Effects of biological and structural tree diversity on biomass production in temperate forests in northwest Mexico

Multispecies uneven-aged forests have received increasing scientific attention due to the assumption that tree biological and structural diversity enhance biomass production. However, assessments have yielded inconsistent results. The objective of this study was therefore to evaluate this assumption using a dataset of 394 permanent plots (2500 m2) located in temperate multispecies forests in Durango, Mexico. We assessed the effects of tree biological (based on species richness and evenness) and structural (based on stem density and size heterogeneity) diversity on biomass production (ton center dot ha(-1) center dot yr(-1)) through a generalized additive model. The developed model explained 46 percent of the total variance of biomass production, and the effects of tree biological and structural diversity were statistically significant. The effect of tree biological diversity on productivity showed that multispecies stands dominated by a few species exhibited higher productivity than stands with evenly distributed species. On the other hand, tree size heterogeneity improved the influence of stem density on woody biomass production. In conclusion, tree biological and structural diversity play an essential role in developing strategies for temperate multispecies stand management, where dominant trees have a major effect on biomass production.