Changing the climate, changing the rules:
global warming and insect disturbance in western
North American forests
Allan L. Carroll
Canadian Forest Service
Pacific Forestry Centre
Victoria, BC
Natural Resources Ressources naturelles
Canada
Canada
Canada
Synopsis
Ù Potential effects of CC on herbivorous forest
insects and their role as disturbance agents
Ù CC versus natural variability versus anthropogenic
modification of forest ecosystems
Ù General framework: assessing CC impacts on insect
disturbance
Ù Examples
Ù Conclusions
Timber volume (m3) lost per year (×106)
Relative impacts of disturbance types in northern forests
Ù Disturbance affects large
areas of boreal and subboreal forests
200
150
Ù Herbivorous insects (and
diseases) ≈4× greater
impacts than wildfire
100
Ù (Harvesting most significant
source of disturbance)
50
0
g
in
st
ve
e
ar
H
as
se
di
s/
ct
se
In
e
fir
ild
W
Source: National Forestry Database 1995
Insects as ectotherms
ÙAll aspects of life histories
determined by temperature
ÙRapid responses to changing
climate
ÙEvidence to date:
• Behavioral shifts
• Genetic expression
• Range expansion
Potential effects of global warming on
herbivorous insects
Pros
Ù Reduced winter mortality
Ù Increased thermally benign
habitat
Ù Reduced host resistance
Ù Escape from
competitors/predators
Ù Increased host range
Cons
Ù Phenological asynchrony
Ù Reduced thermally benign
habitat
Ù Shift/depletion of hosts
Ù Competition/predation from
invasive species
Ù Dispersal costs to new
habitats
Potential effects of global warming on insect
disturbance
Ù Altered outbreak frequency/duration
Ù Modified herbivory/damage rates
Ù Range expansion/contraction
Ù Novel host species associations
Recent climatic trends (western Canada)
Mean temperature increases since 1950
Trend in annual precipitation since 1950
Source: Environment Canada, Adjusted Historical Canadian Climate Data. 2004.
4000
4000
2000
2000
00
Mapped outbreak area (ha × 1033)
6000
6000
Mapped outbreak area (ha × 1033)
Mapped outbreak area (ha × 1033)
400
400
Mountain pine beetle
2500
2500
1000
1000
2000
2000
1500
1500
1000
1000
500
500
00
0000
2200
9900
1199
8800
1199
7700
1199
6600
1199
5500
1199
4400
1199
3300
1199
2200
1199
1100
1199
Spruce beetle
300
300
200
200
100
100
00
800
800
Western spruce budworm
600
600
400
400
200
200
00
0000
2200
9900
1199
8800
1199
7700
1199
6600
1199
5500
1199
4400
1199
3300
1199
2200
1199
1100
1199
0000
2200
9900
1199
8800
1199
7700
1199
6600
1199
5500
1199
4400
1199
3300
1199
2200
1199
1100
1199
Year
Source: CFS, Forest Insect and Disease Survey
Western balsam bark beetle
0000
2200
9900
1199
8800
1199
7700
1199
6600
1199
5500
1199
4400
1199
3300
1199
2200
1199
1100
1199
8000
8000
Mapped outbreak area (ha × 1033)
Area affected by eruptive herbivores in western Canada
Year
Caution!
Most short-term, local changes in forest pest dynamics
are due to land-use changes, other disturbances and/or
natural fluctuations in distribution and abundance,
. . . not necessarily climate change
. . . an example
Affected by mountain pine beetle
Ù Increasing outbreak severity/impact?
Susceptible pine
Ù Increasing susceptible hosts
• Selective harvesting
• Fire suppression
8
Area of pine burned (ha × 1033)
Area (ha × 106) in BC
10
6
4
2
0
1900
1920
1940
1960
1980
2000
Year
Adapted from Taylor and Carroll 2004
400
300
200
100
0
1930
1950
1970
Year
1990
Question:
How will changing climate affect forest insect
disturbance?
Bounding the question…
Predicted change in annual mean temp
2041-2060 versus 1971-1990
a) Regional focus - western North America
• Predicted climate change impacts become
increasingly heterogeneous at broader
spatial scales.
b) Future window ≤50 years – host range ≈static
°C
4.0
3.5
3.0
2.5
2.0
1.5
• A tree species established on a site will
persist there long after suitable conditions
for establishment have disappeared
(Payette 1993).
• Does not preclude climate-induced host
stress.
Canadian Centre for Climate Modelling & Analysis,
CRCM3.6.1 following IPCC IS92a scenario
A general framework
The spatio-temporal ubiquity of a potential forest insect
disturbance agent will constrain the suite of landscape-level
consequences associated with a changing climate.
Ù Native ubiquitous – insect range ≡ host range
Ù Native innocuous – insect historically benign
Ù Native invasive
– insect range ≠ host range
Ù Exotic invasive
– introduced species
A general framework
The spatio-temporal ubiquity of a potential forest insect
disturbance agent will constrain the suite of landscape-level
consequences associated with a changing climate.
Ù Native ubiquitous – ∆ outbreak frequency/duration,
Ù Native innocuous
Ù Native invasive
Ù Exotic invasive
herbivory rate
– ∆ herbivory rate
– ∆ outbreak frequency/duration,
herbivory rate; range expansion
– ∆ herbivory rate; range expansion
Bark beetles:
Ù
Ù
Ù
Ù
Reproduction requires tree mortality
Trees employ effective defenses – toxic resin
Defensive capacity sensitive to climatic variation (moisture stress)
Evidence for recent impacts of CC on severity/extent of disturbance
Photo: B. Aukema
“Native ubiquitous”
Picea spp.
Ù The spruce beetle
(Dendroctonus rufipennis)
Ù Insect range ≡ host range
Ù Potential CC impacts:
•
•
•
From: Holsten EH, Their RW, Munson AW, Gibson KE. US Forest Service
Forest Insect & Disease Leaflet 127
∆ outbreak frequency
∆ outbreak duration
∆ herbivory rate
Spruce beetle outbreak history
(western Canada)
Annual area (ha × 103 ) of mortality
300
250
200
Ù Large outbreaks in recent decades
Ù Outbreaks during previous centuries?
• tree rings, anecdotal evidence
150
100
Ù Influence of host availability?
• unknown
50
0
1900
1920
1940
1960
Year
1980
2000
Ù Forest management impacts?
• unlikely
The northern outbreak
Ù Alaska and Yukon, ≈2 million ha, 1994-2005
Ù Unusually high levels of mortality
Ù Increased herbivory rate?
Spruce beetle 1994-2005
Source:
Canadian Forest Service
US Forest Service
BC Ministry of Forests and Range
Effects of climate change on spruce beetle dynamics
• Univoltine broods =
Increased risk of beetle
outbreaks or accelerated
rate of spruce mortality in
existing epidemics.
0
1
2
3
4
2000
1990
1980
1970
1960
5
1950
Adults
Adults overwinter
overwinter
• Inc. herbivory rate
-2
-1
1940
Year 1
ae
(Hansen and Bentz 2003)
-3
1930
Pu
p
Aug
A
emdeults
rge
Larvae
Adults
Ma y
s
Egg
J ul
11
1920
Jun
12
1900
Warming
13
hot, dry
Adults
Adults overwinter
overwinter
14
cool, moist
Year 2
15
1910
A
em dul
er ts
ge
Larvae
Larvae overwinter
overwinter
Pup
ae
Aug
g
Au
Year 1
e
va
r
La
J ul
lt s
Adu
La
rv
ae
May
Eggs
Jun
Mean May-Aug temp (°C)
J ul
Jun
Ma y
b) Increased host susceptibility
Normalized precip – temp
a) Altered voltinism
Year
Barber VA, Juday GP, Finney BP. 2000. Nature 405: 668-673
“Native innocuous”
Pinus edulis
Ù The pinyon ips beetle
(Ips confusus)
Ù Historically benign
Ù Potential CC impacts:
• ∆ herbivory rate
Photo: N. Cobb
The pinyon Ips outbreak
(US southwest)
Annual area (ha × 103 ) of mortality
1,400
1,200
Photo: C. Allen
1,000
Ù Population eruption in recent years
Ù Outbreaks during the past?
• 1950’s (associated with drought)
800
600
Ù Influence of host availability?
• possibly
400
200
0
1997 1998 1999 2000 2001 2002 2003
Year
Source: Craig Allen
Ù Forest management impacts?
• unlikely
Pine mortality 2000-2003
Ù Pinyon pine mortality ≈1.4 million ha
Ù Widespread conversion from PJ to J woodlands
Ù Increased herbivory rate?
2000-2003 Mortality
Pinyon pine
Ponderosa pine
US drought monitor
D0 Abnormally dry
D1 Drought - moderate
D2 Drought - severe
D3 Drought - extreme
D4 Drought - exceptional
July 23, 2002
Valid 8am EDT
“Native invasive”
Lodgepole pine
Ponderosa pine
Mountain pine beetle
Jack pine
Lodgepole/jack hybrids
Ù The mountain pine beetle
(Dendroctonus ponderosae)
Ù Insect range ≠ host range
Ù Potential CC impacts:
•
•
•
•
∆ outbreak frequency
∆ outbreak duration
∆ herbivory rate
range expansion
Photo: K. Bolte
Mountain pine beetle outbreak history
(western Canada)
Annual area (ha × 103) of mortality
10,000
Affected by MPB
Susceptible pine
8,000
Ù Largest outbreak in recorded history
6,000
Ù Outbreaks during previous centuries?
• tree rings
4,000
Ù Influence of host availability?
• absolutely
2,000
Ù Forest management impacts?
0
1900
1920
1940
1960
1980
Year
Adapted from Taylor and Carroll 2004
2000
• Likely (selective harvest, fire
suppression)
Mountain pine beetle range expansion?
Ù Infestations occurring
further North, East…
Peace River
Willmore
Jasper
Whitebark Pine
Ù … and at higher elevations
than previously recorded
(see Logan et al. 2001)
-40
BRITISH
COLUMBIA
ALBERTA
MPB – limits
(historical)
Ù Cool summers
Ù Winter minimums
(below -40°C)
Weather stations
A model of climatic suitability
Zone 1
P1: > 305 degree-days above 5.6 ºC from
Aug. 1 to end of growing season, and
> 833 degree-days from Aug. 1 to
Jul. 31 the following year.
Zone 2
Loop over grid points, elevations,
exposures (slopes and aspects)
P2: Minimum winter temps > -40 ºC.
P4: Total precipitation from Apr. to Jun.
below long-term avg.
X1: Index of variability of growing
season precipitation.
X2: Index of aridity
BioSim
P3: Avg. maximum Aug. temps ≥ 18 ºC.
Climatic zones
Select “best” weather stations Elevation difference
Distance
Correct T (lapse rates and exposure)
Run model
Target event = a + ƒ(lat, long, elev, expos) + ε
Climatic suitability = [F(P1…4) • (X1• X2)1/2]
0 = Very low
0.01 – 0.05 = Low
0.06 – 0.15 = Moderate
0.16 – 0.35 = High
≥ 0.36 = Extreme
From: Carroll et al. 2004. Can. For. Serv., Inf. Rep. BC-X-399
Digital elevation model
Target event map
From: Régnière 1996. Environ. Entomol. 25: 869-891
55
10
10
00
00
1199
2211
1199 -5500
3311
1199 -6600
4411
1199 -7700
5511
-1199 8800
6611
1199 -9900
7711
--00
00
1199
2211
1199 -5500
3311
1199 -6600
4
411
1199 -7700
5511
-1199 8800
6611
1199 --9900
7711
--00
00
% Area
Very low
14
14
12
12
10
10
88
66
44
22
00
25
25
Extreme
30
30
25
25
20
20
15
15
10
10
55
00
Low
20
20
15
15
10
10
1199
2211
1199 -5500
3311
1199 -6600
4
411
1199 -7700
5511
-1199 8800
6611
1199 -9900
7711
--00
00
Extreme
1199
2211
1199 -5500
3311
1199 -6600
4411
1199 -7700
5511
-1199 8800
6611
1199 -9900
7711
--00
00
Low
1199
2211
1199 -5500
3311
1199 -6600
4411
1199 -7700
5511
-1199 8800
6611
1199 -9900
7711
--00
00
High
% Area
Moderate
% Area
Climatic suitability
% Area in climatic suitability class
30
30
25
25
20
20
15
15
10
10
55
00
40
40
High
Moderate
Very low
30
30
20
20
From: Carroll et al. 2004. Can. For. Serv., Inf. Rep. BC-X-399
1941 - 1970
Climate change-induced
range expansion
Climatic suitability
Very low
Low
Moderate
High
Extreme
1400
Historic suitability = “Very Low”
1200
1000
800
600
400
No. infestations
1970
1971
200
0
1950
2500
1960
1970
1980
1990
2000
Historic suitability = “Low”
2000
1500
1000
500
1941 - 1970
0
1950
1960
1970
1980
1990
2000
From: Carroll et al. 2004. Can. For. Serv., Inf. Rep. BC-X-399
Potential for boreal invasion
Ù Climate change = increased
suitable habitat for MPB
Ù Increased habitat = rapid
expansion by MPB
Ù Breach of Rocky Mountain geoclimatic barrier
Ù Additional warming = continued
range expansion North/East?
Climate change induced-range expansion: invasion of the boreal forest?
Lodgepole pine
Ponderosa pine
Mountain pine beetle
Jack pine
Lodgepole/jack hybrids
Ù Lodgepole/jack pine
hybrid zone
Ù Immediately adjacent
newly established pop’n
Ù Invasion corridor?
MPB climatic
suitability
1981 - 2010
1981-2010
Very low
Low
Moderate
High
Extreme
Adapted from: Carroll et al. 2004. Can. For. Serv., Inf. Rep. BC-X-399
MPB climatic
suitability
1991 - 2020
1991-2020
Very low
Low
Moderate
High
Extreme
Adapted from: Carroll et al. 2004. Can. For. Serv., Inf. Rep. BC-X-399
MPB climatic
suitability
2001
- 2030
2001-2030
Very low
Low
Moderate
High
Extreme
Adapted from: Carroll et al. 2004. Can. For. Serv., Inf. Rep. BC-X-399
MPB climatic
suitability
2011 - 2040
2011-2040
Very low
Low
Moderate
High
Extreme
Adapted from: Carroll et al. 2004. Can. For. Serv., Inf. Rep. BC-X-399
MPB climatic
suitability
2021
- 2050
2021-2050
Very low
Low
Moderate
High
Extreme
Adapted from: Carroll et al. 2004. Can. For. Serv., Inf. Rep. BC-X-399
MPB climatic
suitability
2031
- 2060
2031-2060
Very low
Low
Moderate
High
Extreme
Adapted from: Carroll et al. 2004. Can. For. Serv., Inf. Rep. BC-X-399
Range expansion 2006 update
Jack pine
Lodgepole /Jack pine hybrids
Lodgepole pine
Ponderosa pine
Mountain pine beetle infestations (2005)
Confirmed infestation locations (2006)
Ù MPB established in
hybrid zone
Grand Prairie
Jasper
National
Park
Edmonton
Red Deer
Banff
National
Park
Calgary
Sources: BC Ministry of Forests, Alberta Sustainable Resources Development
Ù If CC scenario
true, and MPB
dynamics in jack
pine similar to
lodgepole, then
cont’d eastward
expansion probable
Conclusions
Ù Insects are major forest disturbance agents highly sensitive to
climatic variations.
Ù Significant changes to climatic conditions relevant to herbivorous
forest insects have already occurred in western North America.
Ù Impacts of climate change are difficult to distinguish from
natural variability and effects of forest management
Ù
Ù
Ù
Within the next 50 years:
The spatio-temporal ubiquity of an insect disturbance agent will
determine the suite of potential landscape-level consequences of
climate change.
Native ubiquitous & native innocuous pests = altered outbreak
characteristics, esp. herbivory rates
Native invasives (and exotics) = range expansion