growth rates o f t rees ...................
3.4.3 Wood volume production ............................... 3.4.2 Basal area production ................................
iii V
1
3
3 7
7
9
10 11 11
12
12
20
20
20
29.
30 30
42
45
4a
49
64
64
65
68
v i
4 DISCUSS10 ......................................................... 73
5 SUMMARY ........................................................... 81
6 LITERATURE CITED .................................................. 83
APPENDICES
1
2
1
2
3
4
5
6
9
10
C h a r a c t e r i s t i c s o f f a i l u r e s and their surrounds ................... L i s t of plant species recorded.. ..................................
TALES
88
91
Slope, s o i l depth, and bedrock exposure by slope p o s i t i o n for s l i des and adjacent surround....................... ........... 15
Cover of n a t u r a l ( r o t t i n g ) l o g s and recent slash on s l i d e and surround surfaces ............................................. 15
Types o f organic surface horizons by age class of logged areas and for old-growth stands .......................................... 18
Types o f organic surface horizons by age c lass o f s l ides . . . . . . . . . . 19
Comparisons o f severa l charac ter is t i cs of surface organic horizons on s l i des ( S l i . ) with those on adjacent surrounds (Sur.). . . . . . . . . . 22
Mean p a r t i c l e s i z e d i s t r i b u t i o n o f the f rac t ion less than 2 mm on the basis o f rock type fo r mid-sl ide and undisturbed surround combined ................................................. 25
Mean pH for mid-slide and undisturbed mineral soi l on the basis o f rock type ................................................ 26
Mean percentages o f organic carbon and t o t a l n i t r o g e n and C:iu r a t i o s for mid-slide, logged and old-growth mineral soi l as subdivided by rock type ........................................... 28
Total vegetative cover f o r upper, middle, and lower slope pos i t ions for s l i de , logged, and old-growth plots.. . . . . . . . . . . . . . . . 33
Total cover o f vegetation, red alder, western hemlock, S i tka spruce, western redcedar, and a l l c o n i f e r s on s l i d e s f o r each associated rock type .............................................. 35
v i i
11
12
13
14
15
16
17
18
19
20
21
22
23
Total cover o f vegetation, red alder, western hemlock, S i t k a spruce, western redcedar, and a l l con i f e r s on logged areas for each associated rock type ..................................... Total cover o f vegetation, red alder, western hemlock, Sitka spruce, western redcedar, and a l l coni fe rs i n old-growth stands for each associated rock type ..................................... A comparison o f mean browse ratings f o r major t r ees , shrubs , and herbs for s l i de , logged, and old-growth stands ................ A comparison of mean browse ratings among species on s l i de , logged, and old-growth areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stocking of major tree species for sl ide, logged, and old-growth stands ................................................. Percentage composition of major t ree species for s l i de , logged, and old-growth stands based on number o f stems o f a l l s i z e s . ...... Percentage composition by basal area f o r major tree species for s l i d e , logged, and old-growth stands .......................... fvumber o f plots , average age, average total vegetative cover, and common plant species f o r vegetation groups, older logged p l o t s , and old-growth .................................................... Mean basal area for major tree species for s l i de and logged stands up t o 55 years of age. .............................. Basal area o f l i ve t r ee s for s l ide , logged, and old-growth stands by age class . . ............................................. Mean basal area of dead, standing trees fo r a l l s l i d e , logged, and old-growth p l o t s ...................................... Volumes o f l ive t rees for s l i de , logged, and old-growth stands by age c lass ...................................................... Comparison o f volumes o f t rees i n o ld s l i des (>60 yr) wi th those i n old-growth stands (>150 yr). ........................
37
38
43
44
46
46
49
51
66
67
69
70
71
v i i i
FIGURES
1 Loca t ion o f Queen Char lo t te I s lands o f f the coas t o f B r i t i s h Columbia. .................................................
2 A recent, open-slope, debr is avalanche..... ....................... 3 Use of border-tree increment cores as an a i d i n dat ing
landsl ides. A. Estimated year of sl ide (1958) fol lowed by per iod o f s low rad ia l growth. 6. Est imated year of s l ide (1963) fol lowed by p e r i o d o f r a p i d r a d i a l g r o w t h .................
4 Transect and vegetation plot sampling scheme on a debr is avalanche ................................................
5 Locat ions of landsl ide study areas on the Queen Charlot te Islands...........................................................
6 Percentage cover o f exposed s o i l and bedrock as a funct ion o f s l i d e age and s lope pos i t ion (U =Upper; M =Middle; L =Lower). R2: U =0.53; M =0.47; L =0.86. ..................................
7 Ac id i ty o f sur face o rgan ic layers as a f u n c t i o n o f s l i d e age (pH measured i n H$ and 0.01 M CaC12). R2: H$=0.27; CaC12 = 0.34 ...................................................
8 Organic carbon and to ta l n i t rogen concent ra t ions o f sur face organic layers as a f u n c t i o n o f s l i d e age. R2: Carbon=O. 65; ~ i t rogen=0.58 .....................................................
9 Percentage coarse fragments ( >2 mm) by v isual , volume estimate for mid-sl ide and undis turbed so i ls as a f u n c t i o n o f s o i l d e p t h .......
10 Percentage coarse fragments (2 mm t o ca. 20 mm) by weight o f c o l l e c t e d samples for mid-sl ide and undis turbed so i ls as a f u n c t i o n o f s o i l d e p t h ............................................
11 Percentage sand, s i l t , and c lay i n the m ine ra l so i l f r ac t i on ((2 mm) o f c o l l e c t e d samples for mid-s l ide and undis turbed so i ls as a f u n c t i o n o f s o i l d e p t h .......................................
12 Average pH (H20) for mid-s l ide and undis turbed minera l so i ls as a f u n c t i o n o f s o i l d e p t h ..........................................
13 Proport ions of podzols versus regosols with increasing t ime s ince lands l ide and a comparison with logged and old-growth surrounds ..............................................
14 Total vegetative cover on s l i des as a func t i on o f age and s lope pos i t ion (U =Upper; M =Middle; L =Lower). P lo t ted po in ts are averages o f stands within each age c lass ......................
2
4
6
8
14
17
21
21
23
23
24
27
30
31
i x
15
16
17
18
19
20
21
22
23
24
Total vegetative cover as a func t i on o f age fo r s l i des and logged areas. Plotted points are averages o f stands wi th in each age class.. .................................................. Average composition and s t ruc tu re o f s tands on s l i des 30-79 years o f age: A. Upper s lope, grani t ic , coarse conglomerate, and hard volcanic bedrock; E. Upper slope, fine sedimentary, calcareous, and so f t vo lcan ic bedrock; C. Lower s lope, grani t ic , coarse conglomerate, and hard volcanic bedrock; 0. Lower s lope, f ine sedimentary, calcareous, and sof t volcanic bedrock........ ........ Cover o f r e d a l d e r on s l i des as a f u n c t i o n o f s l i d e age and s lope pos i t ion. P lo t ted po ints are averages o f stands wi th in each age class. ................................................. Tota l cover o f con i fe rs on s l i des as a f u n c t i o n o f s l i d e age and s lope pos i t ion. P lo t ted po ints are averages o f stands within each age class..................................... ........ Average composition and s t ruc tu re o f s tands 30-59 years o f age: A. Upper s lope, s l ide; B. Upper slope, logged; C. Lower slope, s l i de ; D. Lower slope, logged ..................................... Bryophyte cover on s l i d e s (S I , logged areas (L) and i n old-growth stands ( O G ) as a func t i on o f age.. ................................ A 45-year-old s l i d e with a sparse s tock ing o f coni fers i n the upper port ion ( foreground) and a dense cover o f r e d a l d e r i n t h e lower por t ion ..................................................... Relationships among the e ight s l ide vegetat ion groups and old growth. G = Group ....................................... Early height growth of red alder, western hemlock, and S i t ka spruce i n s l i d e ( S ) and logged (L) areas. R2 for a l l regressions > 0 . 9 9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Average composition and s t ruc tu re o f s tands : A. Upper slope, s l i des >80 years o f age; B. Upper slope, old-growth; C. Lower s lope, s l ides X 0 years of age; 0. Lower slope, old-growth ........
32
36
39
39
40
41
47
54
65
72
X
1 INTRODUCTIOh
Landsl ides are a na tu ra l and common feature throughout much o f t h e
northwest coast o f N o r t h America (Swanston and Swanson 1976). However,
logging operat ions are known to increase the f requency of landsl ides
(Bourgeois 1978; S i d l e e t a l . 1985) and concern about the impact o f t h i s
accelerat ion on water and f i sh l e d t o t h e i n s t i t u t i o n o f t h e F i s h F o r e s t r y
I n t e r a c t i o n Program (Poul in 1985). This program concerns impacts of
lands l ides on f i sh hab i ta t s and f o r e s t s i t e s i n the Queen Char lo t te Is lands
(Fig. 1). This repo r t addresses the impact o f lands l ides on fo res t s i t es .
I n a d d i t i o n t o t h e i r p o t e n t i a l adverse e f f e c t s on f i sh hab i ta t , l ands l i des
may af fect forest product iv i ty through dest ruct ion o f estab l ished forest
stands, delays i n restocking, and decreased growth ra tes a f te r s tand
establishment. Improved knowledge o f p r o d u c t i v i t y e f f e c t s will a i d i n
p r e d i c t i n g r e a l i s t i c wood y i e l d s and ca lcu lat ion o f fu ture annual a l lowable
cu t ra tes i n areas susceptible t o mass wasting. Addit ional ly, knowledge o f
natural vegetative succession on mass-wasted areas i s bas ic to the p lanning
and implementation o f r e h a b i l i t a t i o n e f f o r t s , b o t h on s l i d e s and i n streams.
The spec i f i c ob jec t i ves o f t he s tudy were:
1. To study soi ls, vegetat ion, and forest growth on lands l ides
o f vary ing age and s i t e f ea tu res and i n adjacent logged areas and
old-growth stands.
2. To eluc idate s o i l and vegetation development on landsl ides
and logged areas. 3. To determine the product iv i ty of landsl ides for t ree growth i n
comparison with logged areas.
- 2 -
0 Q, d
I I
- 3 -
2 STUDY DESIGN AND METHODOLOGY
2.1 Descr ipt ion of Var iables
Forty-nine landsl ides, mainly open-slope debris avalanches (Swanston
1974), were selected for study (Fig. 2, Appendix 1). Sl ides selected
for study were main ly o f the open-slope var iety, a l though three V-notch,
deb r i s t o r ren ts were also included (Appendix 1). Se lec t i on o f s i t es t ook
i n t o account the fo l lowing var iables:
1. Bedrock Type. Eight bedrock formations described by Sutherland Brown
(1968) were encountered i n or adjacent t o t h e sample landsl ides.
Because most o f these have a d i v e r s e l i t h o l o g y , c l a s s i f i c a t i o n by
bearock type was based on col lected bedrock and s u r f i c i a l r o c k samples i n a d d i t i o n t o t h e mapped information. The rock types were
conso l ida ted in to seven categories:
a. Grani t ic (mainly Post- tectonic Plutons)
b. Conglomerate and Coarse Sandstone (mainly Honna formation) c. Soft Volcanics (mainly rhyol i tes and andesi tes o f the Masset and
Yakoun formations)
d. Hard Volcanics (mainly basalts o f t h e Karmutsen formation)
e. Calcareous (any type with m ine ra l s reac t i ng pos i t i ve l y t o
d i l u t e HC1)
f. Fine Sedimentary (mainly Kunga and Haida formations) g. Mixtures (more than one rock category but always inc lud ing a
Fine Sedimentary component).
L o c a t i o n s o f a l l s l i d e s a r e p l o t t e d on topographic maps and a e r i a l photographs i n the fo l lowing unpubl ished repor t on f i l e a t t h e P a c i f i c Forestry Centre, Victor ia, B.,C.: Smith, R.B., P.R. Commandeur, and M.W. Ryan. 1983 (Revised). Locations o f and bas ic data for lands l ides s tud ied dur ing forest growth invest igat ions (EP 862-2-7).
- 4 -
FIGURE 2. 4 recent, open-slope, debris avalanche.
- 5 -
2. Biogeocl imatic Zone. Within the Queen Char lo t te Is lands
Hemlock-Cedar-Spruce Subzone o f the Coasta l Western Hemlock Zone
(CWHg), s l i d e s were sampled i n the submontane var ian t (CWHg1) w i th
e leva t i ons t o about 350 m and the montane var ian t (CWHg2) ranging i n
elevation from about 350 t o 600 rn (Banner ” e t a l . 1986). S l ides were
a lso s tud ied i n the Coastal Cedars-Pine-Hemlock Zone (CCPH)
(Pojar 1983). One s l ide occurred i n a l o c a t i o n t r a n s i t i o n a l t o
the Mountain Hemlock (MH) Zone (Pojar 1983).
2
3. S l i de Age. Ages were taken f rom histor ical records or were estimated
by u t i l i z i n g a combination o f t h e age o f t he o ldes t pos t - s l i de t ree
sampled and the growth-r ing pat tern o f ad jacent t rees a f fected but
n o t k i l l e d b y t h e s l i d e (Terasmae 1975). Border-tree, increment
cores were studied with emphasis on growth r i ngs l a id down around the
t ime of establishment o f t he o ldes t s l i de t rees . The p o i n t o f any
abrupt change i n r i n g p a t t e r n o c c u r r i n g a t or before the date o f
establishment o f t h e o l d e s t s l i d e t r e e was deemed t o represent the
year o f t h e s l i d e ( F i g . 3). A sudden decrease i n r ing widths (F ig .
3A) might result from a loss o f a p o r t i o n o f t h e t r e e ’ s r o o t system
or an increase (Fig. 38) from a release from suppression. 4. Type o f Surrounding Vegetation. Two general types were recognized:
a. Old growth - from 150 t o ca. 1000 years o f age
b. Logged - from 1 t o 55 years since logging. 5. S u r f i c i a l M a t e r i a l . Major mater ia ls were co l luv ia l , mora ina l ,
organic, or some combination o f these.
6. Type o f Landslide. Landslides were i n i t i a l l y c a t e g o r i z e d
(Appendix 1) as i n Swanston (1974) as follows:
a. Debris slide. Rapid, downward movement o f unsaturated,
re la t i ve l y unconso l i da ted so i l and forest debr is.
b. Debris avalanche. Similar t o d e b r i s s l i d e b u t with a higher
s o i l water content and usua l ly with a greater runout zone.
The CCPH Zone has recent ly been assigned t o the CWH Zone as a subzone (pers. comm. from D. Meidinger, B.C. M in is t ry o f Fores ts ) .
- 6 -
C.
d.
e.
Debris flow. Rapid, downslope movement of water-saturated s o i l
and debr is by t rue f low processes. Often associated with debr is
avalanches and thus categorized with them.
Rotat ional slump. Downward and backward r o t a t i o n o f a s o i l
block with a minimum o f l a t e r a l movement.
Debris torrent. Debris f lows occurring i n well-defined drainage
channels, e.g., the bedrock-control led, V-notch gul l ies of
Schwab (1983).
I n subsequent data summaries the f i r s t f ou r ca tegor ies were combined and
only the debr is torrents t reated separately. Other than the rarely
encountered r o t a t i o n a l slump, a l l these types o f mass wast ing resul t i n
des t ruc t ion o f nearly a l l o f t h e o r i g i n a l v e g e t a t i o n ( F i g . 2).
FIGURE 3 . Use o f border-tree increment cores as an a i d i n dat ing landsl ides. A. Estimated year of s l i d e (1958) followed by per iod o f slow r a d i a l growth. 6. Estimated year of s l i d e (1963) followed by per iod o f r a p i d r a d i a l growth.
- 7 -
2.2 Field Techniques 2.2.1 Transects
To aid i n quantitative analysis of s i te factors associated wi th
s l i des and non-slide terrain, one or two transects were run across the slide i n each of the upper, middle, and lower t h i r d s a t a r i g h t angle t o t h e direction of the s l ide and 20 m into the unaffected forest (referred to hereafter as the "surround') on each s ide of the s l ide (Fig . 4 ) . A
to ta l o f 131 transects were surveyed, none on the three Kaisun s l ides (Appendix 1). A t in te rva ls of 3 to 10 m along each transect on the s l i d e and a t 3-m in tervals i n the surround, points were described as follows : 1. Soil depth (including humus) t o bedrock or an otherwise
impenetrable layer, measured by hammering a pointed steel probe into the ground w i t h a sledge hammer and recorded as over 1 m or, i f less than 1 m , as actual depth.
2. Surface organic layer depth including mixtures of mineral and organic particles (Ah layer ) , if present, as over 10 cm or under 10
cm . 3 . Surface organic layer type as mainly rot ten wood, mainly humified
material (FH), a mixture or layered combination of the two, mineral soil p l u s pedologically incorporated organic matter (Ah) , or l i t t e r only.
4. Mineral s o i l exposure type as undisturbed, gouge, or deposit. 5. Mineral s o i l exposure depth as shallow (<5 cm), deep (5-25 cm), or
very deep (>25 cm). 6. Mineral s o i l exposure cause, e.g., yarding, mass wasting, surface
erosion, and windthrow. 7. Slash as fine (<5 cm diameter) or coarse ( > 5 cm diameter). 8. Slope i n percent. 9. Aspect i n azimuth degrees. 10. Moisture regime as a qual i ta t ive assessment based mainly on soil
depth and texture, surface form, vegetation, and presence of sa tura ted so i l and c lass i f ied from dry t o wet as xeric (11, submesic ( 2 ) , mesic ( 3 ) , subhygric ( 4 ) , or hygric (5) (Pojar 1983).
- 0 -
\ SCOUR ZONE
B
C
DEPOSIT ZONE
FIGURE 4. Transect and vegetation plot sampling scheme on a debris avalanche.
- 9 -
11. Micro-re l ie f (sur face shape) as s t rong ly concave (O) ,
concave (l), s l i g h t l y concave (2), n e u t r a l ( 3 ) , s l i g h t l y
convex ( 4 ) , convex ( 5 ) , o r s t rong ly convex (6).
12. Other substrates, e.g., stump, roo t , bedrock, boulder 0 2 5 cm diameter), and stone (10-25 cm diameter).
Observations were recorded a t 1874 po in ts on s l ide sur faces and
a t 1773 po in ts on non-slide surfaces.
2.2.2 Vegetation sampling
On each t ransec t , a t l eas t one 4 x 4-m vegeta t ion p lo t was
establ ished i n t h e s l i d e (156 i n a l l ) and one i n the non-slide area
(122 i n a l l ) (Fig. 4) .
Vegetat ion descr ipt ion fo l lowed Walmsley ” e t a l . (1980).
Vegetation was assessed on the whole p l o t as fol lows: 1. Percentage cover f o r each vegetat ion layer and t o t a l cover o f
vegetat ion, bare mineral soi l , s lash, and ro t t i ng deb r i s .
2. Cover c lass i n percent and s p a t i a l d i s t r i b u t i o n , f o r a l l
species; and height c lass for trees, shrubs, and herbs (Walmsley
“ e t a l . 1980).
3. Browse u t i l i z a t i o n f o r herbs and shrubs as 0 (no u t i l i z a t i o n ) ,
1 (1-5% o f p l a n t browsed), 2 (6-25%), 3(26-50%), and 4 0 5 0 % ) (Walmsley ” e t a l . 1980).
Within a l l p l o t s d a t a on tree growth were co l l ec ted as fol lows:
1. For stands with t rees under 1.3 m height only, t rees were
counted by species and a range o f t ree he igh ts g iven . For each
species, two healthy, dominant or codominant sample t rees were
cu t and measured for to ta l he ight , annual he ight -growth
increments, and age. Basal discs were col lected f rom the cut
t rees for accurate age determination. I n logged stands, advance
and post-logging regeneration were separately noted when t h i s
was possible.
- 10 -
2. For stands with trees greater than 1.3 m he ight but less than
7.5 cm dbh (diameter a t 1.3 m height), data were co l l ec ted as
for (1) above except t h a t f o r a l l t r e e s g r e a t e r t h a n 1.3 m, indiv idual d iameters and heights were measured or estimated.
For each species, two healthy, dominant or codominant sample
t rees were c u t and t o t a l h e i g h t and up t o 10 recent
height-growth increments measured. Inc lud ing t rees less than
1.3 m height, over 400 t rees were c u t down and sampled i n t h i s
manner.
3. For stands with trees greater than 7.5 cm dbh, var iab le (wedge
pr ism) p lo ts (111 i n a l l ) centered on the vegetat ion p lo ts were
establ ished to co l lect mensurat ion data addi t ional to those
described i n (1) and (2). Increment borings and height
measurements were taken for two dominant or codominant t rees o f
each species. For trees within the p r ism p lo ts no t spec i f i ca l l y
measured, heights were estimated i n t h e f i e l d u s i n g t h e measured
t rees as guides. Tree volumes were computed using B.C. M in i s t r y
o f Forests volume equations (Watts 1983).
2.2.3 S o i l d e s c r i p t i o n
A t l e a s t one s o i l p i t was dug, described, and sampled i n the
undisturbed area adjacent to the sl ide and one i n the s l ide, both
about midway between the bottom and top o f t he f a i l u re . Desc r ip t i on
and sampling followed standard methods (Canada S o i l Survey Committee
1978; Walmsley e t a l . 1980). S o i l temperatures were taken i n f resh ly
exposed s o i l p i t w a l l s a t depths of 10 and 50 cm with a dial-head,
soi l -probe thermometer. Rock samples were co l lec ted from bedrock and
as loose rock f rom so i l p i t s .
- 11 -
2.3 S o i l Analyses
S o i l samples (366 i n a l l ) c o l l e c t e d from p i t s were subjected to
analyses as follows:
1.
2.
3.
4.
5 .
6 .
7.
Pa r t i c l e s i ze . Samples were dried, sieved, and the f ract ion over
2 mm weighed and expressed as a percentage o f t h e t o t a l sample weight. Texture o f t h e f i n e f r a c t i o n ((2 mm) o f se lec ted samples was
determined by the Bouyoucos hydrometer method (McKeague 1978).
Ac id i ty . The pH o f t h e f i n e s o i l f r a c t i o n was determined
po ten t iomet r ica l l y i n a 0.01 M CaC12 s o l u t i o n and i n H20
(McMullan 1971).
Color. Color o f t h e f i n e f r a c t i o n was determined i n both the moist
and dry states using Munsell Color Charts.
Organic carbon. Organic carbon content was determined for the
oven-dry, f i n e f r a c t i o n by the LECO Induc t ion Furnace Method (McKeague 1978).
Total n i t rogen. Total n i t rogen content was determined fo r t he oven-dry, f i n e f r a c t i o n by an automated, semi-micro K je ldah l method
(McKeague 1978). Ex t rac tab le i r on and aluminum. A procedure using sodium
pyrophosphate was used t o determine percent extractable iron and
aluminum on 84 samples (McKeague 1978).
Podzol test. A rap id t es t us ing sodium f l u o r i d e was conducted on 70
samples to d i f f e ren t i a te podzo l i c f rom o ther s o i l horizons (Brydon
and Day 1970).
2.4 S t a t i s t i c a l Procedures
Comparison o f s l i d e and surround surface s o i l c h a r a c t e r i s t i c s and
features o f vegetat ion within the var ious categor ies o f rock type, zone,
and age c lass were made u s i n g a v a r i e t y o f s t a t i s t i c a l procedures
inc lud ing mu l t ip le range tes ts and covariance analyses. To ad just for unequal ly rep l icated means i n Student-heuman-Keuls' and Duncan's m u l t i p l e
range tes ts , c r i t i ca l va lues were m u l t i p l i e d by a value that accounts for
- 12 -
t h e d i f f e r e n t number o f observations per treatment (Steel and To r r i e
1980). Linear regression analyses were performed t o determine trends with
t ime fo r s l i de and for surround parameters. For each group regression, an
F s t a t i s t i c and corresponding probabi l i ty , the regress ion coef f ic ients and
t s t a t i s t i c s , and p r o b a b i l i t i e s and a coef f i c ien t o f de termina t ion (R )
were produced. An analys is o f var iance was performed t o t e s t f o r
homogeneity o f regress ion coe f f i c ien ts across groups. A s i g n i f i c a n t
F ra t i o i nd i ca ted t ha t t he s lopes or i n t e r c e p t s o f t h e group regression
l i n e s d i f f e r e d beyond chance. S o i l temperature differences between s l i d e
and surround were tested us ing a paired-di f ference test (Mendenhall
1975). Differences were cons idered s ign i f i can t a t the 0.05 l e v e l ' i n a l l
analyses.
2
The d i ss im i la r i t y ana lys i s program COENOS (Jones 1978) o f t h e B.C.
M i n i s t r y o f Environment and a s i m i l a r i t y a n a l y s i s program available a t the
Pacif ic Forestry Centre (Stanek " e t a l . 1981) were used to he lp group vegetation types. Both programs employed a c luster ing procedure for
species presence or absence and plant cover data.
3 RESULTS
For ty-n ine s l ides and t h e i r surrounds were examined (Appendix 1, Fig. 5 ) .
One apparent s l ide (Deena-3, see Appendix 1) was l a t e r determined t o be the
r e s u l t o f yarding disturbance rather than mass wasting. Only data from i t s
surrouna were used i n subsequent analyses.
3.1 Surface Conditions of Slides and Adjacent Non-Slide Surrounds
The average open-face s l i d e was 454 (84-1072) m i n slope length, 59 (14-274) rn i n width, and the average area was 2.3 (0.1-15.5) ha. One
t o r r e n t r a n f o r more than 2400 m. I n g e n e r a l , t h e f a i l u r e s l e f t a
chaot ic, var ied mixture o f t ree bo les or logs, rocks, and s o i l .
Assuming an estimated average depth o f 1.5 m f o r s o i l s i n d i c a t e d by
probing as being over 1 rn deep, depths t o bedrock or t o a layer otherwise
- 13 -
impene t r ab le t o t h e probe were s i g n i f i c a n t l y less i n the upper and middle
t h i r d s of slides t h a n i n t h e l o w e r s l ide or any p a r t o f the surround (Table 1). No differences in average depth occurred between any of the s lope pos i t i ons i n t he su r round . S lope g rad ien t s decreased s i g n i f i c a n t l y from top t o bo t tom o f t h e slides and sur rounding te r ra in (Table 1). Both upper and middle s l ide segments were s i g n i f i c a n t l y s t e e p e r t h a n their equ iva len t su r round ing t e r r a in (Table 1). The mean gradien t o f the lower s l o p e o f slides i n t h e CWHg2 (montane var iant) was 46% as compared w i t h
29% f o r the CWHgl (submontane variant) and 31% f o r the CCPH zone. Unlike the CWHg1, there was no s i g n i f i c a n t d i f f e r e n c e between t h e g rad ien t o f
lower and middle t h i r d s (46 vs. 54%) i n t h e CWHg2. Bedrock exposure on t h e slides was s i g n i f i c a n t l y h i g h e r i n t h e middle and upper slope p o s i t i o n s t h a n i n the lower (Table 1).
The upper t h i r d o f slides was judged t o be more convex and drier than t h e middle and lower port ions b u t d i f f e r e n c e s were n o t s i g n i f i c a n t . The same p a t t e r n existed i n the non-slide surround. Logged t e r r a i n was rated as s i g n i f i c a n t l y more moist than s l i de su r faces .
The pe rcen tage o f ro t t i ng l ogs was s i g n i f i c a n t l y g r e a t e r i n old-growth s tands than in e i ther logged s tands or on slides (Table 2 ) .
Logged s t a n d s had a s i g n i f i c a n t l y h i g h e r r o t t i n g l o g c o v e r t h a n slides. A
g r e a t e r c o v e r o f r o t t i n g l o g s was p resen t on lower than upper slope p o s i t i o n s o f old-growth (21 vs. 13%), logged (11 vs. 4%) and s l ide (6 vs. 2%) surfaces. The cover o f rotting logs on slides generally
increased from 0 f o r the 1- t o 3-year class, t o 8% for the 30- t o 79-year class b u t decreased t o 6% f o r the >80-year class.
- 14 -
Rennell Sound
Phantom C r
Deena Rlver
Talunkwan Is.
FIGURE 5. Locations o f landslide study areas on the Queen Charlotte Islands.
- 15 -
TAELE 1. Slope, s o i l aepth, and bedrock exposure by slope posit ion for sl ides and adjacent surround
State Positions Slope So i l depth Bedrock exposure
S l i de
Surround
% cm %
U b68 a 50 b 8 a M 53 b 60 b 10 a L 33 d 92 a 2 b
U 50 b 93 a l b M 46 c 106 a l b L 32 d 110 a (1 b
a U=Upper ; M=Middle ; L=Lower . Means within columns fol lowed by the same l e t t e r a r e n o t s i g n i f i c a n t l y d i f f e r e n t a t t h e 0.05 l e v e l (Student-Newman-Keuls' M u l t i p l e Range Test 1.
TABLE 2. Cover o f n a t u r a l ( r o t t i n g ) l o g s and recent slash on s l i d e and surround surfaces
State Natura l ( ro t t i ng ) l ogs
Slasha Fine Coarse
Logged 8 b 8 a 22 a
S l i d e 4 c 2 b 8 b
Torrent o c O b 17 a
a Slash from recent logging, windthrow, or breakage. Fine = (5 cm diameter; coarse = >5 cm diameter.
Means within columns followed by the same le t te r a re no t s ign i f i can t l y d i f f e r e n t a t t h e 0.05 l e v e l (Student-Newman-Keuls' Mu l t i p le Range Test).
- 16 -
Slash cover was s ign i f i can t l y h ighe r i n logged stands than i n o l d growth
or on s l ides (Table 2). F ine (<5 cm diameter) slash decreased i n cover with
increasing age on bo th s l i de and logged areas. A s im i l a r re la t i onsh ip was
not c lear for coarse s lash except that the lowest cover occurred i n the
o ldest age c lasses fo r bo th s l ide and logged areas.
The surface cover of exposed m i n e r a l s o i l or bedrock decreased
exponent ia l ly with increasing age o f s l i des (F ig . 6 ) . The lower port ions of
t he s l i des accumulated an organic mat a t a r a t e s i g n i f i c a n t l y f a s t e r t h a n t h e
middle or upper port ions (Fig. 6) . Accumulat ion rates of surface organic
matter were r e l a t i v e l y low on slides associated with the coarse conglomerate
rock type and h igh on the f ine sedimentary type or mixtures o f t h i s with
other rock types.
Combining the 1- t o 3-year (two transects) with the 4- t o 14-year
(40 transects) age classes o f logged areas , the cover o f exposed s o i l and
bedrock averaged 14%. I n older logged stands s o i l exposure was about 5%, a
va lue s im i la r to tha t recorded fo r o ld g rowth (Tab le 3 ) . So i l exposure i n
recently logged stands was caused main ly by yard ing ac t i v i t ies and i n
old-growth stands by root overturns and surface runoff.
For s l ides, deep ( > l o cm) humus increased from 1% cover on those 1 t o 3
yea rs o ld t o 22% i n the over 80-year class (Table 4). This range compared
with an average o f 54% f o r logged areas with no trends with age and 62% i n
old-growth stands. Deep humus was predominant on logged and old-growth areas
and shallow humus was dominant on s l ides.
Logged surfaces had propor t ional ly a much h ighe r cove r o f ro t ten wood or mix tu res o f ro t ten wood and humif ied (FH) mater ia l than s l ides (Tables 3 and
4) . Par t i cu la r ly i n the o ldest age classes, sl ide surfaces were covered more o f ten with an H(Ah) layer , ind icat ing a greater degree o f m ix ing o f o rgan ic
and m ine ra l pa r t i c l es on sl ides (Tables 3 and 4). S l ides a lso had a
considerable port ion of their surfaces covered with a l e a f l i t t e r l y i n g
d i r e c t l y on minera l so i l . The percentage cover o f t h i s " l i t t e r o n l y '
category on sl ides reached a maximum i n the 15- t o 29-year c lass and was
present on ly rare ly i n the youngest and o ldest age classes (Table 4). The
percentage of o ther sur faces such as stumps, roots, and large s lash was
considerably greater on logged areas than on sl ides (Tables 3 and 4).
- 17 -
90
75
60
45
3 0
I5
M
35 70 IO5 I 4 0
Age of slide (years)
FIGURE 6. Percentage cover o f exposed s o i l and bedrock as a func t ion o f s l i d e age and s lope pos i t ion (U=Upper ; M=Middle; L=Lower) . Hz: U=0.53; M=0.47; L=0.86.
- 18 -
TABLE 3. Types o f organic surface horizons by age c lass of logged areas and for old-growth stands
Surfacea
Age Mean MSE Ht H- R+ R- Mix+ Mix- H(Ah)+ H(Ah)- L Other class age only surfaces
" " " " " " " _ % """""""""
1- 3 1 0 ab b25 ab 23 a 10 ab 10 a 20 a 3 a 0 a O a 3 a 6 a
4-14 8 15 a 25 b 15 a 11 ab 3 a 15 a 2 a 2 a 2 a l a 9 a
15-29 23 5 a 22 b 13 a 16 a 8 a 15 a 3 a 0 a O a l a 8 a
30-55 41 4 a 4 3 a 2 7 a 4 b O a 8 a 2 a O a l a l a 9 a
Old growth 6 a 42 a 21 a 5 b 3 a 14 a 1 a 1 a 2 a l a 4 a
a MSE = M i n e r a l s o i l or bedrock exposure; H = Humif ied mater ia l (FH); R = Rotten wood; Mix = Mixture o f H and R; H(Ah) = Organic matter with mineral s o i l incorporated; + = 710 cm th i ck ; - = <lo cm th i ck ; L = L i t t e r ; Other surfaces = Stumps, t ree boles, large s lash.
b Means within columns fol lowed by the same l e t t e r a r e n o t s i g n i f i c a n t l y d i f f e r e n t a t the 0.05 l e v e l (Student-Newman-Keuls' M u l t i p l e Range Test).
- 19 -
TABLE 4. Types of organic surface hor izons by age c l a s s o f s l i d e s
Surfacea
Age Mean MSE Ht H- R+ R- Mix+ Mix- H(Ah)+ H(Ah)- L Other c l a s s age only surfaces
" " " " " " " _ % """""""""
b 1 - 3 2 9 5 a I C I C O a l a O b < l a < l a l b O c l a
4-14 9 71 a 3 bc 8 c <1 a <1 a 1 ab 1 a 1 a 4 b 9 b 3 a
15-29 23 44 b 3 bc 21 b 0 a 3 a <1 ab 2 a 2 a 6 b 1 7 a 2 a
30-79 52 34 b 8 ab 18 b 2 a 2 a 1 ab <1 a 6 a 23 a 5 bc 2 a
BO+ 107 1 2 c 1 2 a 3 4 a < l a l a 4 a 2 a 6 a 2 7 a . I C 2 a
a MSE = M i n e r a l s o i l or bedrock exposed; H = Humif ied mater ia l (FH); R = Rotten wood; Mix = Mixture o f H and R; H(Ah) = Organic matter with minera l so i l incorpora ted ; + = > l o cm thick; - = <lo cm th ick ; L = L i t t e r ; Other surfaces = Stumps, t r e e boles, large slash.
b Means within columns fol lowed by the same l e t t e r a r e n o t s i g n i f i c a n t l y d i f f e r e n t a t t he 0.05 l e v e l (Student Newman-Keuls' M u l t i p l e Range Test).
- 20 -
3 . 2 Soil Features Unlike t h e transect survey which systematically sampled each of the
three slope positions of the slides and surrounds, data from the analyses of s o i l p i t s represent only the middle portions of slides and surrounds.
3.2.1 Surface organic layer Considering only those slides wi th a surface organic layer
su f f i c i en t ly d i s t i nc t t o allow collection of a clean sample, trends i n some properties occurred w i t h age and differences were noted between slide and surround (logged or old-growth). The pH of humus decreased s ignif icant ly and organic carbon and total n i t rogen contents increased significantly w i t h increasing s l ide age (Figs. 7
and 8). Significantly deeper layers of surface organic material occurred i n t h e surround than on slides (Table 5 ) . Values of pH for humus were significantly higher on slides than in the surround for 1- t o 29-year-old slides. Differences were not significant for older slides. The percentage of organic carbon was s ignif icant ly less for s l ide humus than i n the surround for 1- t o 29- and 30- t o 79-year-old slides. In contrast , the average carbon content of humus i n slides over 80 years of age was s imi la r to that i n the surround. Total nitrogen content was s ignif icant ly lower on slides i n the 1- t o 29-year age class , equal to the surround i n the 30- t o 79-year c lass and significantly higher for slides over 80 years of age. Ratios of C:N were generally lower on slides than surrounds but significantly so only for t h e 30- t o 79-year class (Table 5 ) .
Characterist ics of the surface organic horizons were not s ignif icant ly correlated w i t h the t y p e of associated rock or with biogeoclimatic zone.
3.2.2 Mineral s o i l Soi l s on slides were s ignif icant ly warmer i n the summer than
s o i l s i n logged and old-growth surrounds: 11.4 vs. 9.6OC a t 10 cm and 9.4 vs. 7.8OC a t 50 cm.
- 21 -
5 .0
4.5
4.0
PH 3.5
3.0
-.- 30 60 90 I20 I50
Age of slide (years)
FIGURE 7. Acidity of surface organic layers as a function of s l i de age (pH measured i n Hz0 and 0.01 M CaC12). R2: Hz0 =0.27; CaC12 = 0.34.
7 6 I I I I I I I I I
t i I I I I I I I ~ I
30 60 90 120 150
Age of slide (years)
FIGURE 8. Organic carbon and total nitrogen concentrations of surface organic layers a s a function o f s l i d e age. R2: Carbon =0.65; hitrogen = 0.58.
- 22 -
TABLE 5. Comparisons o f several characteristics of s u r f a c e on slides (S l i . wi th those on ad jacent sur rounds
organic horizons (Sur . )
Slide age Depth (cm) pH (H20) pH (CaC12) Organic C Total N c lass (yr) (%>
C:N r a t i o (%)
Sli. Sur. Sli. Sur. S l i . Sur. S l i . Sur. S l i . Sur. Sli. Sur. 1 - 29 a4 b 16 a 5.0 a 3.9 b 4.5 a 3.2 b 18 b 36 a 0.7 b 1.1 a 28 a 33 a
30 - 79 6 b 19 a 4.5 a 4.2 a 3.8 a 3.5 a 25 b 41 a 1.1 a 1.2 a 24 b 36 a
80+ 6 b 16 a 4.0 a 4.0 a 3.2 a 3.1 a 42 a 41 a 1.6 a 1.1 b 27 a 37 a
a Means wi th in age c l a s s / su r face o rgan ic ho r i zon characteristic pa i r ings fo l lowed by the same letter are n o t s i g n i f i c a n t l y d i f f e r e n t a t the 0.05 l eve l (S tuden t - Newman-Keuls I Multiple Range Test).
S o i l materials were g e n e r a l l y h i g h i n gravel (0.2-7.5 cm) and cobble (7.5-25.0 cm) con ten t wi th a few sites h i g h i n s t o n e s 025.0 cm). The average coarse f ragment conten t by volume as estimated v i s u a l l y on the s o i l p i t walls was 45% f o r slides and 39% for undis turbed surrounds. Differences between s l ide and surround were only marked i n the upper 30 cm o f the p r o f i l e s with slide s o i l s c o n t a i n i n g a b o u t 10% g r e a t e r volume of coa r se f r agmen t s i n t h a t por t ion than the undis turbed (Fig. 9). By weight, the average content of coarse f ragments less than about 2 cm diameter o f slide and undis turbed so i l s was 52 and 51%, r e spec t ive ly . Again, however, the s l ide so i l s exceeded t h e u n d i s t u r b e d s o i l s i n c o a r s e f ragment content by about 10% i n the upper 30 cm of the p r o f i l e s (Fig. 10).
Based on samples taken from hor izons loca ted a t depths ranging from the m i n e r a l s o i l s u r f a c e t o as deep as 110 cm, average particle size d i s t r i b u t i o n o f the f r a c t i o n <2 mm was 10.1, 25.5, and 64.4% f o r slides and 9.9, 26.4, and 63.9% fo r su r rounds fo r clay, s i l t , and sand, respectively. Al though e s sen t i a l ly no ave rage d i f f e rence ex i s t ed between
- 23 -
Coarse fragments by volume (%) 20 40 60
I I I I I I I
t - LOGGED AND OLD GROWTH SLIDE """
FIGURE 9 . Percentage coarse fragments (> 2 mm) by v isua l , volume estimate for mid-sl ide and undis turbed so i ls as a f u n c t i o n o f s o i l depth.
Coarse fragments by weight (%) 20 40 60
I 1 I 1 1 I I
LOGGED AND OLD GROWTH SLIDE """
FIGURE 10. Percentage coarse fragments (2 mm t o ca. 20 mm) by weight o f co l l ec ted samples for mid-s l ide and undis turbed so i ls as a f u n c t i o n o f s o i l depth.
- 24 -
s l i d e and adjacent surround, there were d i f f e r e n c e s i n p a r t i c l e s i z e
d i s t r i b u t i o n with depth (Fig. 11). S l i d e s o i l s had lower clay and
s i l t percentages and higher sand percentages i n the upper 30 em than
undisturbed soils. I n a less marked fashion, the reverse held below
30 cm.
Clay, silt and sand (%) 20 40 60 80
I 1 I I I I I 1
0 0
0.
0 0
: SAND
0 0 /yO 0
0 0
LOGGED AND OLD GROWTH SLIDE """
FIGURE 11. Percentage sand, s i l t , and c l a y i n t h e m i n e r a l s o i l f r a c t i o n ((2 mm) o f co l l ec ted samples for mid-slide and undis turbed so i ls as a funct ion o f s o i l depth.
- 25 -
Soi ls associated with f i n e sedimentary and calcareous rock types
were h igh i n clay content and those associated with g r a n i t i c and hard
volcanic bedrock were low i n clay (Table 6). Soi ls associated with
hard volcanics were s i g n i f i c a n t l y h i g h e r i n s i l t content than
g ran i t i c so i l s . So i l s assoc ia ted with f i n e sedimentary rock were low
i n sand content whereas those associated with g ran i te were h igh i n
sand. The s i l t / c l a y r a t i o was p a r t i c u l a r l y h i g h i n so i ls assoc iated
with hard volcanics and low i n s o i l s from coarse conglomerate and
calcareous rock types (Table 6).
TABLE 6 . Mean p a r t i c l e s i z e d i s t r i b u t i o n o f t h e f r a c t i o n less than 2 mm on t h e b a s i s o f rock type for mid-sl ide and undisturbed surround combined
ROC^ typea
F rac t i on GH cc HV sv CA FS MX
""""""" s/o " """"""
Clay b7.2 b 10.4 ab 7.2 b 9.9 ab 12.1 a 13.4 a 11.3 ab
Silt 22.9 b 26.5 ab 30.3 a 25.0 ab 23.8 ab 29.3 ab 27.9 ab
S a m 69.9 a 63.1 ab 62.5 ab 65.1 ab 64.1 ab 5 7 . 3 b 60.8 ah
Si l t /C lay 6.0 ab 2.8 c 6.6 a 3.4 abc 2.6 c 3.3 abc 3.3 abc
a L;R = Gran i t i c ; CC = Coarse conglomerate; HV = Hard volcanic; sv = Soft volcanic; CA = Calcareous; FS = Fine sedimentary; MX = Mixture.
Means within rows fol lowed by the same l e t t e r a r e n o t s i g n i f i c a n t l y d i f f e r e n t a t t h e 0.05 l e v e l (Student-hewman-Keuls' M u l t i p l e Range Test).
- 26 -
The average pH o f m i n e r a l s o i l was general ly greater i n s l i d e
s o i l s (avg. = 5.3) than i n the surround (avg. = 4.9) for the upper 60 cm o f t he p ro f i l es (F ig . 12). Soils associated with the coarse
conglomerate type were par t i cu la r ly ac id , espec ia l l y i n the
undisturbed state (Table 7). Contrary t o expectat ion, so i ls
associated with calcareous and f i n e sedimentary rock types and
mixtures were not any l ess ac id t han so i l s from g r a n i t i c s and
volcanics. Unlike surface organic horizons, the mineral s o i l showed
no d e f i n i t e t r e n d i n decreasing pH with increas ing s l ide age.
TABLE 7. Mean pH for mid-s l ide and undis turbed minera l so i l on the basis o f rock type
Rock typea
State GR cc HV sv CA FS MX
S l i d e b5.4 a 5.0 a 5.5 a 5.3 a 5.4 a 5.1 a 4.9 a
Undisturbed 5.2 a 4.4 b 5.1 a 4.9 a 4.9 a 4.8 ab 5.2 a
All 5.3 a 4.7 b 5.3 a 5.1 a 5.1 a 4.9 ab 5.1 ab
a GR = Grani t ic ; CC = Coarse conglomerate; HV = Hard volcanic; SV = Soft volcanic; CA = Calcareous; FS = Fine sedimentary; MX = Mixture.
Within rows, means fol lowed by the same l e t t e r a r e n o t s i g n i f i c a n t l y d i f f e r e n t a t t h e 0.05 l e v e l (Student-Newman-Keuls' M u l t i p l e Range Test).
- 27 -
Average percentages of organic carbon and t o t a l n i t r o g e n
decreased with depth from about 8 t o 5% f o r carbon and 0.4 t o 0.2%
f o r n i t rogen i n b o t h s l i d e and surround mineral soil. Percentages of
organic carbon for the logged surround were higher than for
old-growth and s l i d e except a t t h e extreme top and bottom o f t h e
sampled prof i les . N i t rogen content was general ly h igher for both
s l i d e and logged than for old-growth soils except a t t h e upper and
lower extremes o f t h e p r o f i l e s . R a t i o s o f C:N were lower throughout
most o f t he average p ro f i l e f o r s l i des t han f o r l ogged and old-growth
surrounds. The average C:N r a t i o o f o ld-growth mineral soi ls (29.9)
was s ign i f i can t ly h igher than fo r bo th logged (26.5) and s l i d e (24.1)
soils. Organic carbon content and C:N r a t i o were s ign i f i can t l y l ower
i n so i l s assoc ia ted with calcareous rock types than with some other
rock types (Table 8 ) .
- LOGGED AND OLD GROWTH """ SLIDE
FIGURE. 12 Average pH (H20) for mid-sl ide and undisturbed mineral soils as a f u n c t i o n o f s o i l depth.
- 28 -
High organic carbon contents occurred i n so i ls assoc iated with hard
volcanic and fine sedimentary rock types. The C:N r a t i o o f coarse
conglomerate s o i l s was s ign i f i can t ly h igher than fo r so i l s der ived
from a l l other rock types (Table 8).
TABLE 8. Mean percentages o f organic carbon and t o t a l n i t r o g e n and C:N r a t i o s for mid-slide, logged, and old-growth mineral s o i l as subdivided by rock type
State Rock typea
Property GR cc HV sv CA FS MX
" " " - " " " " " " " " _ S l i de % C b5 a 7 a 8 a 6 a 4 a 7 a 8 a
S l i de % N 0.2 a 0.2 a 0.3 a 0.2a 0.2 a 0.3 a 0.3 a
S l i de C:fu 22 b 32 a 23 b 24 b 22 b 25 b 22 b
Logged p lus old growth % C 8 ab 6 a b 8 a b 6 a b 4 b 1 0 a 6 ab
Logged p lus old growth % lu 0.3 a 0.2 a 0.3 a 0.2 a 0.2 a 0.3 a 0.2 a
Logged C:Eu 27 ab 33 a 23 ab 26 ab 24 ab 30 ab 21 b
Old growth C:N 29 b 43 a 28 b 29 b 20 b 36 ab 31 ab
All % C 6 ab 7 a b 8 a 6 a b 4 b 8 a 6 ab
All % N 0.2 a 0.2 a 0.3 a 0.2 a 0.2 a 0.3 a 0.3 a
All C:h 26 bc 34 a 24 bc 25 bc 22 c 29 b 24 bc
a GR = Gran i t i c ; CC = Coarse conglomerate; HV = Hard volcanic; SV = S o f t volcanic; CA = Calcareous; FS = Fine sedimentary; MX = Mixture.
b Within rows, means followed by the same l e t t e r a re no t s ign i f i can t ly d i f f e r e n t a t t h e 0.05 l e v e l (Student-kewman-Keuls' M u l t i p l e Range Test).
- 29 -
3.2.3 S o i l c l a s s i f i c a t i o n The predominant s o i l group i n logged and old-growth stands was
the Ferro-Humic Podzol (U.S. c l a s s i f i c a t i o n = Humic Cryorthod) within
which 65% o f t h e p r o f i l e s were c lass i f i ed . O f t h i s , 74% were i n the
Or th i c subgroup, 23% i n the gleyed subgroup, and one p r o f i l e was a
P lac i c Ferro-Humic Podzol. The second most common s o i l group was the
Humo-Ferric Podzol (Typic Cryorthod) within which 25% o f t h e p r o f i l e s
were c l a s s i f i e d (50% Gleyed and 50% Orthic). The remainder were
Humic Podzols (Humods), Dystr ic Brunisols (Dystrochrepts) , and F o l i s o l s ( F o l i s t s ) . As ind ica ted by bur ied H horizons, about 15% o f
t h e p r o f i l e s i n logged and old-growth stands included prof i les
al tered by previous mass wasting events.
Because o f t h e extreme pe r tu rba t i on , so i l s on s l i d e s were
extremely varied i n morphology, r e s u l t i n g i n 28 separate
c lass i f i ca t i ons o r comb ina t ions o f c lass i f i ca t i ons a t t he subgroup
leve l . O f t he 44 s l i d e p r o f i l e s sampled, 15 involved t runcated and
bur ied (avg. depth o f b u r i a l = 28 cm) pre-mass wast ing so i l s and
p r o f i l e s with post-mass wasting erosional overlays (avg. = 12 cm
deep). I n addi t ion, bur ied H horizons were noted within the pre-mass
wast ing por t ion o f two prof i les . Despi te the per turbat ion, on ly 23%
o f t h e s l i d e p r o f i l e s were c l a s s i f i e d i n the Regosol group (Ent iso ls )
with the remainder largely composed o f perturbated Podzols (64%) and Dys t r i c Brun iso ls (9%). O f the Podzols, the Ferro-Humic Podzols
dominated (57%), Humo-Ferric Podzols were second most common ( 3 2 % ) , and the remainder were Humic Podzols.
With increasing age c lass o f s l i de , t he p ropor t i on o f Podzols
increased and t h a t o f Regosols decreased (Fig. 13). Regosols d i d n o t
occur i n the o ldes t age class o f s l i d e s or i n the logged and
old-growth stands.
- 30 -
3.3 Vegetation Development
3.3.1 General vegetative cover
Over 180 plant species .were recorded (Appendix 2). The average
to ta l vegetat ive cover on a l l s l i d e s was 48%. Higher average covers occurred i n the lower s lope posi t ion than the upper (Fig. 14). To ta l
vegetative cover averaged 63% on logged areas and 81% i n old-growth
stands with no s ign i f i can t d i f fe rences among slope posi t ions (Table 9). Logged areas had more vegetative cover than slide areas
o f s i m i l a r age (Fig. 15). A t 40 years of age, for instance, the
average vegetative cover was 64% on s l i d e s and 94% on logged areas.
I00
80
60
%
40
20
4 PODZOLS
- 0 REGOSOLS ... ..
.. - 1 ... ... ... ... ... ... ... . . .. ...
n .... ....
1-3 4-14 15-29 30-79 80+ OLD GROWTH
Age class of slides AND LOGGED
FIGURE 13. Proportions o f podzols versus regosols with increasing t ime since lands l ide and a comparison with logged and old-growth surrounds.
- 31 -
100
80 h
8 5 v
60 0 a, > a a, a 40 a, > a
.- c,
c,
- c,
r-0 20
Age of slide (years)
D I I I I 1 I I 1 1 I
20 40 60 80 I00
FIGURE 14. Total vegetative cover on s l i des as a f u n c t i o n o f age and slope p o s i t i o n (&Upper; WMiddle; I= Lower). P lo t ted po in ts a re averages of stands within each age class.
- 32 -
I O 0
80
60
40
20
- I 0
- 0 i ii /
SLIDE
0 OLD GROWTH
I I I I I A
20 40 60 80 I00
Age (years)
FIGURE 15. Total vegetative cover as a function of age for s l ides and logged areas. Plotted po in t s are averages of stands w i t h i n each age class .
- 33 -
TABLE 9 . Total vegetative cover for upper, middle, and lower slope pos i t ions fo r s l ide , logged, and old-growth p lots
State Slope p o s i t i o n S l i d e Logged Old growth
- " " " % " """- Upper a37 b 63 a 80 a
Middle 49 ab 64 a 82 a
Lower 63 a 62 a 82 a
a Within columns, means fol lowed by the same l e t t e r a r e n o t s i g n i f i c a n t l y d i f f e r e n t a t t h e 0.05 l e v e l (Student-Newman-Keuls' M u l t i p l e Range Test).
- 34 -
Using covariance analyses t o account f o r d i f ferences i n average
s l i d e ages within rock types, the highest vegetative cover occurred
on sl ides associated with f i n e sedimentary, calcareous, and mixture
rock types and the lowest with coarse conglomerate and hard volcanic
types (Table 10). S i g n i f i c a n t l y lower cover o f red a lder (A lnus - rubra) on sl ides occurred i n associat ion with coarse conglomerate and
hard volcanic rock types than with calcareous, fine sedimentary, and
mixture types. Western hemlock (Tsuga heterophyl la) preferred
grani t ic-associated s l ides, whereas Sitka spruce (Picea si tchensis)
had s ign i f icant ly greater cover on sl ides associated with the fine
sedimentary rock type (Table 10, Fig. 16).
Expressing cover values as r a t i o s o f one species t o another gave
add i t i ona l i ns igh ts t o t he s o i l preferences o f deciduous and coniferous t r e e species. On th is basis, rock types f e l l i n t o two
groups. One composed o f granitic, coarse conglomerate, and hard
volcanic types had a1der:conifer cover rat ios ranging from 0.1 t o 0.3, a1der:hemlock r a t i o s from 0.2 t o 0.8, and S i t ka spruce:hemlock
r a t i o s from 0.4 t o 1.3. The other group (so.ft volcanic, calcareous,
f i n e sedimentary, and mixtures) had cons is ten t ly h igher ra t ios :
a1der:conifer (range 0.8 t o 1.8); a1der:hemlock (range 2.4 t o 12.2);
and Sitka spruce : hemlock ( range 1.6-5.4).
The relat ionships noted between cover and rock type on s l i d e s
were not as evident on logged areas (Table ll), and i n old-growth
stands they were rare (Table 12). Logged stands associated with f i n e
sedimentary rock had an especial ly high cover of red alder and low
con i fe r cover. High conifer cover on logged areas was associated
with coarse conglomerate rock and high western redcedar cover with
hard volcanics (Table 11).
- 35 -
TABLE 10. Total cover of vegetation, red alder, western hemlock, S i t ka spruce, western redcedar, and a l l c o n i f e r s on s l i d e s f o r each associated rock type
Cover Rock typea
Gf3 cc HV sv CA FS MX
""""""" % " " " " " _ Tota l vegetat ion b47 bc 32 c 39 c 45 bc 61 a 60 a 64 ab
Red a lder 5 bc 2 c 4 c 16 ab 22 a 24 a 25 a
Western hemlock 21 a 8 b 5 b 2 b 2 b 1 0 b 6 b
Sitka spruce 8 b 7 b 6 b O b 1 0 b 2 2 a 9 b
Western redcedar 3 a l a 2 a 2 a < l a O a l a
Tota l con i fe rC 34 a 16 c 14 c 13 c 12 c 32 ab 20 bc
a GR = Gran i t i c ; CC = Coarse conglomerate; HV = Hard volcanic; SV = Soft volcanic; CA = Calcareous; FS = Fine sedimentary; MX = Mixture.
Means are adjusted using age as a covariant. Within rows, means fol lowed by the same l e t t e r are n o t s i g n i f i c a n t l y d i f f e r e n t a t t h e 0.05 l e v e l ( t - t e s t matrix).
c Includes minor species.
- 36 -
I A
20
30 L fn m 20
10
RED ALDER 'p H E M L O i K WESTERN 9 SITKA WESTERN
'9 SPRUCE ,/f R E D C E i R
f
YELLOW LODGEPOLE PINE
m 2 0 30 I
1
40 I" 30
m
20
10
FIGURE 16. Average composition and s t ruc tu re o f stands on s l i des 30-79 years o f age: A. Upper slope, granitic, coarse conglomerate, and hard volcanic bedrock; B. Upper slope, fine sedimentary, calcareous, and soft volcanic bedrock; C. Lower slope, granit ic, coarse conglomerate, and hard volcanic bedrock; D. Lower slope, f ine sedimentary, calcareous, and soft volcanic bedrock.
- 37 -
The re la t ionsh ip o f red a lder cover with age o f s l i d e s d i f f e r e d
markedly from tha t o f con i fe rs (F igs . 17 and 18). Alder cover
apparent ly increased rap id ly to age 25, decreased sharply t o age 50,
and then decreased only s l ight ly to 100 years (Fig. 17). I n cont ras t , con i fe r cover inc reased f rom s l ide in i t ia t ion to 100 years
(Fig. 18). Total alder cover was highest i n the lower slope
posi t ion, intermediate i n the middle, and l e a s t i n the upper slope
pos i t ion, whereas con i fe r cove r d id no t d i f f e r among slope posi t ions
(Figs. 17, 18, and 19A, B). I n logged sites, red alder cover was
high only i n the lower slope posit ion, but i t s o v e r a l l average cover
d i d n o t d i f f e r s i g n i f i c a n t l y between logged and s l i d e areas (Fig. 19 C, D) .
TABLE 11. Total cover of vegetation, red alder, western hemlock, S i t ka spruce, western redcedar, and a l l c o n i f e r s on logged areas for each associated rock type
Cover Rock typea
GR cc HV sv CA FS MX
""""""" % " " " " " _ Tota l vegetat ion b70 ab 65 ab 42 b 56 b 63 ab 90 a 59 ab
Red a lder 14 b I C 2 b c IC IC 5 1 a 1 b c
Western hemlock 28 ab 35 a 9 b 14 b 24 ab 7 b 34 ab
Si tka spruce 4 a 9 a 6 a 9 a a a 5 a 2 a
Western redcedar 3 b l b 1 2 a l b l b 2 b O b
Tota l con i fe rC 35 ab 46 a 27 ab 23 b 33 ab 13 b 36 ab
a GR = Grani t ic ; CC = Coarse conglomerate; HV = Hard volcanic; SV = Soft volcanic, CA = Calcareous; FS = Fine sedimentary; MX = Mixture.
Means are adjusted using age as a covariant. Within rows, means fol lowed by the same l e t t e r a r e n o t s i g n i f i c a n t l y d i f f e r e n t a t t h e 0.05 l e v e l ( t - tes t mat r i x ) .
Includes minor species.
- 38 -
TABLE 12. Total cover of vegetat ion, red a lder, western hemlock, S i t ka spruce, western redcedar, and a l l c o n i f e r s i n old-growth stands for each associated rock type
Cover Rock typea
GR cc HV sv CA FS MX ~ ~~
""""""" % " " " " " _ Tota l vegetat ion b81 a 77 a 73 a 86 a 79 a 82 a 84 a
Red a lder O a (1 a 2 a l a O a < l a < l a
Western hemlock 43 a 52 a 29 a 37 a 45 a 45 a 25 a
Sitka spruce 19 a O a 5 a 8 a 7 a l a 4 a
Western redcedar 5 a 6 a 8 a 1 2 a 5 a 1 7 a 4 a
Yellow cypress l a 5 a b l b 3 a b O b 2 a b 9 a
Tota l con i fe rC 68 a 60 a 45 a 60 a 57 a 65 a 45 a
a GR = Gran i t i c ; CC = Coarse conglomerate; HV = Hard volcanic; SV = Soft volcanic; CA = Calcareous; FS = Fine sedimentary; MX = Mixture.
Means are adjusted using age as a covariant. Within rows, means fol lowed by the same l e t t e r a r e n o t s i g n i f i c a n t l y d i f f e r e n t a t t h e 0.05 l e v e l ( t= tes t mat r i x ) .
C Includes minor species.
- 39 -
0 SLOPE POSITION ""_ UPPER - - MIDDLE
- 40
8 kl
P E m
U
'0"".
20 4 0 60 80 I00
Slide age (years)
FIGURE 17. Cover o f red a l d e r on slides as a func t ion o f slide age and slope pos i t i on . P lo t t ed po in t s are averages o f stands within each age c l a s s .
60
20 4 0 60 80 I00
Slide age (years)
FIGURE 18. Tota l cover o f coni fe rs on slides a s a funct ion of s l ide age and s l o p e p o s i t i o n . P l o t t e d p o i n t s are averages of stands within each age class.
- 40 -
20
m
IO
A
C
RED ALDER 'f HEMLOiK WESTERN 9 1
SITKA SPRUCE f WESTERN REDCEfR
7 YELLOW LODGEPOLE
CYPRESS c t f PINE
A
B
2o t A
D
20 m IO
FIGURE 19. Average composition and s t ruc tu re o f stands 30-59 years o f age: A. Upper s lope, s l ide; B. Upper slope, logged; C. Lower slope, s l i de ; D. Lower slope, logged.
- 41 -
Shrub cover was genera l ly low but was s i g n i f i c a n t l y h i g h e r on logged areas (9%) than on slides (3%), and was in te rmedia te ( 5 % ) i n old growth. Herb c o v e r , a l s o low, averaged 9% i n old-growth stands and 8% in l ogged and s l i de areas. Up t o 55 years o f age, logged s t a n d s had higher bryophyte cover than slides, but cover on t h e l a t te r subsequent ly increased rapidly w i t h age c lass (Fig. 20). On slides over 80 years of age, average bryophyte cover exceeded that in old-growth stands (Fig. 20). For s tands younger than 56 years ( t h e maximum age of sampled logged s tands) , the average bryophyte cover was s i g n i f i c a n t l y h i g h e r f o r logged s tands (26%) than f o r slides
(12%)
80
- S
L
C L ;n ...
L i[l ... ... ... ... ... ... ... ... ...
L 1~ ......
... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ...
... ... ... ... ... ... ... ... ... ... ... ...
... .. s i:::::: ... .... ...
1-3 4-14 15-29 30-79 80+ OG
Age class
FIGURE 20. Bryophyte cover on slides ( S ) , logged areas (L) and i n old-growth s t a n d s ( O G ) as a func t ion o f age.
- 42 -
3.3.2 Deer browsing
Introduced Sitka deer (Odocoileus hemionus s i t kens i s Merriam)
are found on a l l major islands i n the Queen Charlottes (Cowan 1956)
and are now numerous. Consequently, browsing of shrubs, herbs, and
tree regenerat ion can be severe (Pojar and Banner 1984). Browse u t i l i z a t i o n d a t a were analyzed only for trees and shrubs
less than 2 m i n height , those avai lab le to deer , and only fo r those
s u f f i c i e n t l y f r e q u e n t t o a l l o w v a l i d comparisons.
Western hemlock was browsed s i g n i f i c a n t l y more on s l i d e s and
logged areas and Sitka spruce more on s l ides than under old-growth
stands (Table 13). Yellow cypress (Chamaecyparis nootkatensis) was
browsed more heav i l y on s l ides than i n logged areas or old-growth
stands. Red a lder and western redcedar (Thuja plicata) showed no
s igni f icant browse u t i l i z a t i o n d i f fe rences among states. Salmonberry
(Rubus spec tab i l i s ) was browsed s i g n i f i c a n t l y more on s l i d e s and
logged areas than i n old growth (Table 13). No other d i f ferences
among s ta tes were ev ident for o ther shrubs. O f herbs, only deer fern
(Blechnum spicant) and sword fern (Polyst ichum munitum) were
su f f i c i en t l y f requen t for comparisons between states. Deer f e r n was
browsed s i g n i f i c a n t l y more on s l i des and sword f e r n m r e i n logged
areas than i n o l d growth (Table 13).
On slides, western redcedar was browsed s i g n i f i c a n t l y more than
western hemlock, S i t k a spruce, and red alder (Table 14) . Red a lder
was browsed s ign i f i can t ly less than the o ther th ree spec ies tes ted .
O f the shrubs, huckleberries (Vaccinium spp. ) were browsed
s i g n i f i c a n t l y more than false azalea (Menziesia ferruginea). O f t he
herbs tested, wood-rush (Luzula parv i f lora) was browsed s i g n i f i c a n t l y
l e s s t h a n a l l o t h e r s . Deer fe rn was browsed s i g n i f i c a n t l y more than
lady- fern (Athyr ium f i l ix - femina ssp. cyclosorum) and Merten's sedge
(Carex mertensii) (Table 14).
On logged areas, western redcedar was s i g n i f i c a n t l y more browsed
than Sitka spruce and western hemlock. No differences occurred among
the shrubs tested and deer fern and sword f e r n were more severely
browsed than lady-fern and Merten's sedge (Table 14) .
- 43 -
TABLE 13, A comparison of mean browse ratings for major t rees , shrubs , and herbs for slide, logged, and old-growth stands
State Treesa Shrubsa Herbsa Dr Hw Ss Cw Cy Rs Vspp M f 0s Pm
Slide b0.8 a 1.4 a 1.4 a 2.4 a 3.5 a 2.7 a 2.7 a 2.0 a 1.6 a 1.3 ab
Logged 1.0 a 1.3 a l . l ab 2.3 a 1.2 b 2.9 a 3.0 a 2.8 a 1.3 ab 1.7 a
Old growth 0.0 a 0.8 b 0.8 b 1.8 a 0.5 b 1.9 b 2.7 a 2.2 a 1.0 b 0.8 b
a Or = Red alder; Hw = Western hemlock; Ss = Sitka spruce; Cw = Western redcedar; Cy = Yellow cypress; Rs = Salmonberry; Vspp = Huckleberry species (Vaccinium parvifolium, V. ovalifolium and V. alaskaense combined); Mf = False azalea; Bs = Deer fern; Pm = Sword fern.
-
b Within columns, means followed by the same l e t t e r are not significantly d i f f e ren t a t t he 0.05 level (Duncan's Multiple Range Test).
- 44 -
TABLE 14. A comparison o f mean browse r a t i n g s among species on s l ide , logged, and old-growth areas
Species Slide Logged Old growth
Group Ratinga 1 2 Ratinga 1 2 Ratinga 1 2
Red alder Tree Western hemlock Sitka spruce Western redcedar
False azalea Shrub Salmonberry Red elderberry Huckleberry spp.
Lady f e r n Herb Deer f e r n Merten's sedge Wood-rush Sword f e r n
0.8 1.4 1.4 2.4
2.0 2.7 2.0 2.7
0.9 1.6 0.9 0.4 1.3
c de b cd b cd a ab
b bc ab a ab abc a a
b de a c b de c e ab cd
" "
1.3 b cd 1.1 b de 2.3 a b
2.8 a a 2.9 a a
3.0 a a " "
0.7 b e 1.3 a cd
0.2 b f 1.7 a c
" "
0.8 0.8 "
"
1.0 "
"
0.8
"
a c a c
a b "
"
a a
"
a c "
"
a c
i
a 1 = Within columns and groups, means followed by the same l e t t e r a r e n o t s i g n i f i c a n t l y d i f f e r e n t a t t h e 0.05 l e v e l (Duncan's M u l t i p l e Range Test).
2 = Within whole columns, means fol lowed by the same l e t t e r a r e n o t s i g n i f i c a n t l y d i f f e r e n t a t t h e 0.05 l e v e l (Duncan's M u l t i p l e Range Test).
- 45 -
I n old-growth stands there were no d i f ferences i n browse l e v e l s
within groups o f t rees , shrubs, and herbs but i n a comparison o f a l l six species the two shrubs, false azalea and huckleberry, were
s i g n i f i c a n t l y more browsed than the two t r e e and two herb species.
3.3.3 Tree stocking and composition by number of stems
Average stocking o f t ree regenerat ion i n logged and s l ide s tands
was su f f i c ien t bu t var iab le (Tab le 15). Western hemlock predominated
i n a l l ' t h r e e s t a t e s and western redcedar was r e l a t i v e l y numerous on
sl ides (Table 15). The average number o f r e d a l d e r stems was much
less i n the upper t h i r d o f s l i d e s (700 per hectare) (Fig. 21) and
logged surrounds (0 per hectare) than the middle (3300 per hectare)
or lower th i rds (4200 per hec tare) o f s l ides and the middle (1500 per
hectare) or lower (1400 per hectare) thirds of logged stands. Western hemlock, the most common o f t h e t r e e species, was over twice
as numerous i n the upper t h i r d o f b o t h s l i d e s and logged areas than
i n the middle or lower th i rds. Red a lder stems were 13 times more
numerous on sl ides associated with calcareous rock types than on
those associated with grani t ic rock types. Western hemlock stems
were over 3 times as numerous on sl ides associated with g r a n i t i c as
those associated with calcareous rock.
The percentage composition o f red a lde r , based on stems per
hectare, was strongly associated with severely disturbed areas, i .e.,
s l ides (Table 16). Conversely, the western hemlock component was
s ign i f i can t l y g rea te r i n old-growth and logged stands than on s l i des
(Table 16). Sl ides a lso featured high components o f S i t k a spruce and
western redcedar r e l a t i v e t o logged and old-growth stands (Table 16). When percentage composition was compared f o r t r e e
species among slope posi t ions and between logged and s l i d e p l o t s ,
s ign i f icant d i f ferences occurred for western hemlock only. For t h i s
species, percentage composition was s ign i f i can t ly h igher fo r logged
stands than for s l i d e s f o r each slope posi t ion. For s l ides, the
percentage composition o f western hemlock was s ign i f i can t ly h igher i n
the upper slope position than i n the middle or lower posit ions.
- 46 -
TABLE 15. Stocking of major tree species for sl ide, logged, and old-growth stands
State Speciesa
Or Hw ss cw CY
""""" Stems/hab- - - - - - - - - - S l i d e c3472 a 16116 b 4904 a 8394 a 1308 a
Logged 1069 b 20591 b 2966 a 1636 b 206 a
Old growth 12 b 70254 a 5939 a 3792 b 1053 a
a D r = Red alder; Hw = Western hemlock; Ss = S i t ka spruce; Cw = Western
b AU sizes. C Within columns, means fol lowed by the same l e t t e r a r e n o t s i g n i f i c a n t l y
redcedar; Cy = Yellow cypress.
d i f f e r e n t a t t h e 0.05 l e v e l (Student-Newman-Keuls' Mu l t i p le Range Test).
TABLE 16. Percentage composition o f major t ree species for s l ide , logged, and old-growth stands based on number o f stems o f a l l s i z e s
State Speciesa
Dr Hw ss cw CY
S l i de b16 a 37 b 18 a 24 a 3 a
Logged 7 b 71 a 13 ab 7 b l a
Old growth (1 b 77 a 9 b 8 b 3 a
a D r = Red a lder ; Hw = Western hemlock; Ss = S i t ka spruce; Cw = Western
b Within columns, means fol lowed by the same l e t t e r a r e n o t s i g n i f i c a n t l y redcedar; Cy = Yellow cypress.
d i f f e r e n t a t t h e 0.05 l e v e l (Student-Newman-Keuls' Mu l t i p le Range Test).
,
- 47 -
FIGURE 21. A 45-year-old s l i d e with a sparse stocking of coni fers i n t he upper port ion ( foreground) and a dense cover o f red alder i n the lower por t ion.
- 48 -
Because s l i d e development could not be fo l lowed i n th i s s tudy
over a p e r i o d o f t i m e f r o m i n i t i a t i o n , t h e l a g i n establishment of
trees could not be determined either i n absolute terms or i n r e l a t i o n
t o a par t icu lar s tock ing densi ty . However, a comparison o f mean
average ages o f sample t rees with s l i d e ages was considered useful i n
making a r e l a t i v e assessment o f r a p i d i t y o f c o l o n i z a t i o n among
species and slope posit ions. Considering a l l species and age
classes, the average difference between mean sample t r e e age and
s l i d e age was s ign i f i can t l y h ighe r i n the upper slope posit ion
(11 years) than i n the middle or lower posit ions (7 years). The
greatest d i f ference occurred with red a lder ; the mean o f 19 years
d i f fe rence fo r the upper s l ide was s ign i f icant ly h igher than the 7
and 9 years for the middle and lower s lope posi t ions, respect ively.
No s ign i f icant d i f ferences occurred among s lope pos i t ions i n age
dif ferences for western hemlock ( 9 , 7, and 5 years) or Sitka spruce
(10, 7, and 7 years) f o r upper, middle, and lower slide, respectively.
3.3.4 Tree composition by basal area
For a l l p l o t s ( v a r i a b l e or f ixed) containing t rees over 1.3 m i n
height, the composit ion of red alder based on basal area
(cross-sectional area o f t r e e stem a t 1.3 m he ight ) was s i g n i f i c a n t l y
greater on s l ides than i n logged or old-growth stands and greater i n logged than i n old-growth stands (Table 17). I n contrast, western
redcedar and yellow cypress made up a s ign i f i can t l y h ighe r p ropor t i on
o f old-growth stands than o f s l i d e s or logged areas (Table 17). The
p r o p o r t i o n o f t o t a l c o n i f e r s based on basal area decreased
s i g n i f i c a n t l y from old-growth t o logged t o s l i d e areas (Table 17). A
comparison o f percentage tree composition based on basal area made
between logged and s l i de p lo t s on l y up t o 55 years o f age ( the o ldes t
logged plots studied) gave r e s u l t s s i m i l a r t o t h o s e i n Table 17
except that the percentage composi t ion of Si tka spruce was no t
s i g n i f i c a n t l y g r e a t e r on s l ides than i n logged stands.
- 49 -
TABLE 17. Percentage composition by basal area for major tree species for s l ide , logged, and old-growth stands
State Speciesa
D r Hw ss cw cy AU con i fe r&
"""""" % """"""""
S l i d e C45 a 14 b 32 a 3 b l b 55 c
Logged 18 b 59 a 21 b 2 b O b 82 b
Old growth I C 48 a 12 b 28 a 10 a 99 a
a D r = Red alder; Hw = Western hemlock; Ss = S i t k a spruce; Cw = Western redcedar; Cy = Yellow cypress.
b Includes minor species.
C Within columns, means fol lowed by the same l e t t e r a r e n o t s i g n i f i c a n t l y d i f f e r e n t a t t h e 0.05 l e v e l (Student-Newman-Keuls' M u l t i p l e Range Test).
3.3.5 Vegetation groups
The COENOS and PFC vegetation analyses programs d i d not organize
t h e v e g e t a t i o n p l o t s i n t o s u f f i c i e n t l y homogeneous or d i s t inc t groups
t o a l l ow d i rec t co r re la t i ons o f p l a n t groups with age and hab i ta t
factors. The analyses, however, d i d a i d i n a more subject ive
grouping based on dominant p lan ts f o r each vegetat ion layer. Al though s l ides were sampled i n both the CWHg and CCPH
biogeocl imat ic zones, d i f ferences i n pa t te rns o f revegeta t ion between
these zones were no t su f f i c i en t l y ma jo r i n the survey sample areas t o
warrant their separation. Minor dif ferences are noted i n the group
descr ip t ions, inc lud ing d i f ferences between the CWHgl (submontane)
and CWHg2 (montane) var iants .
- 50 -
Eight groups were described for slides and three groups were described for logged areas. A few unique plots on slides are discussed separately. Common species (those occurring i n a t l e a s t 40% of the plots i n a group) are listed i n Table 18. In some plots, poor si te conditions, browsing by deer, and a lack of plant reproductive structures made separation o f some species impossible.
Approximately 35% of the plants occurred i n a t l e a s t 5 of the 11 groups and many plants were common f o r both slides and logged stands. I n addition, many of these species are also a conspicuous element of old-growth stands (Table 18) 1. Slide vegetation groups
Suggested relationships among the vegetation groups are i l l u s t r a t ed i n Figure 22. These relat ionships re la te primarily t o soil conditions and to stage o f development.
Group 1. T h i s group represents the ear l ies t s tage i n the revegetation o f landslides. The substrate is exposed bedrock or a mixture o f rubble and mineral so i l . Revegetation on bedrock proceeds slowly and is restr ic ted to pockets of mineral soil located i n crevices and shallow depressions, Mineral s o i l and rubble substrates are often unstable and plant colonization is retarded by continuous surficial erosion, especially on the upper slope position. Slides i n t h e CWHg2 (montane) variant tended to be steep i n the lower slope position also, and erosion of material from t h i s position into creeks and ravines was common.
Debris such as logs, fa l len t rees , and stumps occasionally line the edges o f slides or become stabi l ized on level benches or gentle slopes, Their presence permits plant colonization. Ridges between gullies generally become revegetated before gully bottoms. Plants also invade recent slides as clumps broken from eroding scarp faces come t o r e s t on gentler terrain or become trapped by debris.
Total vegetative cover of the group varies from l e s s than 1 to 11%, with the average cover higher i n CWHgl plots (3 .5%) than CWHg2 (1.0%). The la t te r p lo ts a l so had the lowest diversity of species.
- 51 -
X
X
x x x x x x
x x x x x x x x
x x x x x x x x x x
X
x x x
X
x x
X
X
X
X
x x x
X
X
x x
x x x
X
x x
X X
x x x x x
x x x x
x x x x x x x x
x x x x x x x
x x
x x x x x
x x x x x
x x
x x x x x
x x x x x x x
x x x x x x x
X
x x
X
x x
x x
X
x x x
x x x
x x
- 52 -
X
X X
x x x
x x x
X X
X X X
x x
x x
X x x x x x x x x x
x x x x
x x x x
x x
x x
X
X
x x
x x
x x x
x x x
x x x
x x
x x x x x x x
x x X x x
x x x x x x x x x
x x x x x x x x x x
x x x x x x x x x x
- 53 -
x x x x x x x x x
x x x x x x x x x x
x x x x x x x x x x x x
x x x x x
x x x x x x X
x x x x x x
x x x x x x
x x x x
x x x x x x x x x x
X x x x
x x x
X x x x x
x x x x x x x x x x x
x x x x
X
oc, a, m m m m m m m m m m m m m m m m 2
- 54 -
MAJOR PATHWAYS
- - - - - - - MINOR PATHWAYS
FIGURE 22. Relat ionships among the e igh t s l ide vegeta t ion groups and old growth. G = Group.
- 55 -
Western redcedar, western hemlock, Sitka spruce and yel low
cypress (CWHg2 and CCPH only) are occasional ly present as low shrubs or seedlings with a cover o f 1% or less. - Rubus s p e c t a b i l i s i s t h e
only commonly occurring shrub species (Table 18). Most cover comes
from herbs and bryophytes (14% each). Blechnum spicant and Luzula
p a r v i f l o r a a r e common herbs. - Carex mertensi i , Epi lobium spp.
(E. delicatum and - E. glandulosum), Athyrium fi l ix-femina ssp.
cyclosorum, Polystichum spp. (P. - munitum and - P. l o n c h i t i s ) , Senecio
sy lva t icus and - S . vulgar is) , and Tolmiea menziesii occur
occasionally.
Bryophytes include those typical ly found on exposed mineral
s o i l . Poqonatum contortum i s common and - P. alpinum and Polytrichum
commune are occasional ly present. I n addition, Rhytidiadelphus
loreus, S tokes ie l la oregana, and Dicranum fuscescens may be present
on organic debris.
Most o f t h e p l o t s i n t h i s group were s i t ua ted on s l i des l ess
than 10 years of age. However, especia l ly on steep, upper slopes, i t may be several decades before an appreciable cover of vegetation i s
obtained. For instance, one p l o t i n t h i s group on a 38-year-old
s l i d e had a to ta l vegeta t ive cover o f less than 1%.
Group 2. This group i s representat ive o f vegetat ion on a
smal l number o f p l o t s sampled i n both b iogeocl imat ic zones. I t i s character ized by a high cover of herbs and/or bryophytes on recent ly
fa i led s lopes with a r e l a t i v e l y deep, s tab le minera l so i l subst rate.
It may be present on a part of s l ides otherwise character ized by
Group 1 or by a greater cover of red a lder.
Total cover i s var iab le bu t exceeds 16%. Red alder, western
hemlock, S i t ka spruce, and western redcedar (of ten severely browsed)
are common tree species of the low shrub layer wi th a combined t o t a l
cover o f 5% or less. The shrubs Rubus spec tab i l i s and Vaccinium spp.
are common but a re l im i ted to a cover o f 1% or l ess by deer browsing.
- 56 -
Cover o f herbs and bryophytes i s general ly between 15 and 40%, each with intervening bare areas of bedrock and mixtures of rubble
and minera l so i l . Common herbs are Blechnum spicant, Polystichum
spp., Cirsium vulgare, Epilobium spp., Trisetum cernuun, Luzula
parv i f lora, Athyr ium f i l ix - femina ssp. cyclosorum, Tolmiea menziesii,
and Senecio spp. The cover o f bryophytes includes Pogonatum contortum,
Polytrichum commune, Rhytidiadelphus loreus, and Dicranum
fuscescens. P e l l i a spp. are often present on moist, seepy microsi tes.
Group 3. This group, t h e f i r s t o f t h r e e dominated by red
alder, i s characterized by an extensive cover o f r e d a l d e r in' the
t a l l or low shrub layers. It i s found t y p i c a l l y on middle and lower
slopes i n which t h e s u b s t r a t e o f s o i l and rubble i s s t a b l e and moist, and p a r t i c u l a r l y when associated with fine sedimentary, calcareous,
or sof t vo lcan ic bedrock. Representative vegetation of the group
occurs on s l ides vary ing i n age from 3 t o 33 years o f which the
major i ty are less than 10 years o f age.
The to ta l vegeta t ion cover i s between 60 and 100% (31% i n one
p l o t with a high rubble cover). In general, red alder dominates and
other p lant species are suppressed and of low cover. Western
hemlock, Sitka spruce, and western redcedar are present i n the low
shrub layer, of ten with a t o t a l combined cover o f l e s s t h a n 5%.
The shrubs Rubus spec tab i l i s and Vaccinium spp. are common but
are maintained at a cover o f l e s s t h a n 1% by severe browsing.
Herb cover varies between 1 and 20%. Plants are sparsely
scattered underneath the dense alder or i n patches i n small
openings. The most common species are Luzula parvi f lora, Blechnum
spicant, Agrostis scabra, Cirsium vulgare, Polystichum spp.,
Gymnocarpium dryopteris, Epi lobium spp., Galium t r i f lorum, Tr isetum
cernuum, and Athyr ium f i l ix - femina ssp. cyclosorum.
- 57 -
Bryophyte cover i s general ly 3% or less. Species include many
common t o Groups 1 and 2 and t o undisturbed forested areas, such as
Hylocomium splendens, Pogonatum alpinum, - P. contortum, S tokes ie l la
oregana, Rhyt id iadelphus loreus, Pel l ia spp., and Conocephalum
conicum.
Group 4. As a l a t e r s t a g e o f Group 3, t h i s group i s
represented by p lots on s l ides 14-45 years o f age. Total cover i s 80-100% and i s dominated by r e d a l d e r a t about 60% cover and 10 rn i n
height., The number o f stems per hectare i s much reduced from the
Group 3 stage. Sitka spruce usually dominates the understory t a l l
shrub layer and on a few of the o lder s l ides equals or nearly equals
the a lder i n height. Sitka spruce also occurs as a low shrub and i t s
t o t a l cover i n a l l l a y e r s may exceed 20%. Western hemlock i s a lso
common i n the shrub layer but i s usually shorter than the spruce.
Western redcedar stems a r e f a i r l y numerous but, as a r e s u l t o f
browsing, t o t a l c o v e r r a r e l y exceeds 1%. I n some areas o f
inexpl icably l ight browsing pressure, Rubus spectabi l is reaches more
than 10% cover as a t a l l shrub. Along with Vaccinium spp., i t i s
normally present only as a low shrub. Herb cover varies between less than 1 and 25%. The most common
species are Trisetum cernuum, Galium t r i f lorum, Athyr ium f i l ix - femina
ssp. cyclosorum, Polystichum spp., V io la spp., and Blechnum spicant. Species more cha rac te r i s t i c o f open exposure, such as Cirsium vulgare, Senecio spp., and Epilobium spp., occur much l ess f requent ly
or are absent i n t h i s group.
Bryophyte cover i s about 30% on most plots, considerably h igher
than i n Group 3 . Species are general ly character ist ic of non-sl ide,
fo res ted s i tes and include especial ly Rhyt id iadelphus loreus and
Stokes ie l la oregana. Other common species include Hypnum c i r c i n a l e ,
Dicranum fuscescens, Plagiothecium undulatum, Scapania bolanderi,
Rhizomnium glabrescens, Pogonatum alpinum, Rhacomitrium spp.
(R. - canescens and - R. heterostichum) , Isopterygium elegans,
Diplophyllum albicans, Plagiomnium insigne, Leucolepis menziesii, and
P e l l i a spp.
- 58 -
Group 5. This group represents a l a rge number o f p l o t s
sampled on s l ides aged 60-102 years, pr imari ly i n the CCPH zone and
CWHgl (submontane) var iant . The vegetation i s dominated by red a lder
i n the main canopy where i t has a cover of less than 50%. The decadent red a lde r i s being supplanted i n dominance by coni fers
released from the understory. Sitka spruce is common as a t a l l shrub
or s m a l l t r e e j u s t underneath the canopy o f r e d a l d e r . I t s c o v e r
ranges from 10 t o 40%. Western hemlock i s of ten present but i s usua l ly shor te r i n height and lower i n cover than the Si tka spruce.
Western redcedar and occasionally yellow cypress (CCPH and CWHg2) are
present as smal l t rees or t a l l shrubs with a cover o f 5-10%; these
poss ib ly became well established before deer browsing reached
c r i t i c a l l e v e l s . Severely browsed Rubus spec tab i l i s and Vacciniurn spp. are common
shrubs but only reach 1% cover and are seldom over 2 m i n height.
I n general, herb cover i s l e s s t h a n 5%. Common species include
Polystichum spp., Athyr ium f i l ix- femina ssp. cyclosorum, Blechnum
spicant, Carex mertensi i , and Luzula parv i f lora. Polypodium vulgare
ssp. occidentale i s sometimes present as an epiphyte on red alder.
Less common species include Tricetum cernuum, S t e l l a r i a c r i s p a , and
Dryopter is ass imi l is .
Bryophyte cover i s var iab le bu t genera l l y exceeds 60%. On some
p lo ts , spec ies a re con f ined to e leva ted pos i t ions o f f the fo res t
f l o o r on logs and the base of trees. The remain ing forest f loor is covered with l e a f l i t t e r . R h y t i d i a d e l p h u s l o r e u s has the h ighes t
cover, with Pogonatum alpinum and Stokes ie l la oregana a l so o f ten
occurr ing i n large patches. Other common species include Leucolepis
menziezii, Rhizomnium glabrescens, Plagiothecium undulatum, and
Scapania bolanderi. Conocephalum conicurn and P e l l i a spp. are usual ly
present on moist, seepy microsites.
Group 6 . This group i s represented by p l o t s i n the upper and
middle s lopes o f s l ides 14-48 years of age. I t i s characterized by a
low cover o f c o n i f e r s i n the low and occasional ly t a l l shrub layers.
- 59 -
The substrate o f largely coarse rubble and bare bedrock keeps t o t a l
plant cover low, i .e., less than 40% and confined t o pockets o f humus
and m i n e r a l s o i l i n s m a l l depressions and f i ssures i n the bedrock
surface. Red alder is not a component though i t may be present on
more s u i t a b l e s i t e s o f the same s l i de .
Western hemlock or Sitka spruce are the dominant species but are
usua l ly less than 2 m i n height. Lodgepole pine (Pinus contorta) i s occasionally present with a he igh t o f less than 10 m. Deer browsing
and poor s i t e cond i t i ons keep western redcedar and ye l low cypress t o
less than 1 m i n height and 5% i n cover. Sitka alder (Alnus sinuata)
i s occasionally present as a low shrub. Conifer seedlings are
usua l ly common.
The shrubs Rubus spec tab i l i s and Vaccinium spp. are common and
Gaulther ia shal lon and Menziesia ferruginea are occasional, but none
exceed 2% i n cover. Herb cover is general ly 5% or less. Agrostis scabra, Blechnum
spicant, Epilobium sp., Polystichum spp., V io la spp., and Trisetum
cernuum are the most common species. I n addition, lycopodium
clavatum was common on CWHg2 va r ian t p lo t s and Galium t r i f l o rum,
Lycopodium selago, Adiantum pedatum ssp. aleuticum, Carex mertensi i ,
and Prenanthes a la ta were common i n CCPH zone p lo ts .
Bryophyte cover on most p l o t s i s 10% or less. Common species on rock and exposed mineral s o i l are Poqonatum contortum, Diplophyllum albicans, Rhacomitrium spp., and Dicranum fuscescens.
Rhytidiadelphus loreus and Scapania bolander i are commonly found
underneath shrubs.
Group 7. Three landsl ides i n the CWHgl (submontane) var iant
developed a s t r i c t l y c o n i f e r t r e e cover with no or i n s i g n i f i c a n t
numbers o f red a lder stems on a l l slope posit ions. The s l ides var ied
i n age between 35 and 38 years.
Total vegetative cover usually exceeds 90%, mainly western
hemlock (50% cover) i n the t a l l or low shrub layers. Sitka spruce i s
less abundant, with a cover usually less than 20%. Western redcedar
- 60 -
is commonly present b u t does not exceed 1% cover or 2 m in height because of browsing pressure. Lodgepole pine is an unusual component of some plots in the shrub or tree layers.
Common shrubs are Gaultheria shallon and Vaccinium spp. They are confined to the low shrub layer and a t o t a l cover of less than 5%.
Herb cover does not exceed 2%. Blechnum spicant and Lycopodium clavatum are the only c o m n species. - L. selago, Epilobium spp., Listera cordata, and Trisetum cernuum occur occasionally.
Bryophyte cover varies between 2 and 45%. Common species are Rhytidiadelphus loreus, Scapania bolanderi, Pogonatum contortum, Rhizomnium qlabrescens, and Stokesiella oregana. Occasional species include Plagiomnium insigne, Hylocomium splendens, Dicranum fuscescens, and Plagiothecium undulatum.
Group 8. T h i s group is represented by p lo ts on slides 48-155 years of age. I t d i f f e r s from Group 7 by a dominant cover (30-60%)
o f Sitka spruce and less (5-413%) of shorter western hemlock. Western redcedar and yellow cypress are occasionally present beneath the main canopy of Sitka spruce. Red alder is occasionally present and may i n some cases have been present in greater abundance i n earlier stages. In some stands, however, there is no indication of red alder ever being present.
Shrub species are low in cover. Vaccinium spp. a re common and Rubus spectabi l is is occasionally present.
Herb cover i s 1% or less. Blechnum spicant, Dryopteris assimilis, and Luzula parvif lora are common species.
bryophyte cover is also 1% or less b u t often consists o f a large number of species. Those which are common include Dicranum fuscescens, Hookeria lucens, Hypnum circinale , Hylocomium splendens, Isopterygium elegans, Leucolepis meriziesii, Mnium glabrescens, Pell ia spp . , Plagiothecium undulatum, Pogonatum alpinum, Scapania bolanderi, and Stokesiella oregana.
- 61 -
2. Unique slides P l o t s i n a number of slides were d i f f i c u l t t o f i t i n to any of
the foregoing groups. They are briefly described i n the following sect ion.
Kaisun 1 and 4. Vegetation on two of the three slides sampled on the exposed, salt-spray influenced west coast of Moresby Island appeared t o be similar t o the Spruce-Reedgrass ecosystem uni t described by Banner " e t a l . (1986) and Lewis (1982). Vegetation was dominated by a canopy of Sitka spruce and an understory of Calamagrostis nutkaensis.
Peel 1. The substrate on t h i s slide was a mixture of bare bedrock, rubble, and shallow mineral soil. Total vegetation cover by plot varied from 24 to 48%. Trees and shrub species were similar t o those common on other slides. Herb cover was h igh and consisted of several species rarely or never present on other slides, e.g., Adiantum pedatum ssp. aleuticwn, Campanula alaskana, Carex anthoxanthea, "- C. aurea, C. scirpoidea, and Parnassia fimbriata. High
s o i l pH levels (6.4 versus an average of 5.3 for other similarly aged slides) and ample soil moisture probably contributed to the uniqueness in p l an t composition.
Phantom 1. This was a 36-year-old s l ide located t ransi t ional ly between the montane variant of the CWg subzone and the MH (Mountain Hemlock) zone. Both western hemlock and mountain hemlock (Tsuqa mertensiana) were present in the t a l l and low shrub layers. Sitka spruce and yellow cypress occurred wi th less cover. On the upper portion of the sl ide, Calamaqrostis nutkaensis formed a dense cover. In the middle and lower portions, herb cover was less dense and consisted of Athyrium filix-femina ssp. cyclosorum, Blechnum spicant, Carex anthoxanthea, - C. macrochaeta, Coptis asplenifolia, Cornus unalaschkensis, Epilobium spp., Gymnocarpium dryopteris, Lycopodium selago, Luzula parviflora, Tiarella t r i f o l i a t a , Viola spp . , and Veratrum eschscholtzii.
- 62 -
Rennell 9 . This 8-year-old sl ide was characterized by a very low
frequency o f t ree spec ies and numerous herb species dominated by large
patches o f t h e sedge Carex laeviculmis.
South Bay 5. This 14-year-old s l i d e was seeded i n 1980 with
severa l agronomic grasses and legumes. The herb layer was dominated by
severa l o f these inc lud ing Agros t is - alba, Dactyl is glomerata,
Oeschampsia elongata, Festuca rubra, and Lol ium perenne.
Sue Lake 1. The middle and lower por t ions o f th is 11-year-o ld
s l i d e were dominated by the herb Equisetum telmateia, not a usual
component o f s l i d e vegetation. Cover for this species ranged from 70%
on the l ower po r t i on t o 23% i n the middle corresponding to decreasing
so i l mo is tu re f rom the bo t tom to the top o f the s l ide . The abundance o f
- E. te lmate ia was probably re la ted to very mois t so i ls as evidenced by some pools o f standing water located in shallow depressions, p a r t i c u l a r l y on the lower s lope o f the s l ide.
3 ) Logged vegetat ion groups
Three groups (9-11) characterize the vegetation of logged stands.
Group 9 represents logged stands between 1 and 7 years o f age. Group 10
i s t y p i c a l o f o l d e r stands up t o 25 years o f age and dominated by
con i fe rs , the most usual s i tuat ion for logged s tands. I n contrast,
Group 11 describes logged stands with a s i g n i f i c a n t component o f r e d
alder. Logged stands over 25 years o f age were so heterogeneous t h a t
they were not assigned to vegetat ion groups. However, common species
from these plots are documented i n Table 18.
Group 9 . Total vegetative cover i n these young, logged stands i s
h igh ly var iab le and appears t o b e r e l a t e d t o t h e degree o f s o i l
disturbance and amount o f s l a s h l e f t from logging operations. High to ta l vegetat ive cover i s usua l ly a r e s u l t o f h i g h r e s i d u a l b r y o p h y t e
cover.
- 63 -
Western hemlock i s the dominant con i fe r i n the low shrub layer with
a cover usually exceeding 10%. Sitka spruce i s a lso common b u t i t s
cover rare ly exceeds 5%. Western redcedar and yellow cypress are
occasional ly present but ne i the r exceeds a cover o f 1% or a height o f 1
m because o f browsing by deer. Red a lder i s also occasional ly present
bu t i t usua l ly has a cover o f l e s s t h a n 1%. Total shrub cover rarely exceeds 5%. Menziesia ferruginea, Rubus
spec tab i l i s , Sambucus racemosa ssp. pubens, and Vaccinium spp. are common.
Herb cover i s usua l ly less than 5%. Athyr ium f i l ix- femina ssp.
cyclosorun, Blechnum spicant, Copt is aspleni fo l ia, Maianthemum
di latatum, and Senecio spp. are common.
Common bryophytes are Dicranum fuscescens, Hylocomium splendens , Plagiothecium undulatum, Polytrichum commune, Rhytidiadelphus loreus,
Scapania bolanderi, and Stokes ie l la oregana.
Group 10. This conifer-dominated, older logged vegetation group
has a t o t a l p l a n t cover of up t o 60%. Western hemlock dominates with a
cover o f 30-60%. Sitka spruce i s a lso common but has a cover less than
20%. Western redcedar and yellow cypress (CCPH and CWHg2) are o f ten
present but because o f browsing they are restr icted to the low shrub
l aye r and a cover o f 1% or less.
Total shrub cover i s genera l ly less than 10%. I n a d d i t i o n t o Rubus spec tab i l i s and Vaccinium spp., Menziesia ferruginea is a common shrub
species but i t a lso ra re l y exceeds a height o f 1 m because o f browsing
by deer.
I n general, the cover of herbs i s 10% o r less. They o f ten occupy
exposed areas along the margins of conifer clumps and p i l e s o f s l a s h .
Common species inc lude Athyr ium f i l ix - femina ssp. cyclosorum, Blechnum
spicant , Copt is asplen i fo l ia , Luzula parv i f lora, Maianthemum di latatum,
Polystichum spp., and Trisetum cernuum.
Bryophyte cover i s usua l ly less than 50%. Common species are
Dicranum fuscescens, Hylocomium splendens, Hypnum c i r c ina le , Rhizomnium
glabrescens, Plagiothecium undulatum, Polytrichum commune,
Rhytidiadelphus loreus, Scapania bolanderi, and Stokes ie l la oregana.
- 64 -
Group 11. Red a lder i s the dominant species o f t h i s group,
present e i ther i n t h e t a l l shrub or main t r e e canopy layer. I t s
cover varies between 35 and 85%. As i n young, red alder-dominant,
s l i d e p l o t s , r e d a l d e r suppresses other p lant species. Si tka spruce
i s o f ten t he dominant understory conifer but obtains a cover o f l e s s
than 5%. Western hemlock i s even l e s s abundant than S i tka spruce.
I n general, shrubs have a cover of less than 5%. Those commonly
included are Rubus spec tab i l i s and Vaccinium spp. Menziesia
ferruginea and Sambucus racemosa ssp. pubens are occasional
components. Herb cover i s usua l ly between 5 and 20%. Common species include
Athyr ium f i l ix - femina ssp. cyclosorum, Blechrwm spicant, Coptis
asp len i fo l ia , Dryopter is ass imi l i s , Galium t r i f lo rum, Luzu la parvi f lora, Polyst ichum spp., Prenanthes a la ta, and Trisetum cernuum.
Bryophyte cover i s usua l ly between 20 and 40%. Rhytidiadelphus
lo reus usua l ly dominates. Other common species are Conocephalum
conicum, Dicranum fuscescens, Isopterygium elegans, P e l l i a spp., Plagiomnium insigne, Plagiothecium undulatum, and Rhizomnium
glabrescens.
3.4 Forest Growth and S i t e P r o d u c t i v i t y
3.4.1 Ear ly he igh t g rowth ra tes o f t rees
The r e s u l t s o f stem analyses o f young red alder, Sitka spruce,
and western hemlock on s l i d e s and i n surrounding logged areas are
shown in Figure 23. Linear regressions were s i g n i f i c a n t l y d i f f e r e n t
between s l i d e and logged areas for a l l species. For western hemlock
and Sitka spruce, height growth i n logged stands was about double the
r a t e o f t h a t on s l i d e s f o r t h e same species. Red alder height growth
was about tw ice tha t o f con i fe rs on logged areas and 5 t o 6 times
t h a t o f the con i fe rs on s l ides (F ig . 23). Height growth o f r e d a l d e r
was greater i n logged stands than on s l ides bu t d i f fe rences were much
l e s s marked than for the coni fers . Ear ly he ight growth on s l i des was
s i g n i f i c a n t l y l e s s i n the upper s lope posi t ion for both Si tka spruce
and western hemlock.
- 65 - - - RED ALDER - SITKA SPRUCE """ WESTERN HEMLOCK
1000 1 ; i
5 IO IS 2 0
Age (years)
FIGURE 23. Early height growth of red alder, western hemlock, and S i t ka spruce i n s l i d e (S) and logged (L) areas. R2 f o r a l l regressions >O. 99.
3.4.2 Basal area production
As one assessment o f p roduc t iv i t y , the basa l a rea o f s tands on
s l i d e and logged plots up t o 55 years o f age were compared.
S ign i f i can t ly h igher average western hemlock and to ta l con i fe r basa l
areas occurred i n the logged than i n the s l ide s ta te (Tab le 19) . The
t o t a l ( c o n i f e r plus deciduous) basal area averaged more i n logged
stands than on s l i d e s but the d i f fe rence was no t s ign i f i can t
(Table 19) . Compared on an age class basis, t he basal area of conifers and
of coni fers p lus deciduous t rees on logged areas was markedly higher
than on s i m i l a r l y aged s l i d e s , s i g n i f i c a n t l y so fo r t he 30- t o
59-year age class (Table 20). The to ta l basa l a rea o f con i fe rs i n
the 30- t o 59-year c lass (avg. = 41 years) o f logged stands was even
s ign i f i can t ly h igher than tha t i n the group o f s l ides over 60 years
o f age (avg. = 85 years) (Table 20). The reverse was t rue f o r red
alder basal area. No s ign i f i can t d i f fe rence occur red i n t o t a l b a s a l
area. Old-growth stands had s i g n i f i c a n t l y h i g h e r average basal areas
f o r c o n i f e r s t h a n a l l o t h e r age class/state combinations. They a lso
had s ign i f icant ly h igher basal area for a l l species than a l l other
age class/state combinations excepting the 30- t o 59 year
- 66 -
TABLE 19. Mean basal area for major t ree species for s l ide and logged stands up t o 55 years o f age
State Speciesa
D r Hw ss CW CY Tota l b Grandb c o n i f e r t o t a l
"""""" $/ha - - - - - - - - - _ - _ Sl ide C3.5 a 0.7 b 2.7 a 0.0 a 0.0 a 3.6 b 7.2 a
Logged 3.5 a 4.4 a 3.8 a 0.8 a 0.0 a 9.0 a 12.5 a
a D r = Red alder; Hw= Western hemlock; Ss = Sitka spruce; Cw= Western redcedar; Cy = Yellow cypress.
Includes minor species.
Means within columns fol lowed by the same l e t t e r a r e n o t s i g n i f i c a n t l y d i f f e r e n t a t t h e 0.05 l e v e l (Student-Newman-Keuls' M u l t i p l e Range Test).
- 67 -
TABLE 20. Basal area o f l i v e t r e e s for sl ide, logged, and old-growth stands by age c lass
Age Basal area
class State Coni fer Deciduous Tota l
1-14 S l ide a0.O e 1.6 b 1.6 d Logged 0.9 e 2.0 b 3.7 d
15-29 Sl ide 0.2 e 9.6 b 9.8 cd Logged 12.7 de 2.2 b 14.9 cd
30-59 S l ide 16.4 d 5.9 b 22.3 c Logged 49.6 b 11.1 b 60.7 ab
60+ Sl ide 33.7 c 19.7 a 53.4 b
150+ Old growth 63.9 a 0.5 b 64.4 a
a Within columns, means fol lowed by the same l e t t e r a r e n o t s i g n i f i c a n t l y d i f f e r e n t a t t h e 0.05 l e v e l (Student-hewman-Keuls' M u l t i p l e Range Test).
- 60 -
logged plots (Table 20). I n old-growth stands, considerable
addit ional basal area (22 m /ha) occurred i n dead, standing trees.
The grea tes t con t r ibu tor to th is ca tegory was western hemlock
(Table 21). Few dead t rees were recorded for sl ides (mainly red
a lder) and logged stands.
2
3.4.3 Wood volume product ion
A considerably lower volume o f t o t a l b o l e wood occurred on
s l ides than on logged areas with equivalent age classes (Table 22).
Because o f low p l o t numbers i n some groups and great var ia t ion,
d i f ferences were on ly s ign i f i can t fo r the o ldes t logged age class,
i .e., 30-59 years (Table 22). Coni fer volumes were pa r t i cu la r l y l ow
on s l ides less than 60 years o f age. The volume r a t i o o f Sitka spruce t o western hemlock for the 30-
t o 59-year age c lass was higher i n slides (10.9:l) than i n logged
areas (1.1: 1) or o l d growth (0.2: 1). D e s p i t e t h i s h i g h e r r a t i o on
s l ides , the average t o t a l volume o f S i t k a spruce remained less than
i n equivalent logged sites.
The percentage reduction of the commercial ly important conifer
volumes on s l ides versus logged s i tes was 93, 99, and 72 f o r 1- t o
14-, 15- t o 29-, and 30- t o 59-year age classes, respectively
(Table 22). I n the 30- t o 59-year c lass , fo r example, the greatest
reduct ion occurred at the top of the s l ide (94%), less a t the lower
slope (76%), and leas t a t the midd le (38%). I n comparison with o l d (>60 y r ) s l i d e s (avg. = 85 y r ) ,
old-growth stands had s i g n i f i c a n t l y l a r g e r volumes o f western
hemlock, western redcedar, and yellow cedar and smaller volumes o f
red a lder and Sitka spruce (Table 23). Even the o ldes t s l ides
(>80 yr) averaging 107 years had propor t ional ly low covers o f
hemlock, western redcedar, and yellow cypress and h igh covers o f
Sitka spruce and red a lder compared with old-growth stands (Fig. 24).
- 69 -
.
TABLE .21. Mean basal area o f dead, s tand ing t rees fo r a l l s l ide , logged, and old-growth p lots
State Soeciesa
D r Hw ss cw CY To ta l con i ferb
- _ - - - - - - - - - $/ha - - - - - _ - - - - " _ _ S l i d e C1.2 a 0.2 b 0.3 a 0.1 b 0.1 b 0.7 b
Logged 0.1 a 0.1 b 0.1 a 0.1 b 0.0 b 0.3 b
Old growth 0.1 a 14.1 a 0.9 a 2.9 a 1.5 a 22.1 a
a Dr = Red alder; Hw = Western hemlock; Ss = Sitka spruce; Cw = Western redcedar; Cy = Yellow cypress.
b Inc ludes t rees no t i den t i f i ed a t t he spec ies level.
Within columns, means fol lowed by the same l e t t e r a r e n o t s i g n i f i c a n t l y d i f f e r e n t a t t h e 0.05 l e v e l (Student-Newman-Keuls' M u l t i p l e Range Test).
- 70 -
TABLE 22. Volumes of l i v e t r e e s f o r s l i d e , logged, and old-growth stands by age c lass
Age class
State Volume Conifer Deciduous To ta l
1-14 S l i de a0.1 c 4.2 b Logged 1.4 c 8.8 b
15-29 S l i de 0.5 c 41.7 b Logged 43.0 c 11.0 b
30-59 S l i de 100.0 c 43.1 b Logged 353.5 b 123.7 a
60+ S l i d e 325.2 b 173.2 a
150+ Old growth 669.8 a 4.6 b
" " _ 4.3 c
10.2 bc
42.2 bc 54.0 bc
143.1 b 477.2 a
498.4 a
674.4 a
a Within columns, means fol lowed by the same l e t t e r a r e n o t s i g n i f i c a n t l y d i f f e r e n t a t t h e 0.05 l e v e l (Student-Newman-Keuls' M u l t i p l e Range Test).
- 71 -
TABLE .23. Comparison o f volumes o f t r e e s i n o l d s l i d e s 0 6 0 y r ) with those i n old-growth stands (>150 y r )
State Speciesa
D r Hw ss cw CY To ta l Grand c o n i f e r t o t a l
S l i d e b173 a 43 b 262 a 14 b 7 b 325 b 498 b 060 years)
Old growth 5 b 352 a 86 b 149 a 83 a 670 a 674 a
a Dr = Red alder; Hw = Western hemlock; Ss = Sitka spruce; Cw = Western redcedar; Cy = Yellow cypress.
Within columns, means fol lowed by the same l e t t e r a r e n o t s i g n i f i c a n t l y d i f f e r e n t a t t h e 0.05 l e v e l (Student-Newman-Keuls' M u l t i p l e Range Test).
- 72 -
30
m 20
IO
A
40
30
20
10
40 IB 30
rn
EO
10
C
! T I I .p ALDER
0
SITKA SPRUCE
YELLOW CYPRESS
b
\ \ \\
_r L
I A
WESTERN HEMLOCK
4 WESTERN REDCEDAR
Y Y LODGEPOLE
FIGURE 24. Average composition and s t ruc tu re o f stands: A. Upper slope, s l i des >80 years of age; B. Upper slope, old-growth; C. Lower s lope, s l ides >80 years o f age; D. Lower slope, old-growth.
- 73 -
4 DISCUSSION
Discussion of differences i n landslide characterist ics based on slope posit ion ( i .e. , upper, middle, and lower) refers t o debris avalanches i n the sense of Swanston and Swanson (19761, which include debris slides, debris flows, and the commonly encountered combinations o f these two types (Howes 1981). Debris torrents are not included because they lack a progression from scour a t t he top to deposit at t h e bottom. However, t he three debr i s torrents s tud ied are included i n t o t a l slide summaries of vegetation development and forest product iv i ty .
The average s ize of landslide studied (2.3 ha) exceeded that for other surveys, e.g., 0.21 ha (Chatwin and Rollerson 1984) and 0.3 ha (Schwab 1983).
The larger s ize i n t h i s s t u d y r e f l ec t s its more selective nature and concentration on landslides w i t h well-defined impacts on the s i te . I n addition, large landslides account f o r most of the total area affected. I n a survey of a section of the Queen Charlotte Islands, Rollerson (1984) found that landslides over 1.0 ha i n area accounted for on ly 12% of the number of s l i des b u t 67% of t h e area. I n the Rennell Sound area, Schwab (1986) found tha t slides greater than 0.5 ha i n s ize involved o n l y 25% of the fa i lures b u t
disturbed 67% of the land area. A large size also tends t o minimize complicating edge effects such as shading and sloughing of headwall and la te ra l scarps noted i n other studies (Endo and Tsuruta 1966; Hull and Scott 1982; Hupp 1983; Miles " e t a l . 1984; Shimokawa 1984).
The heterogeneity of s o i l materials, particularly arrangement and depth, prevented a pract ical s t ra t i f icat ion into natural zones, e .g . , s l ipface and debris fan (Mark " e t a l . 19641, scour and fill (Adams 19841, o r more complex systems (Langenheim 1956). The decision t o systematically zone t h e s l ides i n t o three t h i r d s of equal length was a compromise that made mapping a heterogeneous surface unnecessary, b u t it still provided information specific t o slope position. The d i v i s i o n s parallel Taylor 's (1932) c lass i f icat ion of landslides i n southeastern Alaska i n t o steep, d r y , upper slope, middle slope, and gentle, moist, lower slope. On average, t h e t o p two-thirds of s l ides were par t ia l ly scoured t o bedrock or more rarely t o a compact glacial till. The
- 74 -
middle th i rd conta ined some deposits, the amount and d i s t r i b u t i o n o f t h e s e
depending upon t h e o r i g i n a l topography and the distance from the edge of t he
s l i de . The lower th i rd consis ted main ly o f deposi ted so i l and organic
debris. Where debris avalanches were transformed t o flows a t t h e i r l o w e r end,
ma te r ia l was o f ten t ranspor ted comple te ly o f f the lands l ide s i te and i n t o
stream channels, thus account ing fo r the re la t i ve ly sha l low s o i l even i n the
l o w e r p a r t s o f t h e s l i d e s . P o s t - f a i l u r e e r o s i o n a l r i l l s and g u l l i e s were
present on many o f t he s l i de su r faces .
I n comparison with surrounding terrain, s l ides exhibi ted exaggerated
d i f fe rences i n phys i ca l cha rac te r i s t i cs from top t o bottom o f the s lope.
Spec i f i ca l l y , so i l dep th inc reased and bedrock exposure decreased. These
features were n o t s i g n i f i c a n t l y d i f f e r e n t from top t o bo t tom o f t he s lopes
adjacent to the sl ides. While the surrounds were no t deemed essen t ia l l y d i f f e r e n t from the pre-sl ide s i t es , an assumption v i t a l t o l a t e r comparisons
done i n the study, average slope gradient on the upper two- th i rds o f the
s l i d e s was s ign i f i can t ly h igher than on the adjacent surround. Thus, the
p r e - s l i d e s i t e was, on average, steeper or t h e f a i l u r e caused an increase i n steepness.
The development o f vegeta t ion on s l ide sur faces and the impact o f the
s l i d i n g on fo res t p roduc t i v i t y was r e l a t e d t o t h e n a t u r e o f p o s t - f a i l u r e s o i l materials. The average m id -s l i de so i l was a g rave l l y sandy loam h igh i n
coarse fragments as s imi la r ly repor ted fo r lands l ides i n Alaska (Adams and
S id le 1984). Compared with the adjacent surround, the upper layers o f s o i l s
on s l i d e s were h igh i n coarse fragments and low i n c lay and s i l t . T h i s
feature probably resulted from a tumbl ing act ion dur ing s l id ing and a mixing
o f n a t u r a l l y f i n e r and more completely weathered surface materials with lower
horizons, or a removal o f upper s o i l h o r i z o n s and exposure o f r e l a t i v e l y
coarse subsoi l . Addi t ional ly , for a number o f years a f te r fa i lu re s l ides a re
par t i cu la r ly sens i t i ve to sur face e ros ion by water (Cam 1983; Rollerson 1984)
and s l o u g h i n g o f s o i l , l i t t e r , and woody debr is from s l i d e margins. Surface
e ros ion t ranspor t s f i ne pa r t i c l es o f f t he s l i de l eav ing an armour o f coarse
fragments on the surface. The over-turning and m i x i n g o f s o i l d u r i n g s l i d i n g
also causes a r e d i s t r i b u t i o n o f surface organic mater ia l throughout the soi l
p r o f i l e and bur ies t ree bo les and other organic debr is produced by the slide.
- 75 -
A r e s u l t o f t h i s a c t i o n i s t h a t , except f o r an i n i t i a l l a c k of a surface
organic horizon, soi ls at the mid-slope of s l i des had average organic carbon
leve ls s im i l a r t o t hose i n the surrounding soi ls, i .e., 8% i n the upper and 4%
i n the l ower m ine ra l so i l p ro f i l e . S l i de so i l s were, on average, less acid,
warmer i n the summer, and had a lower C:N r a t i o t h a n s o i l s i n the surround.
Given comparable moisture conditions, they have a h igher potent ia l for
b io log ica l ac t i v i t y than those i n the surround. However, with establishment
o f vegeta t ion on the s l i des and with an apparent increase i n a c i d i t y o f
surface organic ,horizons with t ime, d is t inct ions between s l i d e and surround
should diminish with increas ing s l ide age.
The major i t y o f undis turbed so i ls i n th is s tudy were c l a s s i f i e d as
Ferro-Humic or Humo-Ferric Podzols as s imi la r ly repor ted fo r the Queen
Char lo t te Is lands by Townshend and Bourgeois (1978) and Lewis (1982). A f t e r
s l id ing, podzol features such as h i g h i r o n and aluminum content were
su f f i c ien t ly p reserved tha t even some recen t s l i de so i l s were c l a s s i f i e d as
podzols, a lbei t perturbated ones. Some s o i l s were simply truncated pre-sl ide
p r o f i l e s or overlays on top o f p re -s l i de so i l s . The percentage o f s o i l s
c l a s s i f i e d as podzols increased sharply with increasing age o f s l i des so t h a t
t he genera l c l ass i f i ca t i on (bu t no t p ro f i l e de ta i l ) o f so i l s on sl ides over 80
years o f age was s im i la r t o t hose i n old-growth stands and logged areas. Such
rapid "podzol izat ion" contrasts with the slow development on recent ly exposed
moraines (Crocker and Dickson 1957; Sondheim and Standish 1983). This study
concluded that most s o i l mater ia l remaining af ter shal low, debris avalanches
i s considerably a l tered from the parent mater ia l s ta te i n terms o f b i o l o g i c a l ,
chemical, and physical propert ies. Though severely d isturbed, the soi l has
not been destroyed and development o f p l a n t cover can proceed without a
primary phase. Exceptions t o t h i s l i e i n the more l i m i t e d areas scoured t o
bedrock or unweathered g l a c i a l till.
Although su r f i c i a l depos i t s usua l l y cons i s t o f ma te r ia l s from a mixture o f
rock types (Al ley and Thomson 19781, there were some apparent relat ionships
between the rock- type c lass i f i ca t ion and ce r ta in so i l p rope r t i es . Soils associated with g ran i t i c rock were relat ively coarse-textured. The coarse
conglomerates (Honna formation) were associated wi th s t rongly ac id so i ls with
- / 6 -
h i g h C:h ratios. Calcareous rock types were associated w i t h re la t ively high clay contents, low organic carbon contents and low C:FJ ra t ios . Hard volcanic rocks were associated with s o i l s high i n silt content and with re la t ively high pH and organic carbon levels. Soils associated wi th f ine sedimentary rocks were h i g h i n clay, silt, and organic carbon content.
Principal factors governing the rate and pattern of recovery on slides from a bare surface were soi l propert ies re la ted to associated rock types and slope position. The cover of surface organic matter increased exponentially with age of slide a t a s ignif icant ly fas ter ra te i n the lower t h i r d than i n the middle or upper t h i r d . The slowest increase i n humus cover was associated with the acid, coarse conglomerate rock type. The f a s t e s t occurred w i t h the fine sedimentary rock type and the mixture of types. Although attainment of an organic surface cover was often quite rapid, accumulation to any appreciable depth was extremely slow, presumably because o f a h igh biological ac t iv i ty on s l ides . Even on t h e oldest slides sampled, humus depths were l e s s than half those found i n logged and old-growth stands. I n contrast, Flaccus (1954) observed that organic matter i n the surface 10 cm of slides i n New Hampshire reached levels i n the surrounding forest w i t h i n 72 years. Relatively h i g h biological activity on the sl ides studied was also evidenced by the frequent occurrence of a mixed mineral and organic layer (Ah). This
condition was, i n par t , induced by mechanical mixing b u t a lso by t h e action o f
s o i l animals. Under a predominant cover of red alder, biological activity was o f t en suff ic ient ly h i g h tha t only a l i t t e r l ayer ex is ted on the s l ide surface. For a long period, therefore, slide surfaces remain sens i t ive to mechanical disturbance. That is, the i r mineral s o i l component is not protected by a thick organic mat as it is i n logged and old-growth stands. An increase i n organic carbon and decrease i n pH i n humus w i t h increasing sl ide age s ignals a s h i f t toward the lower biological activity o f old-growth, surface soi l . A more rapid increase i n humus depth, as observed by other authors for recently exposed moraines (Crocker and Major 1955; Crocker and Dickson 1957; Ugolini 1968), is expected to eventually occur.
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The humus o f logged and old-growth stands was composed o f a greater
p r o p o r t i o n o f r o t t e n wood than that on slides. Recently logged areas had
par t i cu la r ly h igh percentages o f ro t ten wood, probably resul t ing f rom
addi t ions o f decayed mater ia l from f e l l e d snags and the scat ter ing o f ro t ten , natura l logs dur ing logging operat ions (Smith and Wass 1983). Establishment
and growth o f western hemlock would be par t i cu la r ly favored by the abundance o f r o t t e n wood i n logged areas and t h a t o f S i t k a spruce by the exposed mineral
s o i l and m u l l - l i k e humus on s l ides (Kra j ina 1969).
The sha l low.so i l s , bedrock exposure, and s u s c e p t i b i l i t y t o e r o s i o n on the
steep, upper, and midd le th i rds o f s l ides resu l ted i n a slow increase i n t o t a l
vegetat ive cover re lat ive to the lower s lope. Since no s i g n i f i c a n t
d i f ferences i n cover occurred among slope posi t ions on immediately adjacent
logged or old-growth areas, the differences on s l i des resu l ted from the
s l i d i n g i t s e l f . E s p e c i a l l y sparse vegetation occurred on upper slopes o f s l ides associated with coarse conglomerate, g r a n i t i c , and hard volcanic rock
types. These types were also characterized by minimal establishment o f red
alder. In contrast , par t icu lar ly rap id revegetat ion, especia l ly o f red a lder,
occurred on lower slopes i n associat ion with calcareous and fine sedimentary
rock types and mixtures. Sitka spruce seemed t o have some o f t h e same
substrate preferences as red alder and, as observed by Taylor (1934), contrasts sharply with western hemlock i n th is respect . The occurrence o f red
a lder on logged areas was l o c a l and reached s i g n i f i c a n t numbers only i n associat ion with f i n e sedimentary rock types.
I n general, forest composition was re la ted most c l e a r l y t o associated rock
type on s l i d e s and l e s s c l e a r l y i n logged areas, and there was l i t t l e
c o r r e l a t i o n i n old growth. These f ind ings suggest t h a t as surface organic
mater ia l accumulates causing changes i n the surface mineral s o i l and as red
alder decl ines i n importance, the upper s o i l p r o f i l e and the composition o f
the fo res t become less and less in f luenced by the nature o f the parent
mater ia l . However, p roduc t i v i t y o f old-growth stands i n the Queen Char lo t te
Is lands has been cor re la ted with bedrock types (Warren and Matheson 1949;
Lewis 1982).
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Total vegetative cover on logged areas exceeded t h a t on s l i d e s when
s i m i l a r ages were compared because o f res idua l vegeta t ion le f t a f te r logg ing ,
anu the presence on logged areas o f r e l a t i v e l y deep, s tab le so i l s . By 100
years, average vegetative cover fo r bo th s ta tes exceeded the average for old-growth stands. This resul t impl ies that vegetat ive cover on s l i d e s and logged areas will eventual ly decrease as a r e s u l t o f n a t u r a l m o r t a l i t y and
windthrow.
I n con t ras t t o ea r l y repo r t s o f a dense and vigorous shrub and herb cover
on the Queen Char lo t te Is lands (Hopkinson 19311, these components were no t
dominant i n any of the three s ta tes-- logged, s l ide, o r o l d growth. As
described for old-growth stands by Pojar and Banner (1984) , both the v igor and
cover o f herbs and shrubs appeared severely reduced by the browsing o f deer
in t roduced dur ing the f i r s t quar te r o f the 20 th cen tury (Cowan 1956). Bryophytes, however, developed unmolested and increased i n cover steadi ly
a f t e r s l o p e f a i l u r e and l o g g i n g t o a level considerably h igher than i n old-growth stands. Alaback (1982) showed bryophyte biomass increasing sharply
a f t e r l o g g i n g o f spruce-western hemlock forests t o about 125 years, then
decreasing t o about 60% o f t h a t l e v e l i n stands over 300 years. This study
p red ic t s a s i m i l a r decrease i n bryophyte cover on sl ides older than the ones
s tud ied, as natura l mor ta l i ty causes increased stand opening.
On average, s tock ing o f t rees on s l i d e s and i n logged areas reached levels
sa t is fy ing re fo res ta t ion s tandards . However, d i s t r i b u t i o n was o f ten clumped
and dependent on su i tab le, s tab le subst rates, par t icu lar ly i n the upper
por t ions of slides. Patchiness i n logged stands was more o f ten t he resu l t of concentrations o f s lash prevent ing t ree establ ishment and growth. Based on
number of stems, western hemlock was most numerous p a r t i c u l a r l y on the upper
s lope pos i t i ons o f s l i des , a s imi la r resu l t to tha t repor ted by Tay lo r (1932)
for l ands l ides i n Alaska. Western hemlock was a lso more numerous i n the upper
slopes o f logged stands than the lower. High numbers of western hemlock were
associated with gran i t i c rock types and h igh numbers o f red a lder with
calcareous rock types. When percentage composition was expressed by e i t h e r
number o f stems or basal area, western hemlock emerged as the dominant t r e e
species i n logged and old-growth stands. The dominant trees by basal area for
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s l i d e s were red a lder and S i t ka spruce. Although western redcedar and yel low
cypress were present i n s ign i f i can t amounts i n old-growth stands, their
cont r ibut ion to logged s tands was small. This may r e f l e c t j u s t slow growth
ra tes or may indicate increasing impacts of deer i n the past 50 years. As
observed f o r old-growth stands (Pojar and Banner 1984), western redcedar and
yel low cypress are ut i l ized by deer on s l ides and logged areas a t a
s ign i f i can t ly h igher leve l than S i tka spruce and western hemlock. There a re seve ra l reasons f o r t he d i f f i cu l t y i n descr ib ing homogeneous
vegetat ion groups that ref lect a d isc re te se t o f s i te cond i t ions . Lands l ide
surfaces were often extremely heterogeneous, i.e., bare mineral s o i l versus
rubble versus bedrock versus organic debris and mois t gu l l ies versus dr ier
r idges. In addi t ion, logs and stumps c rea ted t he i r own shaded microsi tes,
T h i s v a r i a b i l i t y meant tha t on ly the most common and abundant species were
repeatedly recorded i n p l o t s within seemingly comparable vegetation. Browsing
by deer may have resu l ted i n the el iminat ion of important indicator species
or , a t l e a s t , reduced the i r ro le . D i f f e rences i n browsing in tens i ty no ted
from area t o area would cause va r ia t i on add i t i ona l t o tha t caused by phys ica l
s i t e cond i t i ons . Reduced access to vege ta t i on f o r deer caused by small
c l i f f s , l a r g e stumps, slash, and debr is a lso cause d i f ferences i n vegetat ive
composition and cover no t d i rec t l y re la ted to the s i tes capac i ty to suppor t
p l a n t growth.
Despite the aforementioned problems, some general trends i n revegetat ion of s l ides are ev ident . The dominant course for revegetat ion on slides is governed by an abundant cover of red alder. On logged areas, the major trend
involves sparse to dense coni fer cover, part icular ly western hemlock and S i tka
spruce. Less commonly, coni fers dominate p a r t i c u l a r p o r t i o n s o f s l i d e s and
red a lder may be an important component o f logged-over areas. Eleven plant
groups were recognized as representing major stages and charac ter is t i cs o f vegetative recovery. Factors involved i n shaping these groups include time
since logging or s l ide fa i lu re , b iogeoc l imat ic zone, and phys ica l and chemical
charac ter is t i cs o f t he subs t ra te i nc lud ing so i l depth, percentage bedrock
exposure, soi l texture, nature of associated rock type, seepage, s o i l
s t a b i l i t y , and degree of surface erosion.
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The f o r e s t p r o d u c t i v i t y o f s l i d e s i s reduced by about 70% when compared
with t h a t o f s i m i l a r l y aged logged stands. This p roduc t i v i t y d i f f e rence
ar ises pr imari ly f rom lower growth rates and stocking of upper s l ide areas and
severe competit ion from red alder i n middle and espec ia l l y lower s l ide
posi t ions. Ear ly height growth of Si tka spruce and western hemlock on s l i des
was about h a l f t h a t i n logged areas. Miles " e t a l . (1984) showed reduct ion i n
height growth of Douglas-f i r on landsl ides o f 38% for t rees up t o 18 years of
age when compared with growth on logged areas. Red alder a lso establ ishes i n
some logged areas but the advance regeneration of conifers seems bet te r ab le
to o f f se t t he rap id g rowth o f a lde r t han does new regenera t ion o f con i fe rs on
slides. Although Sitka spruce production exceeded western hemlock on s l ides,
logged areas s t i l l produce a greater average volume of spruce than s imi lar ly
aged s l ides . Since logged stands over 55 years of age were not sampled, i t was not
poss ib le to d i rec t l y de termine whether a 70% reduct ion i n volume production
would continue t o r o t a t i o n age. However, as revegetation continues and s o i l s
s tab i l ize, product iv i ty on s l ides can be expected t o increase. The t o t a l
volume fo r s l i des 60 years o f age and older (avg . = 85 years) was 498
m /ha. This volume can be compared with the approximately 900 m /ha f o r
second-growth stands of s i t e i ndex 36 m a t 100 years on undisturbed areas a t
the same age (Taylor 1934). The ind ica ted reduc t ion a t 85 years would then be
about 45% for t o t a l volume and 65% for coni fers on ly . Even wi thout act ive
management, product iv i ty on s l ides should recover gradual ly i n subsequent
ro ta t ions . However, Trustrum " e t a l . (1984) pos tu la ted tha t s l ides i n New
Zealand may never reach t h e i r former l e v e l o f product iv i ty . Th is may w e l l be
t r u e f o r t h e upper por t ions of most s l ides .
3 3
Ear ly estab l ishment o f S i tka spruce by p lant ing and a t l e a s t p a r t i a l
c o n t r o l o f red a lder on t h e r e l a t i v e l y s t a b l e and productive lower slopes of
s l i d e s would increase production o f conifers appreciably. I n contrast , the
extreme upper p o r t i o n s o f s l i d e s will suffer from reduced product iv i ty for an
extended period. Establishment or enhancement o f species such as S i tka a lder
(Alnus sinuata) and other n i t rogen-f ix ing p lants should accelerate the
recovery process on these upper slopes.
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5 SUMMARY
1. Debris avalanches change the charac ter o f the te r ra in such t h a t s o i l s on the upper two-thirds of the sl ides are shal lower, coarser, and inc lude
more bedrock exposure than the original soi ls.
2. Though severely perturbed, soi ls on s l i d e s r e t a i n many o f t h e
cha rac te r i s t i cs of t he o r i g ina l podzo l so i l , i.e., h igh organic carbon,
i ron , and aluminum levels. Except for areas of bedrock exposure and very
thin so i ls , revegetat ion on sl ides occurs on secondary (modified) rather
than pr imary soi l mater ia ls. Plant species coloniz ing s l ides are not
markedly d i f f e r e n t from those on adjacent logged stands or o l d growth.
However, greater dif ferences do e x i s t i n p l a n t v i g o r , r e l a t i v e abundance
o f species, and d i s t r i bu t i ona l pa t te rns .
3. The lower ha l f o f recen t l ands l i des i s general ly colonized by red alder,
p a r t i c u l a r l y i n associat ion with calcareous, f ine-textured sedimentary or mixed rock types. Sitka spruce and western hemlock are suppressed by red
alder. When the red a lde r component d e t e r i o r a t e s a t 70-90 years o f age,
the re leased con i fe rs a re o f ten a t suboptimum stock ing leve ls .
4. The upper por t ions o f s l ides a re normal ly f i r s t co lon ized by con i fe rs -- western hemlock mainly, but also Si tka spruce. These con i fe rs exh ib i t re la t ive ly s low growth and a clumped d i s t r i b u t i o n as a r e s u l t o f poor growing conditions. Red a lder may e s t a b l i s h a t a l a t e r stage, provided
m i n e r a l s o i l i s s t i l l exposed, as seed becomes available from maturing
alder lower on the s l ides .
5. Occasional ly, condit ions exist on s l i d e s i n which so i l cond i t i ons a re favorable for t ree growth and where r e d a l d e r f a i l s t o become a serious
competitor. I n these s i tuat ions, s tands cons is t ing large ly of Si t ka
spruce may be very productive.
6. I n comparison with adjacent logged stands i n the same age c lass
(30-59 years), the average slide produces 70% l e s s wood volume.
Pro jec t ions us ing y ie ld tab les fo r o lder second-growth stands and data
from t h i s s t u d y f o r t h e o l d e s t c l a s s o f s l i d e s i n d i c a t e t h a t t h e r e d u c t i o n
- 82 -
a t 85 years would be about 45%. Considering the c o n i f e r component only, reduct ions are calculated a s 72% a t 55 years and 65% a t 85 years.
7. Slow vegeta t ive recovery on slides (48% cover a t 40 years) is as soc ia t ed w i t h upper s lope pos i t ions and espec ia l ly wi th coarse conglomerate and hard volcanic rock types. T h i s slow r ecove ry a l so t ends t o co r re spond wi th a low rate o f red alder colonizat ion. Rapid vegetat ive recovery (83% cover a t 40 years) is as soc ia t ed w i t h lower s lopes and w i t h calcareous and f ine sedimentary rock types.
8. Most spec ie s o f sh rubs and many herbs are severely browsed by deer t h u s reducing their r o l e i n v e g e t a t i v e recovery and possibly lessening their r o l e i n r e s t o r i n g r o o t - r e l a t e d s o i l s t r e n g t h a f te r lands l ides and c l e a r c u t t i n g . Tree s p e c i e s are a l s o s e r i o u s l y damaged by browsing. That western redcedar and yellow cypress are especially u t i l i z e d by deer may partially exp la in why these s p e c i e s are abundant as seed l ings on young slides yet play a m i n o r r o l e i n terms of volume i n o l d e r slides.
9. Despite an exponen t i a l i nc rease i n vege ta t ion and organic sur face cover , h igh b i o l o g i c a l ac t iv i ty on slides -- induced by h i g h s o i l temperatures, low C:N ra t ios , and reduced acidity relative t o n o n - s l i d e s o i l s -- is ins t rumen ta l i n p reven t ing a build-up of humus anywhere near the depths found in l ogged and old-growth stands. Any logging of s tands deve loped on slides should be conducted w i t h care to min imize minera l so i l exposure and the p o t e n t i a l f o r renewed surface s o i l e r o s i o n .
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Mark, A.F., G.A.M. Scott, F.R. Sanderson, and P.W. James. 1964. Forest succession on landsl ides above Lake Thomson, Fiordland. N.Z. 3. Bot. 2: 60-89.
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Poulin, V.A. 1985. A serendip i tous in tegrat ion o f research with management needs: t h e B r i t i s h Columbia F ish/Forest ry In teract ion Program. I n Proc. Workshop on Slope S t a b i l i t y : Problems and Solut ions i n Forest MaEgement, Seatt le, Wash., Feb. 6-8, 1984. D. Swanston (ed i to r ) . U.S. For. Serv. , Gen. Tech. Rep. PNW - 180.
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APPENDIX 2. List of plant species recorded1
Trees
Alnus rubra Bong. Alnus sinuata (Rea.) Rvdb. ”
” ~ ~. .
ChamaecvDarls nootkatehsis (D. . ~~ .
Picea sitchensis (Bong. 1 Carr. Pinus contorta Dougl. Taxus brevi fo l ia Nut t . Thuja p l ica ta Donn Tsuga heterophylla (Raf. Sarg Tsuga mertensiana (Bong. Carr
Don)
Shrubs
Aruncus Sylvester Kostel. Gaultheria shallon Pursh
Ribes bracteosum Dougl. i n Hook. Ribes lacustre (Pers. ) Poir. i n Lam. Ribes laxiflorum Pursh Rubus oarviflorus Nutt . Rubus spec tab i l i s Pursh
~~
Spach
Sambucus racemosa L. ssp. pubens (Michx. ) Vaccinium alaskaense Howell
House
Vaccinium ovalifolium Smith i n Rees Vaccinium parvifolium Smith i n Rees
Herbs
Adiantum pedatum L . ssp. aleuticum (Rupr. ) Calder & Taylor Agrostis ae u i v a l v i s ( T r i n . ) Trin. L- A r o s t i s + alba L. Agrostls exarata Trin. Agrostis scabra Willd. Anaphalis margaritacea (L. ) Benth. & Hook. Aquilegia formosa Fisch. i n DC. Athyrium filix-femina L. (Roth.) ssp. cyclosorum (Rupr.) C. Chr. i n H u l t . Barbarea orthoceras Ledeb. Blechnum micant ( L . 1 With. Botrychium mult i f idum (Gmel. ) Rupr. ssp. Calamagrostis nutkaensis (Presl) Steud. Caltha biflora DC. Campanula alaskana ( A . Gray) Wight : J. P. Cardamine ens lvanica Muhl.: Willd. Carex anthoxan + hea Presl
“ - silaifolium
Anderson
Clausen
Carex Carex Carex Carex Carex Carex Carex Carex Carex
~~
Carex Carex
aurea N u t t . d,Fweyana Schw . dlsperma Dewey
ssp.
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leptopoda (Mackenzie) Calder & Taylor
laeviculmis Meinsh. rnacrochaeta C.A. Meye rnertensii Prescott in obnupta Bailey phyllornanica W . Boott scirpoidea Michx. s tylosa C.A. Meyer viridula Michx.
I Bor
i n
1g
S. Wats.
Cerastiurn vu1 atum L. Cirsium arvense "5- L. ) Scop. 7XEiGii E Z E € y l u m Cronq. Cirsium vulgare (Savi) Airy-Shaw Coptis asplenifolia Salisb. Corallorhiza rnaculata Raf. ssp. mertensiana (Bong. ) Cornus unalaschkensis Ledeb. Cystopter is f ragi l is (L.) Bernh. Dactylis glomerata L. Deschampsia caes i t o s a (L.) Beauv. ssp. berin ensis Deschampsia "k e on a a Hook.) Munro: Bent I+" Digitalis purpurea L. Drosera rotundifolia L. Dryopteris assimilis S. Walker Epilobium delicatum Trel. Epilobium glandulosum Lehm. Equisetum arvense L. Equisetum telmateia Ehrh. Eriaeron oerearinus (Pursh) Greene Fes$uca.okcidktalis 'Hook.. Festuca rubra L. Festuca subulata Trin. in Bong. m t m Michx. Gnaphalium purpureum L. Gnaphalium uliginosum L.
* o h a m . G rnnocar iurn d r o teris (L. Newman
Habenaria saccata Greene Heuchera glabra Willd.: R . & S. Hieracium albiflorum Hook. Holcus lanatus L . Juncus effusus L. Juncus ensifol ius Wikstr. Lactuca biennis (Moench) F Listera caurina Piper Listera cordata (L.1 R.Br. Loliurn perenne L.
'ernald
i n A i t .
Calder
(Hu l t .
* & Taylor
1 Lawr.
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Lolium temulentum L. Luzula multiflora (Retz Luzula parviflora (Ehrh Lycopodium annotinurn L. Lycopodium clavaturn L. Lycopodium inundatum L.
Lejeune Desv.
Moneses Montia 1
Osmorhii Montiaj
Maianthemum - dilatatum (Wood) Nelson & Macbr u n i f m Gray ssp. re t icu la ta 'ontana L. ;iberica-(L. ) Howell ra u r urea (Coult . & Rose) Suksd.
Parnassi; F-7 imbrla a KGnig
i N u t t . ) Calder & Taylor
Pinguicula vulgaris L. ssp. rnacroceras - Poa annua L. Polypodium vulgare L. ssp. " Poa annua L. Polypodium vulgare L. ssp. Polystichum lonchi t is (L. Polystichum ' m K a u l f Prenanthes a m o o k . D
"
occidentale Polystichum lonchi t is (L.) Roth: Roem. Polystichum ' m K a u l f . ) Pres1 Prenanthes a m o o k . ) D. Dietr. Ranunculus repens L. Ranunculus uncinatus D. Don i n G. Do6 Rubus Dedatus Smith
Senecio newcombei Greene Senecio sylvaticus L. Senecio vu1 a r i s L. Sonchus "-5- asDer L. ) Hill Stellaria calycantha Bong. S te l l a r i a c r i spa Cham. & Schlecht. Stel lar ia media (L . 1 Vill. ~~~~ .~ ~~
Streptopus amplexifolius ( L . ) DC. .~
Streptopus roseus Michx. ssp. curv i es Streptopus s t re to oides ( L e d e 4
(Baker " Calder & Taylor
(L ink) Calder & Taylor
(Hook.) Hul t .
(Vail) H u l t . & Rigg ssp. brevipes
Taraxacum off ic ina le Weber i6 Wiggers Tellima qrandiflora (Pur sh ) Dougl. i n Lindl . Thelypteris pheqopteris ( L . ) Slosson i n Rydb. T ia re l l a t r i fo l i a t a L. Tolmiea menziesii (Pursh) T. & G . Tr iental is europaea L. Trifolium repens L. Trisetum cernuum Trin.
~~~ ~~
~ " ~ . ~ .~
Veratrum eschscholtzii A. Gray Veronica americana Schwein.: Be! Veronica serpyl l i fo l ia L. Viola glabella N u t t . i n T. & G .
7th. i n DC.
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Mosses, Liverworts, and Lichens
Atrichum selwynii Aust. Bartramia pomiformis Hedw. Blepharostoma t r i c h o h llum (L. ) Dum. Bl ind ia acuta T" Hedw. B.S.G. Brachythecium asperrimum (C. Muell. ) Buxbaumia p i p e r i Best
Sull.
Calypoqeia sp.
h p h e d w . ) Br id . Ce ha loz ia b icus ida ta (L. ) Dum.
Cladina sp. Cladonia sp. Conoceohalurn conicum (L. 1 Lindb. Dicranel la heteromal la (Hedw . ) ~ Schimp . Dicranum fuscescens Turn. Dicranum majus Turn. Dicranum scooarium Hedw.
~ ~~ ~~
Diplophyllum albicans (L. ) Dum. Drepanocladus aduncus (Hedw . ) Warnst. Fissidens adianthoides Hedw. Fissidens osmundoides Hedw. Hookeria lucens (Hedw. ) Sm. Hy locomium splendens ( Hedw . ) B. S. G . Hypnum c i r c i n a l e Hook. Isopterygium elegans (Brid. ) Lindb. Isothecium s i cu l i f e rum (M i t t . 1 Ren. & Card. Lepidozia r&Dum. Leucolepis menziesi i (Hook.) Steere in L. Koch Metzgeria f m . 1 Dum. Mnium spinulosum B.S.G. Oligotr ichum al igerum Mitt. P e l l i a spp. Pe l t i ge ra spp.
~~
P i lophoron aciculare Ach. Ny l . P lag ioch i la as len io ides (L. Dum. Plagiomnium + insigne Mitt. ) Koponen Plagiothecium undulatum (Hedw . ) 6. S .G. Poqonatum alp<-. Roehl. Pogonatum contortum (Menz. : Br id . ) Lesq. Pohlia nutans (Hedw . Lindb. Polytr ichum commune Hedw. Polytr ichum juniperinum Hedw. Rhacomitrium canescens (Hedw . ) B r i d . Rhacomitrium heterostichum (Hedw. ) Br id . Rhizomnium glabrescens (Kindb. ) Koponen Rhytidiadelphus loreus (Hedw. Warnst. Riccardia SDD.
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Scapania bolanderi Aust.
m m % h r u m Hedw . Stokesiella oregana (Sull. Robins. Tetraphis ellucida Hedw. Tortella tortuosa e”T Hedw.) Limpr.
1 Nomenclature mainly from Hosie (1969) for trees, Calder and Taylor (1968) for other vascular plants, Lawton (1971) for mosses, and Conard and Redfearn (1979) for liverworts.
2 Recorded i n slide 33-5 aer ia l ly seeded i n 1980 with grasses and legumes.
