HR: 1340h
AN: B23A-0923    [Abstracts]
TI: Interannual Variation of Carbon Fluxes From a Tropical, a Temperate, and a Boreal Evergreen Forest: the Role of Gap Dynamics and Climate
AU: * Sierra, C A
EM: carlos.sierra@oregonstate.edu
AF: Department of Forest Science, Oregon State University, 321 Richardson Hall, Corvallis, OR 97331,
AU: Loescher, H W
EM: hank.loescher@oregonstate.edu
AF: Department of Forest Science, Oregon State University, 321 Richardson Hall, Corvallis, OR 97331,
AU: Harmon, M E
EM: mark.harmon@oregonstate.edu
AF: Department of Forest Science, Oregon State University, 321 Richardson Hall, Corvallis, OR 97331,
AU: Richardson, A D
EM: andrew.richardson@unh.edu
AF: Complex Systems Research Center, University of New Hampshire, Durham, 03824,
AU: Hollinger, D Y
EM: dhollinger@fs.fed.us
AF: Northeastern Research Station, USDA Forest Service, Durham, 03824,
AB: Interannual variation of carbon fluxes can be attributed to different biotic and abiotic controls that operate at different spatial and temporal scales. The type and frequency of disturbance, forest dynamics, and climate regimes are important sources of variability. Assessing the variability of carbon fluxes from these specific sources can enhance the interpretation of past and current observations. Being able to separate the variability caused by stand dynamics from that induced by climate will also give us the ability to determine if the current observed carbon fluxes are within an expected range or by contrast, other non-tested factors affect the annual variation in the overall carbon flux. We explored possible sources of variation in Net Ecosystem Carbon Balance (NECB) using the simulation model STANDCARB. With this model we identified key processes that introduce variation in annual carbon fluxes. Three contrasting ecosystems were used, a tropical forest, a temperate coniferous forest, and a boreal forest. We found that gap dynamics introduced a key source of variation to annual carbon fluxes, but its relative importance differed among the three ecosystems studied. In the tropical forest, gap dynamics and climate each contributed the same amount of variation to the annual carbon exchange. In the temperate and boreal sites, where many forest processes occur at a longer temporal scale than those at the tropical site, climate controlled more of the annual variation of carbon fluxes. These results suggest that the variability controlled by climate affects the internal rates of carbon exchange differently among sites. Our results also showed that the variation of annual carbon fluxes poses important challenges to determine the status of an ecosystem as source, sink or neutral at longer time scales. We found that for systems in dynamic equilibrium, there is a 5 to 10 % chance of incurring in Type I error when testing the hypothesis of neutrality, i.e., NECB = 0. Conversely, in simulations where climate change negatively affected ecosystem productivity, there was an 80 % chance of committing Type II error, even with 50 sequential years of data.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting