Carbon cycling at the landscape scale: the effect of changes in climate and fire frequency on age distribution, stand structure, and net ecosystem production.

Understanding the interactions between climate, fire and forest characteristics-- and how carbon dynamics are affected by these factors--remains an important challenge in ecology. As the size and severity of fires in the western US continues to increase (Westerling et al. 2006), it has become increasingly important to understand carbon dynamics in response to fire. In this study, we investigated these key interactions in the landscape of Yellowstone National Park (YNP). We asked how initial post-fire heterogeneity in forest structure (especially tree density and stand age) controls carbon dynamics over the full life cycle of individual forest stands, and how climate-mediated changes in the fire regime might potentially alter the behavior of the YNP ecosystem as a net sink or source of carbon in the global carbon cycle. We focused on net ecosystem production (NEP), which is the annual net change in carbon stored in the ecosystem— that is, the difference between net primary production (NPP) and heterotrophic respiration. Our research embraced a landscape perspective by considering how NEP varies with spatial variability in structure and forest development. To address our overarching question, we combined a broad-scale chronosequence study of 77 stands distributed widely across the YNP landscape with simulation modeling that incorporated projected climate change. We also developed new allometric equations to predict biomass of the lodgepole pine trees in this region, since existing equations (developed in other regions) were found to be inadequate. Our research has produced one MS thesis (Arcano 2005), two peer-reviewed journal articles to date (Kashian et al. 2006, Smithwick et al. 2008), one submitted manuscript (Tinker et al. Submitted), two in draft form (Kashian et al. Draft, Smithwick et al. Draft), and six manuscripts are in preparation. In the remainder of this report, we highlight some of the key findings