Shrub canopies preserve climatic niche disparity among recruit species in Mediterranean drylands

Abstract

Plant performance has a climatic optimum, especially during early establishment, and declines when conditions deviate from this optimum. However, shrubs can buffer unfavourable climatic conditions by creating more suitable microclimates beneath their canopies, facilitating the establishment of species with disparate climatic niches. Across 10 Mediterranean shrubland sites, we compared climatic niche disparity and phylogenetic structure of plant recruits under shrub canopies versus open ground, integrating environmental, niche and phylogenetic data to reveal underlying abiotic and evolutionary drivers. We show in 10 Mediterranean shrublands that the climatic niche disparity of recruits established under shrub canopies is significantly greater than that of those in open ground. This pattern was only weakly associated with shrub‐driven microenvironmental heterogeneity, estimated using variability in photosynthetically active radiation as a coarse proxy, suggesting that additional abiotic factors may also contribute to recruit niche disparity. In addition, recruit assemblages beneath shrubs were composed, on average, of more distantly related species. Combined with phylogenetic conservatism in the aridity‐response axis of their climatic niche, this pattern results in the co‐occurrence of recruits with higher disparity in key climatic niche axes beneath canopies. Synthesis . Plant canopies host recruit species that exhibit a wide diversity of climatic niches, which may play a role in maintaining biodiversity under ongoing and future climate change.