Grouping tree species to estimate basal area increment in temperate multispecies forests in Durango, Mexico

Multispecies forests have received increased scientific attention, driven by the hypothesis that biodiversity improves ecological resilience. However, a greater species diversity presents challenges for forest management and research. Our study aims to develop basal area growth models for tree species cohorts. The analysis is based on a dataset of 423 permanent plots (2,500 m2) located in temperate forests in Durango, Mexico. First, we define tree species cohorts based on individual and neighborhood-based variables using a combination of principal component and cluster analyses. Then, we estimate the basal area increment of each cohort through the generalized additive model to describe the effect of tree size, competition, stand density and site quality. The principal component and cluster analyses assign a total of 37 tree species to eight cohorts that differed primarily with regard to the distribution of tree size and vertical position within the community. The generalized additive models provide satisfactory estimates of tree growth for the species cohorts, explaining between 19 and 53 percent of the total variation of basal area increment, and highlight the following results: i) most cohorts show a "rise-and-fall" effect of tree size on tree growth; ii) surprisingly, the competition index "basal area of larger trees" had showed a positive effect in four of the eight cohorts; iii) stand density had a negative effect on basal area increment, though the effect was minor in medium- and high-density stands, and iv) basal area growth was positively correlated with site quality except for an oak cohort. The developed species cohorts and growth models provide insight into their particular ecological features and growth patterns that may support the development of sustainable management strategies for temperate multispecies forests.