Forest biomass-carbon variation affected by the climatic and topographic factors in Pearl River Delta, South China.

Subtropical forests function as important carbon sinks for atmospheric CO2. Nonetheless, there remain uncertainties about the effects of climate and topography on subtropical forest biomass-carbon stocks. A continuous biomass expansion factor (BEF) method was applied to forest inventory data to estimate biomass-carbon storage and carbon sink rate, and their changes along with abiotic and biotic factors in the Pearl River Delta (PRD) of South China. BEF equations were built using a set of field-based data. Biomass-carbon increased from 62.92 to 70.56 Mt along with forest growth and increasing forest area during the latest two periods of the national forest inventory (2004-8 and 2009-13). The PRD's forests continued to be net carbon sinks 0.51 t ha-1 yr-1. The PRD's forests have a high potential as biomass-carbon sinks in the future, because 46.75% of the forests are at the young or middle-aged stage. In addition, principal component analysis indicated that both biomass-carbon density and carbon sink rate were positively correlated with the area percentage of mature and over-mature forests, average annual precipitation and minimum temperature, but they were negatively correlated with average annual maximum temperature. Pearson correlation analysis demonstrated that biomass-carbon density and carbon sink rate affected by average altitude, while they were not related to the slope angle.