Simulating Picea schrenkiana forest productivity under climatic changes and atmospheric CO2 increase in Tianshan Mountains, Xinjiang Autonomous Region, China

A process-based model, BIOME-BGC, was used to investigate the response of Picea schrenkiana forest to future climate changes and atmospheric carbon dioxide (CO2) concentration increases in the Tianshan Mountains of northwestern China. The model was validated by comparing simulated net primary productivity (NPP) under current climatic conditions with independent field-measured data. Then the model was used to predict P. schrenkiana forest productivity response to the different climatic and CO2 change scenarios. The results showed that NPP increased moderately (about 18.6%) for all sites when both temperature and precipitation changes were taken into account. The main factor contributing to NPP increase was an increase in precipitation, which tended to alleviate moisture stress for P. schrenkiana forest growth. NPP increase was relatively low (about 2.7%) when the physiological fertilizing effect of the doubled atmospheric CO2 concentration was considered alone, in part because of nitrogen limitation and low temperatures. When both climatic changes and doubling of atmospheric CO2 concentration were taken into account, NPP increased more dramatically (from 26.4% to 37.2%). The results also indicated that the interactive effects of climate and CO2 changes were not a simple additive combination of the individual responses. The results provided support for the view that forest response to climatic change depends on local site conditions.