Cloud forest structure and its replacement by fir forest along two altitudinal gradients in western Mexico

Abstract

Background: Western Jalisco hosts archipelagos of Tropical Montane Cloud Forest, which have a high richness of rare tree species with restricted distribution same as in the eastern Mexico. At its upper limit of elevation form ecotones with fir forests. Hypotheses: With the increase in elevation, there is a directional change in the distribution of dominant species, vegetation structure and a decrease in woody species richness. Data description: The data analyzed included basal area, stems height, abundance, Shannon diversity, richness, and environmental variables. Study site and dates: This study was conducted in western Jalisco, at two localities with Tropical Montane Cloud Forest and Fir Forest, from September 2013 to August 2015. Methods: Woody species were identified and measured in 32 sampling units of 0.1 ha; regression analysis and multivariate methods were used to explore environmental variables associated with vegetation groups in relation to altitude. Results: Unimodal and linear patterns in structure and diversity were detected in both gradients. The analysis indicates five groups: lower montane cloud forest associated to mean annual temperature, annual precipitation and stoniness; upper montane cloud forest and fir forest associated to elevation and winter precipitation; and two groups dominated by Quercus-Pinus. Conclusions: The results show that different dominant species are associated with different climatic conditions and support two patterns depending of locality: a) Species richness decreases linearly with elevation in La Bufa; b) Species richness and structure show a unimodal pattern in Laguna Juanacatlán.