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Title: Carbon, water, and heat flux responses to experimental burning and drought in a tallgrass prarie.

Author
item FISHER, MARC - US Department Of Energy
item TORN, MARGERET - US Department Of Energy
item BILLESBACH, DAVID - University Of Nebraska
item DOYLE, GEOFF - Science Application International Corporation(SAIC)
item Northup, Brian
item BIRAUD, S - US Department Of Energy

Submitted to: American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: 10/21/2010
Publication Date: 11/15/2010
Citation: Fisher, M.L., Torn, M.S., Billesbach, D.P., Doyle, G., Northup, B.K., Biraud, S.C. 2010. Carbon, water, and heat flux responses to experimental burning and drought in a tallgrass prarie.. American Geophysical Union. December 13-17.

Interpretive Summary: Abstract only.

Technical Abstract: Natural fires and prescribed burning represent long-standing and currently prevalent disturbances to biogeochemical cycling in grassland ecosystems. We report eddy covariance ecosystem-atmosphere fluxes and biometric variables measured in paired, burned and unburned plots in two paddocks in the US Southern Great Plains over a two-year period that spanned both above (2005) and below (2006) growing season (March to October) precipitation. Prior to the burn (early March, 2005), burned and unburned paddocks initially contained 520±60 g C/m^2 and 360±40 g C/m^2 in above ground biomass respectively. The fire removed approximately 38% of aboveground biomass and left a layer of partially charred, moist, residual litter. Maximum green biomass during the first post-burn growing season was 450±60 g C/m^2 and 270±40 g C/m^2 in the burned and unburned paddocks, respectively. Cumulative net exchange of CO2 totaled -330±30 and -150±30 g C/m^2 in the burned and unburned fields, respectively. This resulted in the burned paddock approximately recovering the carbon lost to the fire, relative to the unburned paddock. Ecosystem respiration (measured by partitioning the eddy covariance fluxes) was 1850±100 g C/m^2 in both fields, agreeing closely with independent measurements made with soil respiration chambers. Insufficient precipitation during the 2006 growing season generated water stress, reducing maximum green biomass to 210±30 g C/m^2 in the burned and 140±30 g C/m^2 unburned fields, representing roughly a two-fold reduction relative to 2005. Net carbon exchange in 2006 was reduced to 45±20 and 13±20 g C/m^2 for the burned and unburned fields respectively, indicating near-zero net exchange in both fields. Ecosystem respiration was also reduced to 1250±50 and 1130±50 g C/m^2, and was again approximately consistent with chamber measurements. On the basis of this study we conclude that carbon, water, and energy responses to water limitation will likely outweigh those from prescribed fire on seasonal to multi-annual time scales for tallgrass prairie under the normal to dry growing conditions that occur in the Southern Great Plains.