Magnani Federico, Mencuccini Maurizio, Borghetti Marco, Berbigier Paul, Berninger Frank, Delzon Sylvain, Grelle Achim, Hari Pertti, Jarvis Paul G, Kolari Pasi, Kowalski Andrew S, Lankreijer Harry, Law Beverly E, Lindroth Anders, Loustau Denis, Manca Giovanni, Moncrieff John B, Rayment Mark, Tedeschi Vanessa, Valentini Riccardo, Grace John
Department of Fruit Tree and Woody Plant Science, University of Bologna, Bologna I-40127, Italy.
Nature. 2007 Jun 14;447(7146):848-50. doi: 10.1038/nature05847.
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). 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. The relevance of this measurement effort has also been questioned, 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. 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 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).
北半球的温带和寒温带森林面积约为2×10⁷平方公里，是一个重要的碳汇（每年吸收0.6 - 0.7拍克碳）。尽管农业废弃后森林扩张无疑是这一碳汇活动的重要组成部分，但尽管有广泛的测量站网络，大气二氧化碳增加、气温升高、管理方式变化和氮沉降对成熟森林碳平衡的额外影响仍难以厘清。这种测量工作的相关性也受到质疑，因为定点测量没有考虑到自然（火灾、病虫害、风暴）或人为（森林采伐）干扰的作用。在这里，我们表明，林分更替干扰后的时间动态确实在森林碳固存的总体变异性中占了很大一部分。然而，在排除干扰的混杂影响后，发现森林净碳固存主要受氮沉降驱动，这在很大程度上是人为活动的结果。在现有数据集涵盖的氮沉降范围内，这种影响始终是积极的，这让人怀疑在自然条件下广泛的生态系统氮饱和风险。结果表明，人类最终在直接（通过森林管理）或间接（通过氮沉降）控制着温带和寒温带森林的碳平衡。
