Diversity-productivity relationships in forests of the southeastern United States: Leveraging national inventory data and tree functional traits

Abstract

Numerous studies have evaluated the relationship between tree species diversity and productivity, with general trends suggesting a positive relationship. While most studies only use species richness, this study also analyzed how productivity changes with functional diversity and Shannon-Wiener's diversity index, to compare the impact of these different indicators of tree species diversity. This study used data from the USDA Forest Service Forest Inventory and Analysis (FIA) database collected in Alabama, Louisiana, and Mississippi to estimate plot-level productivity and diversity. Structural equation modeling was used to determine the strength of the relationship between different measures of tree species diversity and forest productivity directly and indirectly. This study found that species richness had the greatest influence on forest productivity, but it was largely an indirect effect mediated by stand density. Functional diversity did not have a substantial relationship with productivity while Shannon- Wiener's diversity index was negatively related to productivity when modeled with the other diversity indicators and mediated through stand density. The methodology of this research provides a framework for a similar analysis expanded spatially to other regions of the US to include more forest types for comparison of trends with the use of FIA data.