Potential effects of climate change on stand development in the Pacific Northwest

Long-term climate and stand structure records and projections from a simulation model are used to explore effectsof predicted changes in temperature on forest development in the Pacific Northwest. Few climate trends have occurredduring the past 92 years, although there have been variations in September temperatures. The lack of climate trendsmakes it impossible to relate past changes in stand development to climate. Measures of stand development from sixlong-term forest plots over the past 7 decades are typical of Douglas-fir stands: stem density declines, leaf area stabilizes,aboveground biomass increases, and shifts in size distribution occur. These changes are consistent with patterns ofnatural succession. A computer model projected forest development under two climate scenarios: current temperatureconditions and temperature warming (such as that predicted under a doubling of atmospheric CO2). The modelpredicted changes in species composition, leaf area, and stem density in response to temperature increases. Totalaboveground biomass is not sensitive to the simulated temperature alterations. Predicted biomass stability suggeststhat the Pacific Northwest forest would continue to store large amounts of carbon in the living trees even with climaticwarming. Therefore, the predicted temperature change would not alter the role of the Pacific Northwest forests asa major storage location of terrestrial carbon. Changes in precipitation patterns or in disturbance frequency or intensitythat might occur with climatic warming could alter these predictions.