Pre and post fire carbon dynamics in a Florida scrub oak

Background/Question/Methods and Results/Conclusions

Scrub oak is a xeromorphic shrub ecosystem discontinuously distributed in coastal and inland Florida. It supports a high biodiversity which includes a large number of endangered and threatened species.  Its structural features are maintained by a fire return cycle of 7 to 10 years which maintains the biodiversity. Management of fire prone ecosystems such as this raises the question of whether the management strategy contributes to the system being a carbon sink or carbon source over the long-term.  We used eddy covariance and biometric approaches to measure carbon dynamics in a Florida scrub oak ecosystem located at Kennedy Space Center in east Central Florida from April 2004 to December 2007. The study site was controlled burned in February 2006. Two years previous to fire, the site experienced average precipitation but drought conditions during the two years after fire. Net ecosystem production (NEP) was 419 g C m^-2 yr^-1 during the first year of measurements, and the ecosystem incorporated 823 g C m^-2 during the 22 months before the fire. Aboveground net primary production (NPP) represented 50% of annual NEP. Carbon released by fire reached 316 g C m^-2. Ecosystem respiration (Re) dominated the carbon balance during the first six months after fire, and the ecosystem released an extra 119 g C m^-2. However, gross ecosystem production (GEP) increased with leaf area index (LAI) after fire, dominating the carbon balance during the following six months. The ecosystem was a carbon sink of 88 g C m^-2 yr^-1 during the first year after the fire. Leaf area index (LAI) reached 1.54 m² m^-2 by October 2007 (80% of pre-burn value for the same time period).  The scrub oak ecosystem was a continuous carbon sink six months after the fire despite the dominant drought conditions during 2006 – 2007. The ecosystem offset 80% (251 g C m^-2) of the carbon released in the fire during the following twenty two months after the fire. Considering the fire return cycle of 7 to 10 years and the fact that the study site and a similar site nearby incorporated more than 400 g C m^-2 yr^-1 during the two years before fire, this scrub oak is a net carbon sink in the landscape under current management strategies.