Tree ring evidence for limited direct CO2 fertilization of forests over the 20th century
Tree ring evidence for limited direct CO2 fertilization of forests over the 20th century
复制标题
DOI：
10.1029/2009gb003699
复制
发表时间：
2010-09-30
影响因子：
5.2
通讯作者：
Berg, Aaron A.
中科院分区：
文献类型：
--
作者：
Gedalof, Ze'ev;Berg, Aaron A.
大气中二氧化碳含量上升对森林生产力和水利用效率的影响仍然不确定，但它对未来的碳固存率和森林分布有着重大影响。为了解CO2上升对森林的影响所做的努力主要是基于幼苗生长室研究和相对较少的FACE站点。从这些研究的推论是有限的，其一般持续时间短，人工生长条件下，不自然的二氧化碳浓度的逐步增加，以及复制差。在这里，我们分析了来自国际树木年轮数据库（ITRDB）的全球年度径向树生长记录，以证明增长率的增加不能仅由气候变化来解释，并证明对干旱的敏感性降低。我们发现，全球约有20%的地点表现出增长趋势，这不能归因于气候原因，氮沉降，海拔或纬度，我们将其归因于直接的CO2施肥效应。没有发现物种之间的差异，其可能性表现出增长归因于CO2施肥，虽然花旗松（花旗松）和黄松（黄松），两个最常见的采样物种在ITRDB，表现出CO2施肥信号的频率非常接近其置信上限和下限分别。总的来说，这些结果表明，森林的CO2施肥不会以任何实质性的方式抵消排放或减缓变暖，但确实表明，未来的森林动态可能不同于今天所看到的，这取决于场地条件和个别物种对CO2升高的反应。
The effect that rising atmospheric CO2 levels will have on forest productivity and water use efficiency remains uncertain, yet it has critical implications for future rates of carbon sequestration and forest distributions. Efforts to understand the effect that rising CO2 will have on forests are largely based on growth chamber studies of seedlings, and the relatively small number of FACE sites. Inferences from these studies are limited by their generally short durations, artificial growing conditions, unnatural step-increases in CO2 concentrations, and poor replication. Here we analyze the global record of annual radial tree growth, derived from the International Tree ring Data Bank (ITRDB), for evidence of increasing growth rates that cannot be explained by climatic change alone, and for evidence of decreasing sensitivity to drought. We find that approximately 20 percent of sites globally exhibit increasing trends in growth that cannot be attributed to climatic causes, nitrogen deposition, elevation, or latitude, which we attribute to a direct CO2 fertilization effect. No differences were found between species in their likelihood to exhibit growth increases attributable to CO2 fertilization, although Douglas-fir (Pseudotsuga menziesii) and ponderosa pine (Pinus ponderosa), the two most commonly sampled species in the ITRDB, exhibit a CO2 fertilization signal at frequencies very near their upper and lower confidence limits respectively. Overall these results suggest that CO2 fertilization of forests will not counteract emissions or slow warming in any substantial fashion, but do suggest that future forest dynamics may differ from those seen today depending on site conditions and individual species' responses to elevated CO2.