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.