Consequences of climate change for biogeochemical cycling in forests of northeastern

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. Resume´ : Une composante critique de l'estimation de l'impact des changements climatiques sur les ecosystemes forestiers implique la comprehension des changements associes au cycle biogeochimique des elements. Une recherche conduite dans les forets du nord-est de l'Amerique du Nord montre clairement que les effets directs des changements climatiques entraoˆ- neront des changements dans le cycle biogeochimique en alterant la physiologie des plantes, la productiviteforestiere et les processus impliques dans la physique, la chimie et la biologie des sols. Les effets indirects engendres surtout par des changements dans la composition en especes, la longueur de la saison de croissance et le regime hydrique seront aussi im- portants. Une etude de cas est presentee ici a l'aide du modele quantitatif biogeochimique PnET-BGC pour tester des hy- potheses au sujet des effets directs et indirects des changements climatiques sur un ecosysteme forestier de feuillus nordiques. Les resultats des simulations permettent d'anticiper une augmentation generale de la production primaire nette causee par l'allongement de la saison de croissance, une augmentation du lessivage de NO3 - due ade fortes augmentations