Joint species distribution models for phytosociological data: implications for climate change impacts in Mediterranean overgrazed environments

My stay at the UMR AMAP aims to assess the influence of the spatial variability of topo-climatic, edaphic and anthropogenic factors on the distribution of the Mamora cork oak forest “understory” species in northwestern Morocco. We use a JSDM to model species cover-abundance from 161 floristic relevés inventoried according to Braun-Blanquet's sigmatist phytosociological method during 1999-2004. We employ Multivariate Ordinal Probit Models, which are a natural extension of the JSDMs traditionally used to model presence/absence data. The flexibility of these models is based on the existence of a latent Gaussian field of dimension J that depends on environmental conditions. The findings show that the spatial heterogeneity in precipitation, temperature, and overgrazing rate differently control the cover-abundance distribution of the Mamora understory species. The estimated influences and residual correlations among species have implications for the effect of droughts and increasing overgrazing on species abundance and composition in the study area.