Influence of afforestation, reforestation, forest logging, climate change, CO_2 concentration rise, fire, and insects on the carbon sequestration capacity of the forest ecosystem
Controlling the rising levels of atmospheric greenhouse gas (GHG,especially CO_2) concentration to mitigate global climate change is arguably the most challenging environmental issue encountered by China and many other countries. Forest ecosystem,which is an integral part of terrestrial ecosystems, can play a significant role in absorbing CO_2 from the atmosphere and aiding global climate change mitigation, subsequently contributing to meet the national commitment and demand of carbon emission reduction and carbon sink enhancement. Afforestation and reforestation, as recognized in the Kyoto Protocol, provide relatively low-cost and effective solutions to enhance forest ecosystem carbon sink. Meanwhile, the carbon sequestration capacity of a forest ecosystem is enormously affected by various natural and anthropogenic factors, which may convert the forest ecosystem from a carbon sink to a source. Therefore, the understanding of the influence of afforestation,reforestation,and those factors on the carbon sequestration capacity of the forest ecosystem is important for the accurate estimation of global and regional forest ecosystem carbon budget. In this study, the recent research progresses on the effect of afforestation and reforestation on carbon sequestration capacity of global and regional forest has been reviewed, along with the influence of several natural and anthropogenic disturbances (i.e., forest logging, climate change, CO_2 concentration enhancement,fire,and insect). It was indicated that the carbon sequestration capacity of global afforestation and reforestation was in the range of 148 to 2400 TgC/a, varying regionally as follows: tropical forest (1700 TgC/a) > boreal forest (700 TgC/a) > temperate forest (27500 TgC/a) ? Furthermore,besides climate change and CO_2 concentration rise, other factors that caused carbon emissions in the forest have been summed up and listed below. Forest logging caused the highest carbon emissions (900 TgC/a),followed by forest fire (300 TgC/a), and insects caused the lowest carbon emissions (2-107 TgC/a). Henceforth, more attention should be paid on the influence of carbon sequestration measures and integrated effects of multiple forms of disturbance on the carbon sequestration capacity of forest ecosystems,especially carbon sequestration capacity of forest soil. Furthermore,controlling forest logging and fire,along with reducing or avoiding additional carbon leakage due to afforestation and reforestation would also greatly contribute to forest carbon sequestration.