Predicting behavior
of forest diseases
as climate changes
A webinar sponsored by USDA Forest Service,
Western Wildland Environmental Threat Assessment Center
& Pacific Southwest Research Station;
University of California Cooperative Extension, Marin County;
and University of California, Santa Barbara
Welcome and overview
• Who we are
• Who you are
• Tips for participants
– PHONE: Turn off computer speakers, mute
the phone, don’t place any holds
– COMPUTER: Turn on computer speakers
– Maximize your web browser to full screen
– Submit questions through “Chat (Q & A)”
box on left side of screen
Agenda
Jim Worrall
• Case study: Cytospora canker of alder
Jim Worrall, USDA-Forest Service
• Case study: Alaska yellow cedar decline
Paul Hennon, USDA-Forest Service
• Case study: Sudden aspen decline
Paul Hennon
Jim Worrall, USDA-Forest Service
• Case study: Swiss needle cast
Jeff Stone, Oregon State University
• Management considerations & conclusions
• Questions and answers
Jeff Stone
Janice Alexander, UC Cooperative Extension
Introduction to
climate change
and forest diseases
Modified from a presentation by Alex Woods, BC Forest Service, Smithers BC, Canada; Photo by H. Kope
Alaska yellow cedar decline; Photo by P. Hennon
Fuel Wood
Biodiversity
Non-wood
Forest Products
Climate
Regulation
Industrial
Wood
Resource
Biospheric
Water
Protection
Soil
Protection
Spiritual
Forest
Services
Ecological
Amenities
Health
Protection
Cultural
Historical
Social
Sports
Ecotourism
Fishing/Hunting
Recreation
Millennium Ecosystem Assessment 2005
Disease:
Any deviation in the normal functioning of a
plant caused by some type of persistent biotic
or abiotic agent. (Manion 1981)
Red band needle blight, Dothistroma in British Columbia, Canada
Disease Triangle
Figure courtesy of: Stevens RB, 1960. In Horsfall JG, Dimond, AE, eds. Plant Pathology,
an Advanced Treatise. Vol. 3. New York: Academic Press, 357-429.
Photo credit: Jessie Micales Glaeser, US Forest Service
Sudden Oak Death (Phytophthora ramorum) near Big Sur, Monterey Co., CA
Swiss needle cast on a Douglas-fir needle
Climate Change:
"a change of climate which is attributed directly or
indirectly to human activity that alters the composition
of the global atmosphere and which is in addition to
natural climate variability observed over comparable
time periods.”
United Nations Framework Convention on Climate Change
Disease Triangle under the influence of Climate Change
z
Environmental
factors
UNPREDICTABLE
RESULTS
z
Pathogen and its
epidemiology
z
Host availability
ENVIRO
NMENT
Cytospora canker of alder
Yellow cedar decline
Sudden aspen decline
Swiss needle cast
Thinleaf Alder
Jim Worrall
A long
-standing
long-standing
epidemic of Cytospora canker
tied to summer heat
US Forest Service
Rocky Mountain Region
Gunnison, Colorado
Alnus incana ssp. tenuifolia
•
Thinleaf alder
•
Family Betulaceae
•
Large shrub or tree
to ~10 (15) m
•
Sprouting Æ small
clumps/clones
•
From Arctic Ocean
to Mexico border
•
Important riparian
species in Southern
Rockies
Survey of northern New Mexico,
Colorado, and southern Wyoming
Condition of all stems
Stem condition class
% of 6,503*
standing stems
Live, no dieback
34%
Live, with dieback
29%
Dead
37%
* 68 transects, 859 genets
Genet Condition Index
⎛ d + (0.5 • s ) ⎞
GCI = ⎜
⎟ • 100
⎝ d +s+h ⎠
where:
d = number of dead stems
s = number of stems with dieback
h = number of healthy stems
Cytospora canker
of alder
• Occurs as
– Long, narrow stem
cankers
– Shoot blight
– Branch cankers
• Abundant fruiting
• Girdles and kills
branches and stems
Epidemic began before
1991
– 1991 Wyoming requested visit
– Unusual alder mortality along Big
Laramie River
– A Wyoming forester had also seen
mortality
• Along Tomichi Creek near Gunnnison, CO
• North of Kremmling, CO
• South Fork of Rio Grande, CO
• Lamar River, northeast of Yellowstone NP
– Attributed to Cytospora canker
– Another report noted it in 1996,
concern raised in 2001, 2002
Why the epidemic?
• Cytospora canker certainly the proximal cause of
the mortality, but:
– Such diseases usually kill stressed trees
– Why would a presumably native pathogen cause
such a long-term and severe epidemic?
Measured canker growth
• Objective:
– Determine expansion rate
– Determine season of
expansion
• Marked about 75 cankers
• Monitored and remeasured
for various periods
Canker
growth
• Most cankers
grew and killed
host within one
year of marking
• Canker growth
rates highly
variable
Weather
• Up to 50
cm/month in one
direction
• Most growth
occurs during
midsummer at
hottest time of
year
Long-term
cyclic variation of
summer heat
Spectral analyses of
summer heat index in
Gunnison
• Dominant, significant
cycle with period 21 yr
• Amplitude decreasing
Temperature cycles Æ epidemic cycles?
• Oscillating summer temperatures
may explain periodic epidemics
– Epidemics during positive
phases, recovery during negative
phases?
– No long, cool “recovery” period
since 1976
• But recent climatological
analyses of Colorado also show
increasing trend . . .
Increases in annual mean temperatures
y In Colorado, statewide temperatures have increased
about 2°F over 30 years.
y In regions of Colorado, widespread warming is evident
across most climate divisions in the 30-year period.
y Began 1960-70.
Ray AJ, Barsugli JJ, Averty KB. 2008.
Climate Change in Colorado: A Synthesis to
Support Water Resources Management and
Adaptation. Cooperative Institute for
Research in Environmental Sciences,
Western Water Assessment, Boulder,
Colorado. 52 pp.
Management
• No research on
management
• Remove old stems,
regenerate clones?
– revitalize clones
– reduce inoculum
• Effective?
How long?
• Riparian areas present
management issues
Conclusion
„
High summer temperature appears related to
Cytospora canker in alder
„
Current epidemic since late 1980s or earlier, 2/3 of
standing alder dead or diseased.
„
Historically, oscillating summer temps may have
led to cycle of epidemic and recovery of alder
populations
„
More recently, temperature trend has dominated
„
If trend continues, already severe epidemic will
likely become more damaging, with no opportunity
for recovery.
„
Management may not be practical without
addressing environmental factors involved.
Worrall JJ. 2009. Dieback and mortality of Alnus in the Southern
Rocky Mountains, USA. Plant Disease 93(3): 293-298.
Worrall JJ, Adams GC, Tharp SC. 2010. Summer heat and an
epidemic of cytospora canker of Alnus. Canadian Journal of
Plant Pathology, 32(3): 376-386.
Yellow-cedar Decline: Shifting Climate,
Altered Niche, and a Dynamic Conservation Strategy
Paul Hennon, Dave D’Amore, USFS, Pacific Northwest Research Station, Dustin Wittwer, S&PF
Paul Schaberg, USFS, Northern Research Station, John Caouette, Colin Shanley, TNC
Yellow-cedar, Alaska yellow-cedar
Callitropsis (Chamaecyparis) nootkatensis
Commercial value
Cultural value
Ecological value
Range map
Cedar values Æ incentives to alter conservation and management
Scenario to explain tree death
Topography, soils
1
Wet soils
1,6
Open canopy conditions
1, D’Amore and Hennon 2006
2, Beier et al. 2008
3, D’Amore et al. 2009
4, Schaberg et al. 2005
5, Schaberg et al. 2008
6. Hennon et al. 2010
7. Schaberg et al. in review
6
3
Exposure
6
Snow
6
Soil warming, spring
Snow
4
Shallow Freezing Dehardening
roots
7
2,5
< -5°C
4
Root freezing injury
32
Scenario to explain tree death
Climate:
Topography, soils
1
Wet soils
Predisposing,
1,6
Open canopy conditions
3-4,000y
6
3
Exposure
6
Snow
6
Soil warming, spring
Snow
Inciting,
weeks
4
Shallow Freezing Dehardening
roots
7
2,5
4
Root freezing injury
Proximal,
days
Yellow-cedar decline
200,000 ha in AK
>50,000 ha in BC
Pattern: latitude x elevation
Onset ~ 1900
Broad-scale
Cedar
decline
Low
snow
Snow accumulation (4 zones) based
on Prism analysis, The Nature
Conservancy, Dave Albert, Juneau
Protective role of snow
Cedar decline distribution
35 from
Aerial detection surveys
1961-1990
Mount Edgecumbe
Snow Model
Current
cedar
decline
Inadequate
snow
Protective
snow
36
CGCM2_B2X
2080
37
Bioclimate envelope – Climate space – Climate profile
Migration
New habitat
Existing habitat
(Healthy)
Adapted
“stable”
Existing habitat
(Dead/dying)
Maladapted
Yellow-cedar’s ecological niche
30
Yellow-cedar
Western
hemlock
Basal area (m2 ha-1)
25
20
15
Mountain
hemlock
10
Sitka
spruce
Shore
pine
5
0
0
20
40
60
80
Understory ordination score
Poorly-drained
Bog
Well-drained
Forest
39
Yellow-cedar’s ecological niche
Unsuitable Suitable
Yellow-cedar
80
Western
hemlock
Basal area (m2 ha-1)
25
60
20
15
40
Mountain
hemlock
10
Sitka
20
spruce
Shore
pine
5
Yellow-cedar dead (%)
30
0
0
0
20
40
60
80
Understory ordination score
Poorly-drained
Bog
Well-drained
Forest
40
Embedding cedar’s niche in climate envelopes
Migration
Adapted “stable”
Maladapted
Modeling for suitable/unsuitable
cedar habitat
Snow
(dynamic)
Soil drainage
(~stable)
A Dynamic Conservation / Management Strategy
for Yellow-cedar
In healthy forests
In declining forests
Climate
Maladapted
Climate
Adapted
43
A few lessons from the cedar case study:
• Multidisciplinary research to address complexity
• Spatial – temporal patterns as clues
• Importance of site factors
• Crossing an environmental threshold (rain - snow)
• Autecology, unique vulnerabilities (-5°C lethal to roots)
• Need for dynamic conservation strategies
44
Sudden Aspen Decline and Climate Change
Jim Worrall
US Forest Service
Rocky Mountain Region
Gunnison, Colorado
Mancos‐Dolores District,
San Juan NF
2006
Photos by Phil Kemp
Near Gunnison 2006
Photos by Dave Kinateder
Sudden Aspen Decline (SAD)
•
SAD characterized by: – Rapid, synchronous branch dieback and mortality
– Landscape scale (not stand scale)
– Secondary (not primary) insects and pathogens
•
In Colorado
– Peak area in 2008: 542,000 acres (>17% of cover type)
– 1,078,000‐acre footprint since 2003
•
Also in southern WY, and similar damage in northern AZ, southern UT, AB, SK
•
Spread seems to have stopped now, but some affected areas continue to worsen
Elevation distribution of aspen and SAD
Aspect in 3 elevation classes
Grand Mesa NF
Polygon indicates relative frequency of aspects in 20‐degree classes
Line indicates slope‐weighted mean aspect and r
Green is healthy, red is dead
50
Higher slope positions Æ more SAD
Recent crown loss (%)
40
30
20
10
Summits have significantly higher crown loss than toeslopes
0
SU
SH
BS
Slope position
FS
TS
Regeneration not increasing with overstory death
Live aspen regen. (103 stems ha-1)
25
20
Average regeneration one year after clearcutting aspen in SW Colorado: 76,600 ha‐1
R2 = 0.0008
P = 0.71
15
10
5
0
Average regen. in 0
uncut, intact stands in SW Colorado: 2,500 ha‐1 (Crouch 1983)
20
40
60
Recent crown loss (%)
80
* Regeneration = stems up to 12 cm DBH
100
Roots dying in many SAD stands
25
Live roots
Dead roots
Mean # of roots
20
15
10
Both live and dead roots differ significantly between healthy and damaged plots
5
0
Healthy plots
Damaged plots
SAD and the 2002 Drought
•
SAD severe on:
–
–
–
–
–
–
•
•
Low elevations
South/west slopes
Upper slope positions
Low site index
Low basal area
Dry vegetation types
All related to
moisture/site
quality
In Colorado, SAD appeared in 2004, two yr after severe “global‐change‐type drought”* (dry AND hot)
Climate moisture index
– In 2002, aspen that developed SAD had greater moisture deficit than aspen that remained healthy
– SAD first appeared where the greatest deficits, and the greatest difference between healthy and damaged, occurred
* Breshears, et al. 2005. Regional vegetation die‐off in response to global‐change‐
type drought. Proc. National Academy Sciences USA 102, 15144‐15148.
SAD and the 2002 Drought
• Rehfeldt et al. (2009) found:
– 2002 had the most extremely unfavorable climate for aspen in the record
– Sites where SAD is occurring are at the fringe of aspen’s climate niche
– Lower elevation of climate suitable for aspen expected to rise 2,450 ft by 2090
– In CO, 2/3 of sites currently suitable for aspen projected unsuitable by 2060
• Thus the 2002 drought:
– was similar to events anticipated more frequently under climate change
– had impacts consistent with those predicted from climate change
Rehfeldt, G.E., Ferguson, D.E., Crookston, N.L., 2009. Aspen, climate, and sudden decline in western USA. For. Ecol. Manag. 258, 2353‐2364.
Recent climate suitable for aspen
(per climate profile models by Rehfeldt et al. 2009)
Recent climate suitable for aspen
with aspen cover type
Recent climate suitable for aspen with aspen cover type plus SAD
Climate suitable for aspen in 2060, using 3 global climate models
(modeling by Rehfeldt et al. 2009)
Climate suitable for aspen in 2060, with recent SAD
(modeling by Rehfeldt et al. 2009)
On SJNF, 92% of SAD occurred where all models agree, the climate will be unsuitable for aspen in 2060
Some considerations about the future
• Climate and distribution projections are uncertain
• SAD does not appear to be spreading much since 2008
• If SAD is a harbinger of climate change, it will probably occur in spurts, NOT at a steady rate
• The forest and forest diseases will respond to climatic extremes, NOT to the means.
Management Questions
• Possible management responses – should we:
1. Abandon management where climate is predicted to be unsuitable?
ƒ If so, how far into the future should we look?
2. Manage to increase resilience in those areas?
ƒ Young stands (≤ 40 yr old) were not affected by SAD
3. Focus on managing where aspen has a more certain future, reducing conifer encroachment?
• Where the future will be unlike the past, is the concept of “restoration” no longer useful?
Worrall JJ, Egeland L, Eager T, Mask RA, Johnson EW, Kemp PA, Shepperd WD. 2008. Rapid mortality of Populus tremuloides in southwestern Colorado, USA. For. Ecol. Mgmt. 255:686‐696.
Worrall JJ, Bethers S, Egeland L, Mask R, Eager T, Howell B. 2010. Effects and etiology of sudden aspen decline in southwestern Colorado, USA. For. Ecol. Mgmt. 260:638‐648.
Swiss Needle Cast
Jeff Stone
Oregon State University
Dept. of Botany & Plant Pathology
Plant Pathogens and Climate Change
Plant pathogens and insect pests may be much more
sensitive to microclimatic changes than their host
plants
Insect and disease cycles are more sensitive to annual
weather variation than their hosts
Insects and plant pathogens have shorter generation times,
so evolutionary response to climate change is faster
Insects and plant pathogens can be important factors
limiting the geographic distribution of their host species
Climate change, acting through plant pathogens and insect
pests will likely result in changes in geographic
distributions of important crop and forest species
Forestry Crops and Climate Change
Forestry crops are particularly vulnerable to climate change
mediated effects by pathogens and insects because:
Time between planting and harvest may be 40 - 60 years, or more,
for forest crop species.
At current rates of climate change in northwestern North America,
estimated at about 0.5º C per decade, prevailing conditions
affecting tree pathogen and insect populations will change
significantly between planting and harvest of forest crops.
Forest diseases that are most likely to be affected by climate
change are those that are demonstrably affected by weather.
Swiss needle cast, a forest disease affected by climate
chlorosis
needle abscission
reduced growth
diseased
healthy
The Pathogen: Phaeocryptopus gaeumannii
pseudothecia
pseudothecia
pseudothecia
Disease is caused by occlusion of stomates
Fruiting bodies of the fungus block
stomates
Gas exchange is impaired, reducing net
CO2 assimilation
Reduced Anet coincides with formation of
ascocarp primordia
12
Control
Infected
Net Assimilation Rate
(μmol CO2 m-2 s-1)
Pseudothecia emerge
10
8
6
4
2
guard cells
t
c
v
Oc N o D e
r
r
y
n
n
b
Ja Fe Ma Ap Ma Ju
Sample Date
Manter et al. 2000
Relationship between proportion of stomata
occluded, Anet and needle retention
1000
A
B
800
Anet (g m-2)
600
400
200
0
-200
-400
-600
-800
if Anet > 0
2
R2 = 0.789
y = 6.29x
R = 0.985
y = 648 - 34.6x + 0.213x2
0
20
40
60
Pseudothecia Density (%)
0
20
40
60
80
100
Needle Retention
(%, April 2000)
The greater the number of fruiting bodies on a needle and the lower the needle retention,
the less photosynthesis (CO2 uptake).
Decreased CO2 uptake results in premature loss of foliage.
If about 25% of stomates are blocked, net CO2 uptake is zero.
Manter et al. 2003 Ecological Modelling 164: 211-226
The less foliage on the tree, the less the volume growth
Normal needle retention, 3.9 years
2.5 years of foliage, volume growth reduction of up to 14-30%
1.6 years of foliage, volume growth reduction of 30-50%
Maguire et al. 2004, Swiss needle cast cooperative annual report
Predicting Swiss Needle Cast Severity
The best predictors of P. gaeumannii abundance and disease
severity are mean daily winter temperature and spring leaf wetness,
because of their effects on infection and pathogen growth
one-yr needles
two-yr needles
Climate-only model:
Predicted Infection Index
0.4
0.3
0.2
0.1
R2=0.794
0.0
0.0
0.1
0.2
0.3
O bserved Infection Index
0.4
Predicted (line) vs. observed
values for abundance of P.
gaeumannii on one- and twoyear-old needles for sites in the
Coast Range, based on winter
(Dec-Feb) average daily
temperature, spring leaf
wetness.
The abundance of P. gaeumannii is closely
correlated with foliage retention
Relationship between predicted and actual
colonization index (CI), NZ sites
20
e
lin
1
:
1
(a)
Relationship between model
prediction and observed P.
gaeumannii abundance (CI) for
one-year-old needles
Predicted CI
15
10
5
CI = -8.56 + 2.68 Tav june
R2= 0.82
0
-5
-5
0
5
10
15
20
Actual CI
(b)
l
1:1
Predicted CI
30
ine
Relationship between model
prediction and observed P.
gaeumannii abundance (CI) for twoyear-old needles
20
10
CI = -24.06 + 7.44 Tav june
0
R2 = 0.75
0
10
20
Actual CI
30
By using high resolution PRISM spatial climate
models it is possible to make spatial
predictions about distribution of disease
severity based on current climate and
topography
Predicted change in
Swiss needle cast
severity in New Zealand
A, E: Current distribution
D: Projected distribution
under MIROC A2 by
2040
H: Projected distribution
under MIROC A2 by
2090
By 2090 loss of 36 - 65%
of land area suitable for
Douglas-fir
Changes in SNC severity in western Oregon under climate change
Oregon coastal
SNC epidemic
zone
Current area
predicted to have
<60%
foliage retention
based on current
decade climate
averages
3,682 sq km
Predicted
change in land
area with
<60% foliage
retention by
2090
MIROC A2
climate model
7,184 sq km
Managing Swiss Needle Cast
Foliar fungicides?
Effective, but not cost-effective
Short duration of control
Environmental concerns
Alternative species?
In SNC zone favor alternatives to
Douglas-fir, western hemlock, western
redcedar, sitka spruce
Mixed species?
In SNC zone all Douglas-fir is affected,
even in mixed stands
Genetic resistance?
All Douglas-fir seed sources are
susceptible to SNC
Some families grow better than others,
tolerance
No immune genotypes known
QuickTime™ and a
decompressor
are needed to see this picture.
Managing Swiss Needle Cast
Plan for climate change!
SNC severity will change with changing climate
SNC likely will not decrease in current epidemic zone
Epidemic zone may expand in next 40 - 60 years
Monitor
Understand disease impacts
Tools for estimating disease severity, growth impacts
available through OSU extension
Silviculture
Thinning does not increase disease severity
Use planned thinning to reduce % Douglas-fir if
disease levels are high
Management of forest diseases
given climate change
• Monitoring
• Forecasting
• Planning
• Mitigating strategies
Management of forest diseases
given climate change
(1) Monitoring
Management of forest diseases
given climate change
(2) Forecasting
(3) Planning
Management of forest diseases
given climate change
(4) Adaptation
and mitigation
• Reducing other stresses
• Control invasive species
• Reduce forest fragmentation
• Consider both historical and
projected climate
Photo credit: US Forest Service Region 5
Conclusions, part I
Host
Pathogen
Environment/
Climate
Host
Pathogen
Environment/
Climate
Conclusions, part II
• Species on the edge are at greatest risk –
look at the extremes
• Need a baseline knowledge of current
conditions for future monitoring and
comparisons
• Expect change and plan for uncertainty
• Share!
Questions and Answers
Photo credit: Jessie Micales Glaeser, US Forest Service
Further reading
Beier, C.M.; Sink, S.E.; Hennon, P.E.; D'Amore, D.V.; Juday, G.P. 2008. Twentieth-century warming and the dendroclimatology of declining yellow-cedar forests in
southeastern Alaska. Can. J. For. Res. 38: 1319-1334.
Black, B. A. , Shaw D. C., Stone, J. K. 2010. Impacts of Swiss needle cast on overstory Douglas-fir forests of the western Oregon Coast Range. Forest Ecology
and Management 259:1673-1680.
D’Amore, D.V.; Hennon, P.E., Schaberg, P.G., Hawley, G. 2009. Adaptation to exploit nitrate in surface soils predisposes yellow-cedar to climate change-induced
decline while enhancing the survival of redcedar: a new hypothesis. Forest Ecology and Management. 258: 2261-2268.
Hennon, P.E.; D’Amore, D.; Wittwer, D.; Caouette, J. 2008. Yellow-cedar decline: conserving a climate-sensitive tree species as Alaska warms. In: Deal. R., ed.
Integrated restoration of forested ecosystems to achieve multiresource benefits: proceedings of the 2007 national silviculture workshop. Gen. Tech. Rep. PNW-GTR-733.
Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. Pp. 233-245.
Hennon, P.E.; D’Amore, D.V.; Wittwer, D.T.; Lamb, M.B. 2010. Influence of forest canopy and snow on microclimate in a declining yellow-cedar forest of
Southeast Alaska. Northwest Science 84: 74-87.
Kliejunas, John T.; Geils, Brian W.; Glaeser, Jessie Micales; Goheen, Ellen Michaels; Hennon, Paul; Kim, Mee-Sook; Kope, Harry; Stone, Jeff; Sturrock, Rona; Frankel,
Susan J. 2009. Review of literature on climate change and forest diseases of western North America. Gen. Tech. Rep. PSW-GTR-225. Albany, CA: U.S.
Department of Agriculture, Forest Service, Pacific Southwest Research Station. 54 p.
Manter, Daniel K., Paul W. Reeser, and Jeffrey K. Stone. 2005. A Climate-Based Model for Predicting Geographic Variation in Swiss Needle Cast Severity in the
Oregon Coast Range. The American Phytopathological Society, DOI: 10.1094/PHYTO-95-1256.
Schaberg, Paul G., Paul E. Hennon, David V. D’Amore and Gary J. Hawley. 2008. Influence of simulated snow cover on the cold tolerance and freezing injury of
yellow-cedar seedlings. Global Change Biology 14: 1–12. doi: 10.1111/j.1365-2486.2008.01577.x
Stone J. K., L. B. Coop, and Daniel K. Manter. 2008. Predicting effects of climate change on Swiss needle cast disease severity in Pacific Northwest forests.
Canadian Journal of Plant Pathology 30:169-176.
Watt, M. S., Stone, J. K., Hood, I. A. and Palmer D. J. 2010. Predicting the severity of Swiss needle cast on Douglas-fir under current and future climate in New
Zealand. Forest Ecology and Management (in press).
Welsh, C., K. Lewis and A. Woods. 2009. The outbreak history of Dothistroma needle blight: an emerging forest disease in northwestern British Columbia,
Canada. Can. J. For. Res. 39: 2505–2519.
Woods AJ, Heppner D, Kope H, Burleigh J, and Maclauchlan L. 2010. Forest Health and Climate Change: A British Columbia perspective. Forestry Chronicle 86:
412-422.
Worrall, JJ, GC Adams, SC Tharp. 2010. Summer heat and an epidemic of cytospora canker of Alnus. Canadian Journal of Plant Pathology 32 (3): 376-386.
Worrall, James J., Suzanne B. Marchetti, Leanne Egeland, Roy A. Mask, Thomas Eager, and Brian Howell. 2010. Effects and etiology of sudden aspen decline in
southwestern Colorado, USA. Forest Ecology and Management 260: 638–648.
Final words
• Any remaining questions can be sent to
Janice who will post answers in this
meeting room along with the recording
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