Will the CO2 fertilization effect in forests be offset by reduced tree longevity?
Will the CO2 fertilization effect in forests be offset by reduced tree longevity?
复制标题
DOI：
10.1007/s00442-010-1837-4
复制
发表时间：
2011-02-01
期刊：
影响因子：
2.7
通讯作者：
Bigler, Christof
中科院分区：
文献类型：
--
作者：
Bugmann, Harald;Bigler, Christof
实验研究表明，在温室大气中，树木生长受到刺激，导致更快的碳积累（即更快的空隙填充率）。然而，更高的生长可能伴随着更短的寿命，从而导致更快的碳释放（即更高的间隙产生率）。这两种抵消过程的净效应尚不清楚。我们使用数据集和建模的新组合来量化这种对地上碳储量的净影响。利用141种温带树种的最大生长率和最大寿命数据，推导了生长刺激与寿命变化之间的关系。我们利用这一关系来修改森林演替模型中树种的各自参数值，并在从寒冷到干燥的树线气候梯度的多个地点研究生长刺激x减少最大寿命的地上生物量的因子设计。结果表明：(1)树木水平上的任何生长刺激都会导致林分生物量的负反馈效应，即使在没有减少林分寿命的情况下；(2)树木寿命的减少倾向于抵消与生长相关的生物量增加；在大多数多物种和单物种模拟中，最可能减少寿命的净效应非常接近于零；(3)当对所有站点的响应进行平均以模拟“景观级”响应时，净效应接近于零。因此，如果希望避免在生态系统水平上的错误推断，就必须考虑森林树木的生态生理反应及其与人口统计过程的联系。我们的结论是，任何二氧化碳施肥效应都很可能被森林树木寿命的相关减少所抵消，从而大大降低了温带森林的碳减缓潜力。
Experimental studies suggest that tree growth is stimulated in a greenhouse atmosphere, leading to faster carbon accumulation (i.e., a higher rate of gap filling). However, higher growth may be coupled with reduced longevity, thus leading to faster carbon release (i.e., a higher rate of gap creation). The net effect of these two counteracting processes is not known. We quantify this net effect on aboveground carbon stocks using a novel combination of data sets and modeling. Data on maximum growth rate and maximum longevity of 141 temperate tree species are used to derive a relationship between growth stimulation and changes in longevity. We employ this relationship to modify the respective parameter values of tree species in a forest succession model and study aboveground biomass in a factorial design of growth stimulation x reduced maximum longevity at multiple sites along a climate gradient from the cold to the dry treeline. The results show that (1) any growth stimulation at the tree level leads to a disproportionately small increase of stand biomass due to negative feedback effects, even in the absence of reduced longevity; (2) a reduction of tree longevity tends to offset the growth-related biomass increase; at the most likely value of reduced longevity, the net effect is very close to zero in most multi- and single-species simulations; and (3) when averaging the response across all sites to mimic a "landscape-level" response, the net effect is close to zero. Thus, it is important to consider ecophysiological responses with their linkage to demographic processes in forest trees if one wishes to avoid erroneous inference at the ecosystem level. We conclude that any CO2 fertilization effect is quite likely to be offset by an associated reduction in the longevity of forest trees, thus strongly reducing the carbon mitigation potential of temperate forests.