Gross Primary Production of Global Forest Ecosystems Has Been Overestimated

Abstract:

Coverage rate, a critical variable for gridded forest area, has been neglected by previous studies in estimating the annual gross primary production (GPP) of global forest ecosystems. In this study, based on forest ecosystem carbon budget model for china (FORCCHN), we investigated to what extent the coverage rate could impact forest GPP estimates from 1982 to 2011. Here we show that the traditional calculation without considering the coverage rate globally overestimated the forest gross carbon dioxide uptake by approximately 8.7%, with a value of 5.12±0.23Pg C yr^-1, which is equivalent to 48% of the annual emissions from anthropogenic activities in 2012. Actually, by taking the coverage rate into account, the global annual GPP of forest ecosystems is approximately 53.71±4.83Pg C yr^-1 for the past 30 years with 46.19±4.24Pg C yr^-1 for forest grids and 7.52±1.59Pg C yr^-1 for non-forest grids. Accordingly, we argue that forest annual GPP calculated by previous studies has been overestimated due to the exaggerated forest area, and therefore, coverage rate may be a required factor to further quantify the global carbon cycle.