森林土地利用变化及其对碳循环的影响

由于人口剧增，人类活动的影响不断加大，在过去100年全球土地利用／土地覆被发生了巨大的变化。最常见的土地利用变化是由森林转变为农业用地。森林砍伐使森林生态系统地上部生物量大大减少，砍伐后作农业用地，降低了植被生产力，减少了土壤有机质的输入，增强了腐殖质的矿化作用，有机质分解速率增加，有机碳贮量随之降低，从而影响到森林生态系统的碳循环，使大量碳元素释放到大气中，引起温室效应，导致全球变暖。另一个常见的土地利用变化是植树造林和森林恢复，这一过程可以增加森林生态系统的碳储量，从而减缓大气CO2体积分数的上升。

Change in the use of forest land and its impact on the carbon cycling

The land use and land cover of the world has obviously changed since the last century. The reason comes from the sharp growth of human population and his intensive activities and exploitation of land. The most common type of forest land use change is the change in agriculture land. After forest has been demolished, its aboveground biomass is much less than that of the origin forest. The productivity of the vegetation will be reduced and the organic matter returned to the soil will be lessened. Cultivation will de- stroy the physical protection of the soil organic matter, accelerate the mineralization of the humus, increase the decomposition speed of the soil organic matter, and then the soil carbon storage will be decreased. The carbon cycling of the forest ecosystem is affected by large amount of carbon that is released into the atmosphere, which leads to the global warming. Another common type of land use change is afforestation and forest recovering. The carbon storage of forest could be increased and the rising of atmospheric CO2 could be slowed down in this process.