The effect of afforestation on a regional carbon sink: a case study in the Yangtze River Delta, China

As one of the most densely populated and economically developed regions in China, Yangtze River Delta (YRD) has confronted with substantial land cover change (LCC) over the past several decades. This study investigates the impact of climate change and LCC on carbon dynamics in the YRD region for 1990-2019, taking advantage of a high-resolution vegetation model and two well-established LCC data in China. Simulated gross primary productivity increases from 0.52 +/- 0.02 Pg[C] yr-1 in the 1990s to 0.57 +/- 0.01 Pg[C] yr-1 in the 2010s with the major contribution by CO2 fertilization effect. The regional carbon sink, measured as net biospheric productivity (NBP), peaks at 0.03 Pg[C] yr-1 in the 2000s but remains stable or slightly decreases in the 2010s depending on the LCC datasets. Forests act as the main contributors to the enhancement of the regional carbon sink, with negative contributions from the loss of shrubland and grassland. The stable NBP during 2000-2019 suggests a potential slowdown in the efficacy of carbon sink as forests mature. While forest expansion significantly promotes NBP, the carbon released during the replacement of other vegetation types suggests that afforestation efforts need to be complemented with associated supportive measures to prevent newly forested areas from becoming net carbon sources.