The human footprint in the carbon cycle of temperate and boreal forests
The human footprint in the carbon cycle of temperate and boreal forests
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DOI：
10.1038/nature05847
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发表时间：
2007-06-14
期刊：
影响因子：
64.8
通讯作者：
Grace, John
中科院分区：
文献类型：
--
作者：
Magnani, Federico;Mencuccini, Maurizio;Grace, John
北方半球的温带和北方森林面积约为2 x 10（7）平方公里，是一个巨大的碳汇（每年0.6 - 0.7千万亿克碳）（1）。虽然农业废弃后的森林扩张肯定是造成这种碳汇活动的重要原因，但尽管有广泛的测量站网络，但大气二氧化碳增加、气温升高、管理做法的变化和氮沉降对已建森林碳平衡的额外影响仍难以理清（2、3）。这种测量工作的相关性也受到质疑（4），因为现场测量没有考虑到干扰的作用，无论是自然的（火灾，害虫，风暴）还是人为的（森林采伐）。在这里，我们表明，时间动态的替代干扰后，确实占了很大一部分的森林碳汇的整体变化。然而，在排除干扰的混杂影响后，发现森林净碳固存绝大多数是由氮沉积驱动的，主要是人为活动的结果（5）。在目前可用的数据集所涵盖的氮沉降范围内，这种影响总是积极的，这使人们对自然条件下广泛生态系统氮饱和的风险产生了怀疑。结果表明，人类最终控制着温带和北方森林的碳平衡，无论是直接（通过森林管理）还是间接（通过氮沉积）。
Temperate and boreal forests in the Northern Hemisphere cover an area of about 2 x 10(7) square kilometres and act as a substantial carbon sink (0.6 - 0.7 petagrams of carbon per year)(1). Although forest expansion following agricultural abandonment is certainly responsible for an important fraction of this carbon sink activity, the additional effects on the carbon balance of established forests of increased atmospheric carbon dioxide, increasing temperatures, changes in management practices and nitrogen deposition are difficult to disentangle, despite an extensive network of measurement stations(2,3). The relevance of this measurement effort has also been questioned(4), because spot measurements fail to take into account the role of disturbances, either natural ( fire, pests, windstorms) or anthropogenic ( forest harvesting). Here we show that the temporal dynamics following stand-replacing disturbances do indeed account for a very large fraction of the overall variability in forest carbon sequestration. After the confounding effects of disturbance have been factored out, however, forest net carbon sequestration is found to be overwhelmingly driven by nitrogen deposition, largely the result of anthropogenic activities(5). The effect is always positive over the range of nitrogen deposition covered by currently available data sets, casting doubts on the risk of widespread ecosystem nitrogen saturation(6) under natural conditions. The results demonstrate that mankind is ultimately controlling the carbon balance of temperate and boreal forests, either directly ( through forest management) or indirectly ( through nitrogen deposition).