Ecosystem Physiology, Faculty of Environment and Natural Resources, University Freiburg, Freiburg, Germany.
Plant Biol (Stuttg). 2022 Dec;24(7):1098-1107. doi: 10.1111/plb.13415. Epub 2022 Mar 21.
Increasing durations and frequencies of droughts under climate change endanger the sustainable functioning of forests worldwide. The admixture of species with complementary resource use may increase the resilience of forests towards drought; however, little is known about modifications of species interactions (i.e. facilitation and competition) by increasing drought severity in mixed forests. In particular, knowledge on the regulation of central ecohydrological processes, such as tree water fluxes, is lacking. Therefore, we conducted a literature review to assess the impact of species interactions on tree resilience (resistance + recovery) under increasing drought severity. The classification of studies into three drought classes suggested that beneficial species interactions, i.e. through improved water relations, were prevalent under mild droughts. However, with increasing drought, negative effects, such as interspecific competition, occurred. These negative interactions were prominent under extreme droughts, where even trees with complementary resource-use strategies competed for water resources. Fewer data are available on recovery of water fluxes. The limited evidence supported the patterns observed for drought resistance, with facilitation and complementarity of species in mixtures enhancing tree recovery after moderate droughts. However, after extreme droughts, competition effects and reduced recovery for some species were observed, which can strongly compromise tree resilience. While we acknowledge the importance of mixed forests for biodiversity, ecosystem services or pest resistance, we caution that beneficial species interactions may shift under extreme droughts. Thus, there is an urgent need to investigate species interaction effects on resilience in more depth to adapt forest trees to increasing drought stress.
在气候变化下，干旱持续时间和频率的增加危及全球森林的可持续功能。具有互补资源利用的物种混合可能会增加森林对干旱的恢复力；然而，关于在混合林中增加干旱严重程度对物种相互作用（即促进和竞争）的影响知之甚少。特别是，关于中央生态水文学过程（例如树木水分通量）的调节的知识还很缺乏。因此，我们进行了文献综述，以评估物种相互作用对树木在干旱加剧下的恢复力（抵抗力+恢复力）的影响。将研究分为三个干旱等级表明，在轻度干旱下，有益的物种相互作用（例如通过改善水分关系）普遍存在。然而，随着干旱的加剧，会出现负相互作用，例如种间竞争。这些负相互作用在极端干旱下更为突出，即使具有互补资源利用策略的树木也会争夺水资源。关于水分通量恢复的数据较少。有限的证据支持了对干旱抵抗力观察到的模式，混合物中物种的促进和互补作用增强了树木在中度干旱后的恢复力。然而，在经历极端干旱后，观察到竞争效应和一些物种的恢复能力下降，这可能会严重影响树木的恢复力。虽然我们承认混交林对于生物多样性、生态系统服务或抗虫害的重要性，但我们警告说，在极端干旱下，有益的物种相互作用可能会发生变化。因此，迫切需要更深入地研究物种相互作用对恢复力的影响，以使森林树木适应不断增加的干旱压力。
