Increasing Temperatures in Mountainous Regions of
the Western United States and Effects on Insect
Outbreaks
Jeffrey A. Hicke
Natural Resource Ecology Laboratory
Colorado State University
Jesse A. Logan
USDA Forest Service
James Powell
Utah State University
Dennis S. Ojima
Natural Resource Ecology Laboratory
Colorado State University
Interactions among forests and insects, fire, and climate
insect life
cycle
insect
outbreaks
coarse woody
debris
climate
atm. CO2
stand age, density, forest C/N
basal area
stocks/fluxes
fire
Climate change and ecosystems
• Globally, temperatures are increasing…ecosystems are impacted in
many ways
• e.g., changes in plant growth or species distributions
• Mountain ecosystems are particularly vulnerable to climate change
• enhanced warming over lower elevations (Diaz and Bradley,
1997; Giorgi et al., 1997)
• ecosystems can often only migrate upward, leading to possible
extinctions
Role of climate in influencing insect outbreaks
•
Large outbreaks of mountain pine beetle have occurred recently or are
ongoing
• >1.5 million ha in the US (1980s)
• 4 million ha in Canada (currently)
•
Recent studies have implicated increasing temperatures as a major
factor in driving insect outbreaks (Fastie et al. 1995, Logan and Powell
2001, Carroll et al. 2004)
•
Projected increases in temperatures will influence the distribution and
outbreak frequency of insect populations
• consequences range from local scales (bark beetles as invasive
species) to global scales (biogeochemical cycling)
Research Goals
•
Understand how climate influences insect outbreaks
•
Predict changes in outbreak frequency and
distribution given future climate scenarios
•
Assess resulting effects on
• host and beetle species distributions
• ecosystem properties such as carbon cycling
Study Objectives
1. Compute regional temperature trends in
mountainous areas of the western US
2. Assess how decadal temperature variability affects
mountain pine beetle outbreak using model of
climate suitability
Temperature data sets used for regional
study in western US mountains
1. Historical Climate Network (HCN)
stations:
• selected stations that are relatively
free of bias
• long records (often to 1900 or earlier)
• monthly resolution
• limited mountain sites
2. VEMAP gridded data set
• 0.5° spatial, daily temporal resolution
• developed from HCN and other
records
• 1895-1993
• topography accounted for within cell
Strategy: Use VEMAP for potential outbreak modeling;
verify long-term temperature behavior with HCN
Model of potential insect outbreak
1. takes as input
•
beetle life stage developmental rates
•
daily temperatures for a year
2. computes
•
time required to complete each life stage (as determined from the
temperatures)
3. outputs number of life cycles per year
•
1 per year => climatically suitable conditions for outbreak (“adaptive
seasonality”)
4. validated at field sites in Idaho
Northern Forest Products Association
Modeled adaptive seasonality occurred in
mountains of western US
Bailey
ecoprovinces
Focus on three ecoprovinces where
outbreak model performed best
Northern Rockies
Bailey
ecoprovinces
Cascades
Middle Rockies
Potential insect outbreaks for different elevation bands
1. Area of suitable climate conditions is declining in Cascades
2. Suitable climate conditions are migrating upslope in Rockies
lower elevations
higher elevations
area
declining
climate
suitability
migrating
up in
elevation
Notes
1.
Adaptive seasonality is only one condition necessary for outbreaks to
occur; also need to consider
• presence of host species
• stand characteristics
2.
MPB populations vary in their developmental rates
• more southern populations (not shown here) are
adapted to warmer temperatures
no net
loss of
outbreak
area?
3.
Other bark beetles currently present at the southern
extent of MPB may migrate north as climate warms
4.
Shift in climatic suitability to higher elevations may impact other pine
ecosystems not adapted to repeated MPB outbreaks
Conclusions
• Temperatures in three mountainous regions in western US:
• were warm in 1930-1940 and currently are increasing
• [regional climate web site: www.nrel.colostate.edu/~jhicke/climate_data]
• Modeled climate suitability for mountain pine beetle outbreak:
• area declined as temperatures increased in the Cascades
• migrated to higher elevations as temperatures increased in the Rockies
• Improved understanding of the role of climate in driving insect outbreaks will
enhance our ability to forecast future forest responses to projected climate
change
Acknowledgements: Lee Casuto; funding provided by USDA, USGS, NASA.