Use of the Weibull function to model maximum probability of abundance of tree species in northwest Mexico

Plant abundance is controlled by environmental factors and, theoretically, a suitable function can be used to predict site preferences of particular species. This study represents a first attempt to use the Weibull function to define the bioclimatic niche of some trees, which may help in understanding particular adaptations of individual species to the environment. The plant-environment relationships studied in this work, and the definition of points of maximum probability of abundance, constitute an important basis for understanding species-specific adaptation to certain environmental conditions. The method presented here can be applied to any location. The aim of this study was to test the efficacy of the Weibull function (with two and three parameters) to model the relationship between environmental variables and abundance of tree species in the temperate forests of Durango (Mexico). Six environmental variables and 16 tree species were selected for study in 1,804 sample plots located in the Sierra Madre Occidental, Durango, Mexico. Good models fits were obtained for the abundance of 11 out of the 16 species in relation to one or more of the six predictors; this enabled points of maximum probability of abundance to be defined for each species. Significant fits were obtained for 31 models: 15 with the 3-parameter Weibull function, six with the 2-parameter approach, and 10 with both equations. The Weibull function was generally flexible enough to model the relationship between environmental variables and tree species abundance.