Forests: Current Research

Forest Ecosystems, Disturbance and Climatic Change in Washington State



We addressed the role of climate in four forest ecosystem processes and project the effects of future climatic change on these processes. First, we analyzed how climate affects Douglas-fir growth across the region to understand potential changes in future growth. In areas where Douglas-fir is not water-limited, future growth will continue to vary with interannual climate variability, but in places where Douglas-fir is water-limited, growth is likely to decline due to projected increase in summer potential evapotranspiration.

Second, we used existing analyses of climatic controls on future potential tree species ranges to highlight areas where species turnover may be greatest. By the mid 21st century, some areas of the interior Columbia Basin and eastern Cascades are likely to have climates poorly suited to pine species that are susceptible to mountain pine beetle, and if these pines are climatically stressed, they may be more vulnerable to pine beetle attack. Climatic suitability for Douglas-fir is also likely to change, with substantial decreases in climatically suitable area in the Puget Trough and the Okanogan Highlands.

Third, we examined the relationships between climate and area burned by fire, and projected future area burned in response to changing climate. Regional area burned is likely to double or even triple by the end of the 2040s, although Washington ecosystems have different sensitivities to climate and thus different responses to climatic change.

Fourth, we evaluated the influence of climatic change on mountain pine beetle (MPB) outbreaks by quantifying both host-tree vulnerability and MPB adaptive seasonality. At higher elevations, host-tree vulnerability is expected to increase at higher elevations, as is the viability of MPB populations, leading to increased incidence of MPB outbreaks. The increased rates of disturbance by fire and mountain pine beetle are likely to be more significant agents of changes in forest structure and composition in the 21st century than species turnover or declines in productivity. This suggests that understanding future disturbance regimes is critical for successful adaptation to climate change.


University of Washington College of Forest Resources, USDA Forest Service Pacific Northwest Research Station, University of Idaho Dept. of Geography

Primary Funding

Washington State Legislature (House Bill 1303)

Selected References

For publications on climate impacts on PNW forest ecosystems, please see CIG Publications.

Littell, J.S., E.E. Oneil, D. McKenzie, J.A. Hicke, J.A. Lutz, R.A. Norheim, and M. McGuire Elsner. 2009. Forest ecosystems, disturbance, and climatic change in Washington State, USA. Chapter 7 in The Washington Climate Change Impacts Assessment: Evaluating Washington's Future in a Changing Climate, Climate Impacts Group, University of Washington, Seattle, Washington.