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.