Ph.D. Dissertation Abstract by Crystal Raymond (2010)

The purpose of this dissertation is to quantify the influence of forest age and climate-driven changes in fire regimes on carbon (C) storage potential in forests of Washington, U.S. This research can improve climate change mitigation and adaptation strategies by indentify forests that have the greatest potential to store additional C and are at the greatest risk of losing C because of more fire in a warmer climate. In this dissertation, I used inventory data and allometric methods to estimate forest C pools and fluxes and non-linear regression to model C dynamics as a function of forest age at two scales: subregions and forest types. Theoretical successional patterns of live biomass accumulation and net primary productivity (NPP) were more apparent at the scale of forest types than subregions. At both scales, dead biomass was characterized more by variability than by a relationship with stand age. Maximum live biomass varied from 6.5 kg C m-2 to 38.6 kg C m-2 and the age at which 90% of the maximum was reached varied from 57 yrs to 838 yrs. Peak NPP varied from 0.37 kg C m-2 yr-1 to 0.94 kg C m-2 yr-1 and the age at which NPP declined varied from 65 yrs to 543 yrs. I investigated the consequences of climate-driven changes in fire regimes on C pools and fluxes for the 21st century. Forests of the western Cascades are projected to be at greater risk of C losses with 21st century fire regimes. For the 2040s, live biomass is projected to decrease by 24% to 37% and coarse woody debris biomass (CWD) by 15% to 25% in the western Cascades. Losses of live biomass are projected to be lower for eastern Washington (17% - 26%), and CWD biomass is projected to increase. Landscape mean NPP is projected to increase in low-elevation forests of the western Cascades and decrease elsewhere. Wet forests of the western Cascades and Okanogan Highlands are projected to have the greatest increases in consumption of live biomass. Increases in consumption of CWD are high for most forests and are projected to be 4 times greater than increases in consumption of live biomass.