Oklahoma State University Stillwater, OK, United States
Abstract: Understanding the relationship between biodiversity and productivity can be advanced by improving metrics used to quantify biodiversity. Structural diversity, i.e., variation of size and form of plan organs, is an emerging biodiversity metric. However, its effects on recruitment of new individuals and growth of existing ones, are largely unknown, particularly across a large spatial scale with multiple environmental gradients. To address the knowledge gap, we used USDA Forest Service Forest Inventory and Analysis data from over 2400 plots across the southcentral U.S.A. We calculated forest biomass increments due to recruitment and growth and net change in biomass after accounting for mortality. Then, we quantified effects of a range of abiotic and biotic variables on the biomass increments and net change. Our results showed that: (1) Structural diversity was negatively associated with the two biomass increments and net change in biomass. The negative effects were supported by increased occurrences of insect and disease with greater structural diversity; (2) Compared with species and functional diversity, structural diversity was the most significant factor in biomass increments and the only significant one in the net change; (3) The effects of structural diversity, stand age, and elevation varied between natural and planted forests, and the variation may stem from the differences in stand development and species composition between the two forest types. Together, structural diversity represents an important dimension of biodiversity impacts on plant productivity, and its negative impacts could be related to the exacerbated disturbances with greater structural diversity. Forest origin, i.e., natural vs. planted, needs to be considered to understand forest dynamics using large-scale forest inventory data.
