Limited resilience in hotspots of functional richness: the Mediterranean riparian shrublands

Abstract

Functional diversity indices are increasingly being used to describe plant community assembly processes and ecosystem functioning. However, their relevance for predicting alterations in ecosystem functioning of riparian plant communities is still largely unknown. We investigated the functional patterns of riparian forests along environmental gradients, using biological and environmental data from 189 well-preserved riverine locations in mainland Portugal. We calculated functional diversity indices (e.g. Richness, Redundancy, Divergence) for four riparian forest types, namely the Alder woodlands, Ash woodlands, Tree-heath shrublands and Mediterranean shrublands, using their plant species composition and 25 plant functional traits. We used multiple linear regression to predict the effect of the environment in the functional structure of riparian forests and ultimately evaluate the resilience of the riparian forests to environmental fluctuations. We found that Mediterranean shrublands have a significantly higher Functional Richness and a lower Functional Redundancy in comparison to the other riparian forest types. Both regional and habitat variables were important for predicting the functional diversity of riparian forests, with varying patterns according to forest types. In particular, we found that the redundancy of Mediterranean shrublands is mostly affected by precipitation, suggesting their potential vulnerability to climate change in the study area. Our results suggest the usefulness of functional diversity measures for conservation and monitoring the ecological functioning of riparian forests.