Wednesday, August 8, 2007
Exhibit Halls 1 and 2, San Jose McEnery Convention Center
Kristen L. Manies, U.S. Geological Survey, Menlo Park, CA, Jennifer W. Harden, United States Geological Survey, Menlo Park, CA, Michelle C. Mack, Department of Biology, University of Florida, Gainesville, FL, Ben P. Bond-Lamberty, Joint Global Change Research Institute, Katherine P. O'Neill, Environmental Studies, Roanoke College, Salem, VA, Jason C. Neff, Environmental Studies Program and Geosciences Department, University of Colorado, Boulder, CO and Merritt R. Turetsky, Department of Integrative Biology, University of Guelph, Guelph, ON, Canada
Climate change in the boreal forest biome is having a large impact on two of the main controllers of C and N cycling within this region: permafrost and fire. Permafrost, and its effects on soil drainage, controls the inputs and losses of C and N via net primary productivity (NPP), decomposition, and combustion by wildfire. As part of BOREAS and a subsequent experiment called FIRES-ExB, we measured C and N stocks in organic soils and woody debris within different soil drainage types as well as used long-term modeling to examine the balance between soil C and N inputs (NPP as well as fire-killed woody debris) and losses (mainly decomposition and combustion) in context of permafrost or soil drainage class. Soil C and N stocks increased as soil drainage became more poorly drained, largely owing to reduced combustion losses in those systems as well as seasonally colder soil conditions that hamper decomposition in deep soil layers. As a result, soil C dynamics are best captured by modeling soil depth and its variation over fire cycles. Our modeling exercises resulted in three major findings. First, the existence of permafrost has contributed significantly to the amount of C and N stocks within the boreal forest today. Second, fire-killed woody debris accounts for 10 to 60% of the C that persists in deeper soil layers. Lastly, N combustion by wildfire in boreal ecosystems has resulted in long-term losses that exceed the amount of N stored in the soil today by 2-3 times. Our results suggest that climate change effects on boreal soils cannot be understood without explicitly measuring and modeling 1) different organic soil layers, and 2) permafrost and its effects on soil drainage and fire combustion, all of which are underlying controls of C and N storage at the landscape scale.
