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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 631.640971 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 Queens 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

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3 7

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12

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29.

30 30

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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

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22

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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). ........................

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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 ......................

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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 ........

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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.

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0 Q, d

I I

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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).

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FIGURE 2. 4 recent, open-slope, debris avalanche.

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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 ) .

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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 (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). 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 ( 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 ; - =

- 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

- 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.

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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

- 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.

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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).

,

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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.

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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.

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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 .

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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.