the long & winding road
TRANSCRIPT
The Long & Winding Road (Regenerating Oaks Naturally)
Patrick Brose
USDA Forest Service
Northern Research Station
Irvine, PA
Acknowledgements
• Many of the details, graphs, and photos, I will present today come from my colleagues.
• Contributors include Bob Long, Aaron Stottlemyer, Gary Miller, Kurt Gottschalk, Tim Frontz, Scott Stoleson, Tom Waldrop, & probably somebody I overlooked.
• So you want to create a new oak forest from an existing one?
• 100-year-old mixed oak stand on a better quality growing site.
• Plenty of red maple poles and saplings.
• No oak seedlings.
• Plan on a 10 to 20 year odyssey of aggravation and frustration.
• WHY?
The Oak Regeneration Process
Flowering
Acorn Development
Seedling Establishment
Seedling Development
Flowering Most oak species begin
flowering between 15-25 years of age in forest stands.
Oaks are monoecious (both flowers on same tree).
Flower buds are formed in mid- to late summer of the previous year.
A number of studies have shown that annual flower crops are surprisingly regular.
So if flower crops are regular, why aren’t there regular acorn crops?
Female flower
Male catkins
ACORN PRODUCTION IN WESTERN
VIRGINIA, 1973 - 1995
0
10
20
30
40
50
60
70
80
90
1973 75 77 79 81 83 85 87 89 91 93 1995
Year
Red oaks White oaks
Flower and Bud Insects
There are at least 46 species of insects that feed on oak buds, flowers, and pollen.
These can reduce flower production, pollen production, and fertilization. Oak treehopper adult
Pollination
Oak pollen is wind dispersed. Maximum pollen dispersal from an individual oak occurs over a 2-3 day period, but the oak pollen season may last 2-4 weeks.
Optimal weather for pollination are warm, dry, breezy days.
Cool, rainy, foggy weather substantially reduces pollen dispersal.
Frost – The MAJOR Weather Problem
Acorn Development Slow at first then embryo growth
accelerates in mid summer (1st year for WO, 2nd year for RO).
Crown size, canopy position, and species are important factors in acorn development.
Acorns are loaded with carbohydrates and fat. Also, some protein and minerals. A popular food for a wide array of insects while they are still in the tree.
WEEVILS - CURCULIONIDAE
INSECTS OF ACORNS
GENUS Curculio
11 EASTERN SPP.
(9+ Attack acorns)
Female chews hole
in acorn and
deposits a single
egg before the
acorns ripen
PHOTO COURTESY FORESTRY IMAGES
WEEVILS - CURCULIONIDAE
INSECTS OF ACORNS
Larvae feed in the acorn for several weeks before cutting
exit holes in the shell
Larvae spend 1-2
years in soil before
pupating
PHOTO COURTESY FORESTRY IMAGES
Major portion of
acorn crop may be
destroyed,
especially if
co-infested by
other insects.
FILBERTWORM – Melissopus latiferreanus
INSECTS OF ACORNS
Female lays
egg on outside
of acorn
Larva bores
into and feeds
on acorn
PHOTO COURTESY FORESTRY IMAGES
GALL WASPS - Callirhytis fructosa
INSECTS OF ACORNS
Stony gall
Gall replaces
the seed
Several larvae
per acorn
PHOTO COURTESY FORESTRY IMAGES
Single larva per gall
Pip Galls caused by
Cynipid Wasp
Callirhytis operator
The galls themselves do not destroy the acorns
Squirrels cut the immature acorns in August and
chew away the edge of the cap to get at the galls.
So that they can feed on the
cynipid wasp larvae inside the
gall.
Other important acorn insects
Weevils of the genus Conotrachelus
Conotrachelus cannot infest a sound
acorn.
Acorn moth – Valentinia glandulella
Valentinia is a secondary invader.
Acorn shell must be damaged.
Weather-Related Acorn Losses
• Generally, weather causes few losses to a developing acorn crop.
• The one exception – drought.
• Oaks will abort acorns to protect against drought-incited decline and mortality.
Gypsy Moth
Aborted acorns due to gypsy moth defoliation
Effect of Gypsy Moth Defoliation Level on
Sound Acorn Biomass Production (McConnell 1988)
0
100
200
300
400
None Moderate Heavy
1986
1985
Defoliation Level
Pou
nd
s p
er A
cre
Effect of Gypsy Moth Defoliation Level on
Total Acorn Production (McConnell 1988)
Aco
rns
per
Acr
e (1
00
0's
)
Fully Developed
Partially Developed
Undeveloped
Defoliation Level
0
100
200
300
400
500
600
700
None Moderate Heavy
Acorn Production in a Mature Mixed Oak Stand
Huntingdon County, Penn. Game Commission (1995)
19
68
1
96
9
19
70
1
97
1
19
72
1
97
3
19
74
1
97
5
19
76
1
97
7
19
78
1
97
9
19
80
1
98
1
19
82
1
98
3
19
84
1
98
5
19
86
1
98
7
19
88
1
98
9
19
90
1
99
1
19
92
1
99
3
19
94
0
100
200
300
400
500
600
Year
Pou
nd
s p
er
Acr
e
White Oaks
N. Red Oak
Other Red Oaks
(Years with Defoliation)
The Acorn → Seedling Transition
Forest Floor Obstacles to Establishing Oak Seedlings
• Optimal seedbed is a thin O horizon (litter & rootmat).
• In this environment, an acorn is easily buried and can get the radicle into mineral soil.
• If litter and/or rootmat are > 2 inches thick, then these become obstacles to oak seedling establishment.
Insects and diseases will kill
recently-fallen acorns • A study of the 2001 acorn
crop at Clear Creek SF in northern PA found that 33% of the acorns became infested or infected after they were on the ground.
Weather too
• Acorns must maintain 30 – 50% moisture content to remain viable.
• That same study found that nearly 50% of the acorns were killed by desiccation during the 2001-02 winter (cold, dry, & windy with little snow).
Fire too
Several studies report 40 to 90% loss of viable acorns to fire.
Acorns as Wildlife Food Wildlife known to eat significant amounts of
acorns:
Acorns in Wildlife Diets
• At least 90 species eat acorns in Mid-Atlantic region.
• The MAJOR hard mast source since the loss of the
American chestnut.
• So important that mast crops significantly affect
wildlife behavior.
• Numerous studies report wildlife consume from 5 to
95% of an acorn crop.
How Do Acorns Avoid Bugs, Crud, Desiccation, Fire, & Wildlife?
• With a little help from some friends.
• Blue jays and tree squirrels are scatter hoarders.
• They bury single acorns in edge areas and areas with thin leaf litter.
NRO Germination Rates
0
10
20
30
40
50
60
70
80
90
100
110
120
L L/F L/HC L/F/HC B B/F B/HC B/F/HC
Ger
min
ati
on
Ra
te (
%)
Treatment
A
B
Oak Seedling Soil Requirements
• Forest floor and underlying mineral soil are both important, but often overlooked or minimized.
• Generally, oak seedlings grow fastest when there is adequate soil moisture and soil nutrients.
• Their exact needs are not well researched in forest environments.
Oak Seedling Soil Requirements • Ectomycorrhizae are essential for oak
seedling survival.
• Low soil pH and lack of soil calcium and magnesium (Acidic Deposition) implicated in loss of ectomycorrhizae and poor seedling growth.
• Long et al. 2012 COULD NOT substantiate the calcium & magnesium theory in a detailed, replicated study.
• Other soil nutrient needs not well researched in forest environments.
• New oak – soil research underway on Tuscarora SF.
Seedling Root Diseases
• Damping-off fungi Pythium
Rhizoctonia
Phytophthora
Cylindrocladium
• Root rotting fungi Armillaria spp.
These attack and kill new germinants
Seedling Foliage Diseases
Oak anthracnose • This group of diseases
are “compound interest” diseases with repeated cycles of spore production and infection if weather conditions are favorable (a cool, wet spring).
• In those years, an entire cohort of seedlings can be killed by anthracnose
Losses to Small Mammals • New seedlings are
clipped off just above the ground. Top of seedling is NOT eaten. Happens during the early summer.
• Looks like cutworm damage of vegetables.
• Seems to occur most frequently in areas with abundant woody debris.
• Not sure who the culprit is. In CA, gophers and voles kill thousands of oak seedlings in this manner.
Losses to Weather • Two major sources.
• Late frosts damage or kill the
newly emerged leaves. Oak seedling does not yet have the root reserves to sprout from basal buds.
• Drought can wipe out new oak seedling cohorts before they have developed root systems and stress well established seedlings.
• Effects of both can linger for several years.
Fire • Small oak seedlings are
virtually defenseless against fire because they haven’t yet developed their root systems.
• Growing-season fires (after leaf expansion) are especially devastating to small oak seedlings.
Reality Check
• Up to this point in the regeneration process, losses of acorns and oak seedlings can be small or substantial.
• However, substantial losses to these factors are often localized and temporary.
• Consequently, many oak forests will have a pool of small oak seedlings that continually recycles.
• The “BIG” oak regeneration problems are about to begin.
The BIG 3 (CDL)
Excessive Deer Browsing
Competition from other hardwoods and interfering vegetation
Not Enough Light
Seedling → Competitive Reproduction Transition
• Growing oak seedlings to a competitive size is the MAJOR bottleneck in the oak regeneration process for much of the eastern United States.
• Involves growing oak root systems.
• Competitive size and oak root development are highly dependent on sunlight, site quality, composition of competing species, and deer browsing.
Sunlight Effects on NRO Root Development
0
5
10
15
20
25
1 2 3 4 5 6 7 8
Ro
ot
Co
lla
r D
iam
eter
(m
m)
Years Since Planting
¼ inch
¾ inch
½ inch
1 inch
5% Sun
15% Sun
50% Sun
Full Sun
Sunlight Effects on Roots of Other Oaks
0
5
10
15
20
25
1 2 3 4 5 6 7 8
Ro
ot
Co
lla
r D
iam
eter
(m
m)
Years Since Planting
¼ inch
¾ inch
1 inch
½ inch
5% Sun
15% Sun
50% Sun
Full Sun
Sunlight Effects on Oak Seedling Growth
Sunlight Effects on Oak Seedling Growth
At 15% sun, oaks are small, but so too are the competitors (maple).
At full sun, oaks are tall, but only half the height of the competitors (birch).
Deer Can Slow Or Stop Oak Seedling Development
What? Don’t blame me,
its those darn coyotes’ fault!!!
0
20
40
60
80
100
120
2002 2003 2004 2005 2006 2007 2008 2009
Pro
po
rtio
n o
f S
urv
ivin
g S
eed
lin
gs
(%)
Control Shelterwood
Fence Fence + Shwd
Sunlight & Deer Effects on Oak Seedlings
56%
28%
24%
2%
Brose, Northwest PA Study
Sunlight & Deer Effects on Oak Seedlings
0
10
20
30
40
50
60
70
80
90
100
0 1 2 3 4 5
Years since treatment
Perc
en
t Herbicide
& Fence
Herbicide
Control
Fence
67%
14%
36%
23%
Gary Miller, WV Study
Deer Effects on Oak Seedling Growth
0
0.1
0.2
0.3
0.4
0.5
High Medium Low Control
Feet
Amount of Sunlight
Fenced
Unfenced
Gary Miller, WV Study
The Oak Regeneration Process
10 to 20 years
Can we do anything to speed up the process?
Make Use Of Oak Stump Sprouts
• Bypass the flowering, acorn development, and seedling establishment stages of the oak regeneration process and all their associated pitfalls.
• But, they come with their own set of regeneration problems.
Obstacles to Oak Coppice Silviculture
Not all oak stumps sprout
Prone to ice, snow, and wind damage Weak attachment
Subject to several foliar diseases
Deer love to eat them
Grow Oaks Where They Want To Grow (Dry Sites)
• The regeneration process is already underway (oak seedlings present).
• Generally, the drier sites do not have as severe of competition/interference issues as moister sites.
• Dense shade is less prevalent.
• Oak seedlings achieve “competitive” status at smaller sizes.
Dry Site Obstacles
• While this approach does potentially sidestep some of the oak regeneration obstacles, it still can encounter many of them.
Thick Duff
Bugs & Crud
Deer
Mountain laurel
Use Artificial Regeneration
QUESTIONS (ON NATURAL OAK REGENERATION)