Adaptive Forest Management and Climate Change

Adaptive Forest Management Practices with Tree Health and Climate Change

Along the corridor from Tiger Mountain over Snoqualmie Pass to the North Fork of the Teanaway River trees are engaged in a process of resisting mortality from drought in the summer, disease, and pest outbreaks. Disturbance events such as lighting strikes, landslides, and fires also cause tree mortality seasonally. Forest managers during the 1990s dealt with these threats to forest health in the warmest decade on record. The health of trees in this area is fundamentally connected to climatic conditions and cycles of regeneration for individual species.

Trees respond individually with climatic variation. Currently, climatic variability affects tree regeneration at decadal scales, influenced by the Pacific Decadal Oscillation (PDO) and the El Nino Southern Oscillation (ENSO). As temperature and precipitation vary, managers can use seasonal climate forcasts to anticipate the conditions for the threats to forest health. Pests, such as the bark beetle, attack Douglas-fir stands in warmer years with greater success because of increased stress on the trees from drought coupled with favorable life cycle temperatures for the beetles.

The key to regeneration are the growth factors such as snowpack depth and duration, the length of growing season, and soil moisture in summer. The effects of a warmer climate on tree regeneration will be site specific in the Northwest depending on precipitation patterns. According to David Peterson, a joint UW/Forest Service Scientist, in high snow forests tree regeneration is likely to increase, in high rain forests regeneration may increase, and in dry forests regeneration is likely to decrease. For instance, at the site on the North Fork of the Teanaway River, many of the different tree species, especially the late successional ones, are likely to undergo stress from drought conditions with less precipitation falling on the eastside of the Pass in a warmer climate whearas at Ashael Curtis, on the western side of the Cascades, the threats to forest health may be more related to forest fire danger due to the moratorium on harvesting trees on Forest Service land.

References
Dale et al., "Climate Change and Forest Disturbances", BioScience, September 2001, Vol. 51 No 9, 723-734.

Aber et al., "Forest Processes and Global Environmental Change: Predicting the Effects of Individual and Multiple Stressors", BioScience, September 2001, Vol. 51, No 9, 735-751.

Peterson, David W. and David L.Peterson, "Mountain Hemlock Growth Responds to Climatic Variability at Annual and Decadal Time Scales", Ecology, 82 (12), 2001, 3330-3345.

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