干旱是地球上最普遍的自然扰动因子之一。干旱塑造着地球上的植被，决定着森林和草地类型，间接影响大型动物或食草动物/昆虫的分布格局。怎么强调干旱对地球生态系统的影响都不为过。目前，生态学界和植物生理学界对干旱发生的机制和影响进行了大量的研究，成果多如牛毛。但，全球尺度的干旱影响研究做的还不是很彻底。

主要是因为量化的问题，如，该怎么量化植被的分布或活动，哪个指标比较好？如何量化干旱，干旱指标有数十个之多，哪个比较好？这些问题是困扰人们进行相关研究的技术问题。

近期，伍兹霍尔研究中心(Woods Hole Research Center)的Schwalm等人基于全球植被总的第一性生产力（GPP，植被总光合能力）和量化干旱的较好指标SPEI进行了全球尺度植被响应干旱的恢复力评估。作者发现，影响干旱恢复时间首当其冲的因子是温度和降水等气象指标，像生物多样性和二氧化碳的施肥效应则排在其次。有意思的是，作者还发现，从干旱中恢复过来的时间最久的生态系统类型竟然是热带雨林和北方高纬度地区的植被（如冻原或荒漠、不毛之地等）。他们解释道，热带雨林由于很少经历干旱，对干旱的适应能力较弱，因此需要更长时间恢复；而北方稀疏植被由于低温或者降雨较少，帮助恢复的资源不充分，因此恢复能力也有较大削弱，因此也需要更长时间恢复。作者进一步解释，过热、过冷和少雨的地区恢复时间都会较长。

考虑到在本世纪干旱是一种普遍且持久的自然现象，植被恢复的时间，从作者的角度来看，会越来越长，因此，生态系统提供的服务功能会大为削弱。

目前，Schwalm等人的研究论文“Global patterns of drought recovery”已经发表在Nature上。

摘要：

Drought, a recurring phenomenon with major impacts on both human and natural systems^{1, 2, 3}, is the most widespread climatic extreme that negatively affects the land carbon sink^{2, 4}. Although twentieth-century trends in drought regimes are ambiguous^{5, 6, 7}, across many regions more frequent and severe droughts are expected in the twenty-first century^{3, 7, 8, 9}. Recovery time—how long an ecosystem requires to revert to its pre-drought functional state—is a critical metric of drought impact. Yet the factors influencing drought recovery and its spatiotemporal patterns at the global scale are largely unknown. Here we analyse three independent datasets of gross primary productivity and show that, across diverse ecosystems, drought recovery times are strongly associated with climate and carbon cycle dynamics, with biodiversity and CO₂ fertilization as secondary factors. Our analysis also provides two key insights into the spatiotemporal patterns of drought recovery time: first, that recovery is longest in the tropics and high northern latitudes (both vulnerable areas of Earth’s climate system¹⁰) and second, that drought impacts¹¹ (assessed using the area of ecosystems actively recovering and time to recovery) have increased over the twentieth century. If droughts become more frequent, as expected, the time between droughts may become shorter than drought recovery time, leading to permanently damaged ecosystems and widespread degradation of the land carbon sink.