Supplementary material and data from: Climatic disequilibrium modulates canopy service across abiotic stress gradients

Canopy service (CS) is defined as the extent to which established (canopy) plants affect the recruitment of new individuals in the community. This service, when positive, is known as facilitation, and is mainly driven by the modification of the microenvironment that plants induce under their canopies, often by buffering the macroclimate. The importance of canopy service in maintaining diversity may increase in the context of climate change. Climate change may also push species away from their niche optima, increasing their so-called climatic disequilibrium (CD). This process can provoke poorer performance, defoliation, and decay of the canopy species, jeopardizing the canopy service they provide. Therefore, canopy CD is expected to modulate canopy service under current climate conditions. In this study, we test (1) whether canopy species experiencing greater CD will exhibit diminished canopy services, and (2) whether the negative impact of CD on canopy service will be more pronounced under increasing abiotic stress conditions (i.e. aridity and continentality). To address these questions, we used a database of 54 communities, mainly distributed across the Mediterranean basin, which includes a total of 316 canopy species involved in 35,941 recruiting interactions. The CD of the species in a given community resulted in contrasted effects on their canopy service depending on the level of climatic stress. The maximum Canopy service occurs at intermediate aridity levels, following a humped-shaped pattern when considering this single climatic stressor. However, when continentality is also considered, a greater intensity of both stressors together increase a positive canopy service linearly, following the Stress Gradient Hypothesis. Our results indicate that abiotic stressors, combined with CD, modulates the canopy service. Consequently, under future climate change scenarios that may increase stress and CD, canopy service will become crucial for the maintenance of the recruiting community.冠层服务（Canopy Service，CS）被定义为成熟冠层植物对群落中新个体补充过程的影响程度。当该服务产生正向效应时，即被称为促进作用，其主要驱动机制为植物在冠层下诱导形成的微环境改造，通常通过缓冲大气候的极端变化实现。在气候变化背景下，冠层服务对于维持群落多样性的重要性可能会有所提升。气候变化还可能促使物种偏离其生态位最适条件，加剧其所谓的气候失衡（Climatic Disequilibrium，CD）。这一过程会导致冠层物种的生长表现变差、落叶甚至衰退，进而威胁其提供的冠层服务。因此，冠层物种的气候失衡被认为会在当前气候条件下调控冠层服务的强度。本研究旨在验证两个假说：其一，气候失衡程度更高的冠层物种，其冠层服务是否会出现减弱；其二，在非生物胁迫加剧的情境下（即干旱度与大陆度升高），气候失衡对冠层服务的负面影响是否会更为显著。为解答上述问题，我们使用了一套涵盖54个群落的数据库，这些群落主要分布于地中海盆地，共包含316种冠层物种，涉及35941个补充互作事件。研究发现，特定群落中物种的气候失衡对其冠层服务的影响，会随非生物胁迫水平的不同而呈现显著差异。仅考虑干旱度这一单一非生物胁迫因子时，冠层服务会呈现驼峰型分布模式，在中等干旱度水平下达到峰值。然而，当同时考虑大陆度时，两种胁迫因子的强度同时升高会与冠层服务呈线性正相关，这一结果符合胁迫梯度假说（Stress Gradient Hypothesis）。我们的研究结果表明，非生物胁迫与气候失衡共同调控着冠层服务的强度。因此，在未来可能加剧非生物胁迫与气候失衡的气候变化情景下，冠层服务对于群落补充过程的维持将变得至关重要。