Terrestrial ecosystems play an important role in the global carbon (C) cycle and have been found to act as net carbon sinks, offsetting 10–60% of the CO2 emitted through human activities over last decades (Ciais et al., 2014; Le Quéré et al., 2015). As a country with vast territory area and the world’s largest population, China significantly contributes to the global carbon balance in terms of both carbon emission (Boden et al., 2009) and carbon uptake (Piao et al., 2009a). Since 2006, China has become the largest CO2 emitter, accounting for 27% of global emissions (Gregg et al., 2008). Whether China can effectively contribute to the mitigation of global warming depends on the magnitude of net C balance (Shao et al., 2016), highlighting the need to adequately quantify the carbon balance of terrestrial ecosystems C cycle in China.
China’s terrestrial ecosystems have been recognized as a substantial carbon sink in recent decades (Piao et al., 2009a; Tian et al., 2011a, b; Shao et al., 2016). However, there was a remarkable uncertainty on whether the terrestrial ecosystems in China are sinks or sources for atmospheric CO2 because they depend heavily on changing climate and land use as well as atmospheric CO2. Over the past century, the average air temperature in China has increased by 0.5 to 0.8°C (Ding et al., 2006), which is higher than the global average (IPCC, 2013). The timing and intensity of climate change in China tend to be above the global average level (Ding et al., 2007). The changes and feedbacks of East Asia summer monsoon systems (Ding and Chan, 2005) may even accelerate the climatic changes in this region. Furthermore, China has also been experiencing a dramatic land-use change that disturbs terrestrial carbon storage and fluxes and consequently has a particularly long-term impact on the carbon cycle at regional scales (Houghton and Hackler, 2003; Tian et al, 2011a). Chinese terrestrial ecosystems likely play a pronounced role in the global carbon dynamics in a changing climate (Fang et al., 2007; Piao et al., 2009a) and human society, which have drawn much attention from both the public and scientific community. To date, considerable efforts and progress have been made to improve our knowledge about China’s carbon budget and its impact factors. However, due to the complex response and feedback of terrestrial carbon cycle to climate change and the anthropogenic disturbance, large uncertainties still exist in the carbon budget (Shao et al., 2016). The mechanisms and factors that govern the terrestrial carbon cycle are not yet fully accounted for in quantify the regional carbon budget (Piao et al., 2009b). In particular, the relationships between individual controlling factor and the spatial and temporal variabilities of carbon balance in China are still poorly quantified under the condition of concurrent changes and complex interactions of the major factors. Furthermore, to date, most studies have focused on the last several decades of the 20th century because the dramatic changes have been recognized to occur in the corresponding periods. Meanwhile, relatively little attention has been paid to the carbon budget of China’s terrestrial ecosystems at a century scale. The role of ecosystems in carbon cycle during the early 20th century should not be ignored even if the relatively weak variabilities, because quantifying long-term terrestrial carbon dynamics will further help us to comprehensively understand the natural and anthropogenic contribution to global carbon cycle and climate change. Moreover, estimating the magnitudes of carbon fluxes at a century scale is critical for evaluating the ecosystem goods and services and cumulative contribution of regional ecosystems to carbon sequestration (Canadell et al., 2007; Ito, 2011; Li et al., 2016) and providing a scientific basis for international climate change negotiations (Heyward, 2011). The research is therefore of great importance to public as well as to policy makers.
Here we apply an extant process-based biogeochemistry model, the Terrestrial Ecosystem Model (TEM; Zhuang et al 2003, 2010) to quantify the carbon budget for China’s terrestrial ecosystems during 1900–2000. Using the spatially explicit historical dataset, we examine how climate, atmospheric CO2 concentrations and land-use changes have collectively affected terrestrial C dynamics in China. The study also strives to identify the key controls to spatial and temporal patterns of C dynamics in this region.