Environmental filters determine the distribution of tree species in a threatened biodiversity hotspot in western Mexico

Abstract

Background: Analyzing interactions between vegetation and environmental factors at regional scales provide information for the understanding of species assemblages.
 Hypotheses: Environmental restrictions at higher elevations produce a decreasing species richness pattern along an elevational gradient and the climatic variables related to temperature and precipitation are the main filters of species distribution.
 Objectives: (1) To identify the different assemblages of tree species occurring in a biodiversity hotspot; (2) to analyze the pattern of tree species richness along an elevational gradient; and (3) to analyze the environmental filters that determine the species distribution.
 Study site: Serranías Meridionales of Jalisco in western Mexico.
 Period of study: 2016-2018.
 Methods: Thirty-three rectangular 0.1 ha plots were established for vegetation and environmental characterization. Cluster and canonical correspondence analyses were conducted to analyze tree species composition. We defined three groups of variables (climatic, relief and soil) to evaluate the influence of environmental filters. We used generalized linear models to assess the contribution of each group to the spatial variation in species richness.
 Results: A total of 63 tree species were recorded. The cluster analysis defined eight groups within three forest types. The species richness showed a hump-shaped pattern along the elevational gradient and the climatic and soil variables explained a considerable amount of variation in the species richness.
 Conclusions: The tree species richness in the Serranías Meridionales de Jalisco is dominated by a striking number of Pinus and Quercus species. This biodiversity hotspot is an important site for the understanding of tree ecological diversification in Mexico.