A wildfire event influences ecosystem carbon fluxes but not soil respiration in a semi-arid woodland

Abstract

The importance of arid and semi-arid ecosystems for global net carbon uptake has recently been highlighted. More information about the drivers of carbon fluxes in these ecosystems is required to advance our understanding of the contribution of dry ecosystems to the global carbon budget. In this study, eddy covariance flux data was used to calculate net ecosystem productivity (NEP), gross primary productivity (GPP) and ecosystem respiration (Reco) in a semi-arid woodland on sandy soil. In January 2014 a wildfire severely damaged the area around the flux tower, burning trees and spinifex and consuming aboveground bark and leaf litter. The flux tower recorded data for one year before the fire (January–December 2013) and more than one year after the fire (May 2014–July 2015). Soil respiration was measured in-situ monthly after the fire (July 2014–June 2015), in burnt and unburnt areas under Eucalyptus tree canopy and inter-canopy representing 25 and 75% of the area, respectively. Before the fire the ecosystem was a net carbon sink, sequestering 81gCm−2 yr−1 in 2013, but became a carbon source after the fire. Reco and GPP declined by about 35% and 65%, respectively, after the fire. Net carbon uptake resumed 12–15 months after the fire with NEP approaching values similar to those before the fire. Soil respiration was significantly higher under tree canopies (1.5μmol CO2 m−2s−1) than in inter-canopy areas (0.9μmol CO2 m−2s−1). Soil respiration was mainly driven by soil water content and thus magnitude and distribution of precipitation, but was not influenced by the wildfire. Accounting for differences in area, soil respiration from inter-canopy and under canopy contributed 51 and 32% to total ecosystem respiration. It can be concluded that carbon flux in this semi-arid woodland was strongly influenced by precipitation and wildfire, with net carbon uptake of the ecosystem beginning approximately one year after the fire.