Consequences of climate change for biogeochemical cycling in forests of northeastern North America

A critical component of assessing the impacts of climate change on forest ecosystems involves understanding as- sociated changes in the biogeochemical cycling of elements. Evidence from research on northeastern North American forests shows that direct effects of climate change will evoke changes in biogeochemical cycling by altering plant physiology, for- est productivity, and soil physical, chemical, and biological processes. Indirect effects, largely mediated by changes in spe- cies composition, length of growing season, and hydrology, will also be important. The case study presented here uses the quantitative biogeochemical model PnET-BGC to test assumptions about the direct and indirect effects of climate change on a northern hardwood forest ecosystem. Modeling results indicate an overall increase in net primary production due to a lon- ger growing season, an increase in NO₃^- leaching due to large increases in net mineralization and nitrification, and slight de- clines in mineral weathering due to a reduction in soil moisture. Future research should focus on uncertainties, including the effects of (1) multiple simultaneous interactions of stressors (e.g., climate change, ozone, acidic deposition); (2) long-term atmospheric CO₂ enrichment on vegetation; (3) changes in forest species composition; (4) extreme climatic events and other disturbances (e.g., ice storms, fire, invasive species); and (5) feedback mechanisms that increase or decrease change.