Are strong fire-vegetation feedbacks needed to explain the spatial distribution of tropical tree cover?
Are strong fire-vegetation feedbacks needed to explain the spatial distribution of tropical tree cover?
复制标题
是否需要强烈的火灾植被反馈来解释热带树木覆盖的空间分布？
DOI：
10.1111/geb.12380
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发表时间：
2015
影响因子：
6.4
通讯作者：
Good P
中科院分区：
文献类型：
--
作者：
Good P
目的热带林木火灾死亡的空间格局部分取决于气候，但林木盖度对火灾的反馈也是重要的。我们重新审视了最近提出的一些证据，这些证据表明树木覆盖对火灾的反馈非常强烈，足以使热带大片地区的稀树草原和森林成为替代的稳定状态。检验了以前报道的两条观测证据：(1)热带乔木比例的三峰统计分布；(2)在雨量相似的热带地区不同位置发现不同的乔木比例盖度这一事实。位置全球热带。方法对于上述点(1)，我们分析了由树木生长和自我竞争的Logistic方程预测的树木比例的统计分布，其死亡率在空间上是不同的。(2)在气候模式中，检验了年平均降雨量和平均净第一性生产力(NPP)之间的关系。结果(1)树木覆盖的三峰分布不一定需要树木覆盖对火灾的反馈。它可能是两个因素的组合造成的：植被动态的非线性和气候驱动的死亡率空间差异(中间的火灾生产力假说)。(2)即使没有树木覆盖对火灾的反馈，热带不同位置的降雨量也可能相同，但净初级生产力存在显著差异。主要结论我们的结果表明，对观测结果(1)和(2)的解释不需要强烈的树木覆盖反馈。然而，强烈的火-植被反馈仍然有可能是主要的解释--我们的结果不排除这一点。我们只是简单地证明了另一种假设的可能性(强烈的气候控制)。在现实中，树木覆盖反馈和气候很可能都起到了作用。要将这两种影响完全分开是一件具有挑战性的事情。需要更多的工作来量化它们各自的影响。我们表明，死亡率与生产力的关系图是理解树木覆盖率空间变化的有用工具。
AimThe spatial pattern of tropical fire‐induced tree mortality is partly determined by climate, but feedbacks of tree cover on fire are also important. We re‐examine some recent observations proposed as evidence for very strong tree‐cover feedbacks on fire, sufficient to allow savanna and forest to be alternative stable states over large areas of the tropics. Two pieces of previously reported observational evidence are examined: (1) the trimodal statistical distribution of tropical tree fraction, and (2) the fact that different tree fractional cover is found at different locations in the tropics with similar rainfall.LocationGlobal tropics.MethodsFor point (1) above we analyse the statistical distribution of tree fraction predicted by the logistic equation of tree growth and self‐competition, with spatially varying mortality rates. For (2), the relationship between mean annual rainfall and mean net primary productivity (NPP) in a climate model is examined.Results(1) A trimodal distribution of tree cover does not necessarily require tree‐cover feedback on fire. It can arise from a combination of two factors: nonlinearities in vegetation dynamics and climate‐driven spatial variation in mortality (the intermediate fire–productivity hypothesis). (2) Different locations in the tropics can have identical rainfall but significantly different NPP, even with no feedback of tree cover on fire.Main conclusionsOur results show that strong tree‐cover feedback on fire is not necessary to explain observations (1) and (2). However, it is still possible that strong fire–vegetation feedback is the primary explanation – our results do not rule this out. We simply demonstrate the possibility of an alternative hypothesis (of strong climate control). In reality, it is likely that both tree‐cover feedback and climate contribute. It is challenging to separate these two effects cleanly. More work is needed to quantify their separate effects. We show that plots of mortality versus productivity are useful tools for understanding spatial variations in tree cover.