Comprehensive description of the carbon cycle of an ancient temperate broadleaved woodland

Abstract

There exist very few comprehensive descriptions of the productivity and carbon cycling of forest ecosystems. Here we present a description of the components of annual Net Primary Productivity (NPP), Gross Primary Productivity (GPP), autotrophic and heterotrophic respiration, and ecosystem respiration (RECO) for a temperate mixed deciduous woodland at Wytham Woods in southern Britain, calculated using "bottom-up" biometric and chamber measurements (leaf and wood production and soil and stem respiration). These are compared with estimates of these parameters from eddy-covariance measurements made at the same site. NPP was estimated as 7.0±0.8 Mg C ha-1 yr-1, and GPP as 20.3+1.0 Mg C ha-1 yr-1, a value which closely matched to eddy covariance-derived GPP value of 21.1 Mg C ha-1 yr-1. Annual RECO was calculated as 18.9±1.7 Mg C ha-1 yr-1, close to the eddy covariance value of 19.8 Mg C ha-1 yr-1; the seasonal cycle of biometric and eddy covariance RECO estimates also closely matched. The consistency between eddy covariance and biometric measurements substantially strengthens the confidence we attach to each as alternative indicators of site carbon dynamics, and permits an integrated perspective of the ecosystem carbon cycle. 37% of NPP was allocated below ground, and the ecosystem carbon use efficiency (CUE, Combining double low line NPP/GPP) calculated to be 0.35&0.05, lower than reported for many temperate broadleaved sites.