Future carbon balance of China's forests under climate change and increasing CO2
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abstract
The possible response of the carbon (C) balance of China's forests to an increase in atmospheric CO(2) concentration and climate change was investigated through a series of simulations using the Integrated Terrestrial Ecosystem Carbon (InTEC) model, which explicitly represents the effects of climate, CO(2) concentration, and nitrogen deposition on future C sequestration by forests. Two climate change scenarios (CGCM2-A2 and -B2) were used to drive the model. Simulations showed that China's forests were a C sink in the 1990 s, averaging 189 Tg C yr(-1) (about 13% of the global total). This sink peaks around 2020 and then gradually declines to 33.5 Tg C yr(-1) during 2091-2100 without climate and CO(2) changes. Effects of pure climate change of CGCM2-A2 and -B2 without allowing CO(2) effects on C assimilation in plants might reduce the average net primary productivity (NPP) of China's forests by 29% and 18% during 2091-2100, respectively. Total soil C stocks might decrease by 16% and 11% during this period. China's forests might broadly act as C sources during 2091-2100, with values of about 50 g Cm(-2)yr(-1) under the moderate warming of CGCM2-B2 and 50-200 g Cm(-2)yr(-1) under the warmer scenario of CGCM2-A2. An increase in CO(2) might broadly increase future C sequestration of China's forests. However, this CO(2) fertilization effect might decline with time. The CO(2) fertilization effects on NPP by the end of this century are 349.6 and 241.7 Tg C yr(-1) under CGCM2-A2 and -B2 increase scenarios, respectively. These effects increase by 199.1 and 126.6 Tg C yr(-1) in the first 50 years, and thereafter, by 150.5 and 115.1 Tg C yr(-1) in the second 50 years under CGCM2-A2 and -B2 increase scenarios, respectively. Under a CO(2) increase without climate change, the majority of China's forests would be C sinks during 2091-2100, ranging from 0 to 100 g Cm(-2)yr(-1). The positive effect of CO(2) fertilization on NPP and net ecosystem productivity would be exceeded by the negative effect of climate change after 2050. Under the CGCM2-A2 climate scenario and with direct CO(2) effects, China's forests may be a small C source of 7.6 Tg C yr(-1) during 2091-2100. Most forests act as C sources of 0-40 g Cm(-2)yr(-1). Under the CGCM2-B2 climate scenario and with direct CO(2) effects, China's forests might be a small C sink of 10.5 Tg C yr(-1) during 2091-2100, with C sequestration of most forests ranging from 0 to 40 g Cm(-2)yr(-1). Stand age structure plays a more dominant role in determining future C sequestration than CO(2) and climate change. The prediction of future C sequestration of China's forests is very sensitive to the Q(10) value used to estimate maintenance respiration and to soil water availability and less sensitive to N deposition scenario. The results are not yet comprehensive, as no forest disturbance data were available or predicted after 2001. However, the results indicate a range of possible responses of the C balance of China's forests to various scenarios of increase in CO(2) and climate change. These results could be useful for assessing measures to mitigate climate change through reforestation.
