Simulating Carbon Dynamics and Species Composition Under Projected Changes in Climate in the Puget Sound, Washington, USA

Abstract:

Changing climate has the potential to directly and indirectly alter forest carbon dynamics and species composition, particularly in temperature or precipitation limited systems. In light-limited systems, species-specific response to changing climate could result in an indirect effect of climate through altered competitive interactions. Joint Base Lewis-McChord, in Washington, contains one of the largest intact forested areas in the Puget Sound. Management priorities include development of late-successional forests and conservation. We sought to quantify how projected changes in climate would affect species diversity and carbon (C) sequestration given management priorities. We used Landis-II to simulate forest dynamics over 100 years using current climate and projected climate under two emission scenarios. Preliminary analyses indicate a decrease in soil C, relative to current climate, beginning mid-century for both emission scenarios. Under the low emission scenario, the decrease is compensated by increased aboveground C, while the high scenario experiences a decline in aboveground C. Total ecosystem C was consistent between baseline and low emission climate throughout the simulation. By late-century, the high scenario had an average decrease of 10 Mg C ha^-1. Douglas-fir (DF) accounts for the largest fraction of aboveground biomass (AGB) in the study area. Interestingly, DF AGB was fairly consistent between climate scenarios through mid-century, but diverged during late-century, with the high scenario having the greatest amount of DF AGB (mean 368 Mg ha^-1) and current climate having the lowest (mean 341 Mg ha^-1). We found the inverse relationship when examining all other species. Given the uncertainty associated with climate projections, future simulations will include a larger suite of climate projections and address the secondary effects of climate change (e.g. increased wildfire, disease or insect outbreaks) that can impact productivity.