Carbon dynamics of China’s forests during 1901–2010: The importance of forest age

Abstract

The forest ecosystem plays a significant role in long-term carbon sequestration. The magnitude of a forest carbon sink is determined by the combination of intrinsic biotic factors (i.e. forest age) and extrinsic environmental driving factors (i.e. temperature, precipitation, nitrogen deposition). The mechanism of how forest age affects the carbon balance is still unclear. Furthermore, forest age is a useful surrogate variable for analyses of the impact of disturbances on forest carbon and an important parameter for assessing carbon mitigation potential of forests at regional scale. Without considering forest age, large uncertainties exist in the simulating forest carbon cycle at regional scale. In this study, we analyzed the effect of forest age information on carbon uptake of China’s forests based on a process-based model (Integrated Terrestrial Ecosystem Carbon budget, InTEC model) in the last century, with integration of two forest age maps at 1 km spatial resolution which were derived from inventory data and remote sensing AVHRR NDVI. Inter-annual variability of net primary productivity in China’s forests during 1901–2010 based on InTEC model coupled with inventory data and remote sensing data was similar with each other. Meanwhile, the comparison approach indicated that the errors of 5 years in forest age might cause uncertainties of 25% in simulated net ecosystem productivity of China’s forests. We also discussed the significance of forest age in ecosystem process-based model and the uncertainties of carbon balance of China’s forest ecosystem during 1901–2010. Besides, the hypothesis assumed that no large-scale deforestation occurred since1950s and mature forests (and older forests) were covered the whole China. We adjusted forest age structure for different forest types and regions to simulate the effect of changes in forest age on distribution of carbon balance in China. The important finding is that the loss of carbon sink in China’s forests induced by disturbances (i.e. deforestation, afforestation or natural disturbances) is about 3.80 Pg C during last century. Based this hypothesis, China’s forests in the last two decade manifested a large carbon sink (0.23 Pg C a - 1). Currently, many process-based models are not capable of reflecting the impact of land disturbances because the explicit forest age information are lacking. Our study incorporated the forest age in models successfully and explored the effect of forest age on the simulating carbon balance of forests. The application of forest age in large-scale carbon modeling can improve the accuracy of simulated carbon dynamics and explore the uncertainties in carbon cycle models.