Spatial variations and mechanisms for the stability of terrestrial carbon sink in China

Understanding the stability of terrestrial carbon sinks(S-TCS)contributes to more accurate prediction of the terrestrial carbon sink(TCS)in the context of future global change and helps inform climate change mitigation policies.Here,focusing on China,we analyzed the spatial distribution and driving mechanisms for the S-TCS,quantified by the interannual variability of the TCS,using three independent approaches(atmospheric inversions,ecosystem carbon cycle models,and machine learning models based on flux tower observations).We found that the interannual variability of the TCS in China is relatively small compared with the conterminous United States and geographic Europe,indicating a generally stable TCS in China.Spatially,the S-TCS is lower in the North China Plain,Northeast China Plain,and western Yunnan-Guizhou Plateau than in other regions,with varying underlying mechanisms.Large interannual variations in precipitation and high TCS sensitivities to precipitation fluctuations explain the low S-TCS in the North China Plain and Northeast China Plain,while high TCS sensitivities to temperature variations drive the low S-TCS in the western Yunnan-Guizhou Plateau.Our findings highlight the importance of considering local contexts for stabilizing and enhancing China’s TCS in a changing environment.

The role of net ecosystem productivity and of inventories in climate change research:the need for “net ecosystem productivity with harvest”,NEPH

Background:There is an urgent need for quantifying the terrestrial carbon sink in the context of global carbon emissions.However,neither the flux measurements,nor the national wood balances fulfil this purpose.In this discussion article we point at various shortcomings and necessary improvements of these approaches in order to achieve a true quantification of the carbon exchange of land surfaces.Results:We discuss the necessity of incorporating all lateral fluxes,but mainly the export of biomass by harvest,into the flux balance and to recognize feedbacks between management and fluxes to make flux measurements compatible with inventories.At the same time,we discuss the necessity that national reports of wood use need to fully recognize the use of wood for energy use.Both approaches of establishing an ecosystem carbon balance,fluxes and inventories,have shortcomings.Conclusions:Including harvest and feedbacks by management appears to be the main requirement for the flux approach.A better quantification of wood use for bioenergy seems a real need for integrating the national wood balances into the global carbon cycle.

Perspectives on the role of terrestrial ecosystems in the ‘carbon neutrality' strategy

The Chinese government has made a strategic decision to reach ‘carbon neutrality' before 2060. China's terrestrial ecosystem carbon sink is currently offsetting 7–15% of national anthropogenic emissions and has received widespread attention regarding its role in the ‘carbon neutrality' strategy. We provide perspectives on this question by inferring from the fundamental principles of terrestrial ecosystem carbon cycles. We first elucidate the basic ecological theory that, over the long-term succession of ecosystem without regenerative disturbances, the carbon sink of a given ecosystem will inevitably approach zero as the ecosystem reaches its equilibrium state or climax. In this sense, we argue that the currently observed global terrestrial carbon sink largely emerges from the processes of carbon uptake and release of ecosystem responding to environmental changes and, as such, the carbon sink is never an intrinsic ecosystem function. We further elaborate on the long-term effects of atmospheric CO_(2) changes and afforestation on China's terrestrial carbon sink: the enhancement of the terrestrial carbon sink by the CO_(2) fertilization effect will diminish as the growth of the atmospheric CO_(2) slows down, or completely stops, depending on international efforts to combat climate change, and carbon sinks induced by ecological engineering, such as afforestation, will also decline as forest ecosystems become mature and reach their late-successional stage. We conclude that terrestrial ecosystems have nonetheless an important role to play to gain time for industrial emission reduction during the implementation of the ‘carbon neutrality' strategy. In addition, science-based ecological engineering measures including afforestation and forest management could be used to elongate the time of ecosystem carbon sink service. We propose that the terrestrial carbon sink pathway should be optimized, by addressing the questions of ‘when' and ‘where' to plan afforestation projects, in order to effectively strengthen the terrestrial ecosystem carbon sink and maximize its contribution to the realization of the ‘carbon neutrality' strategy.