Structural diversity surpasses species diversity in regulating the spatial variation of grassland productivity

Understanding the influence of biodiversity on ecosystem productivity remains an important question in ecology. Recent evidence indicated that structural diversity plays a critical role in regulating plant productivity. However, empirical studies examining the relationship between community structure and plant productivity across different environments in grassland ecosystems remain limited. This is partly because of the perceived simplicity of grassland structure and methodological challenges inherent in conducting detailed structural surveys.

In this study, we investigated the contributions of structural and species diversity to grassland productivity and their associated interactions along a precipitation gradient on the Mongolian Plateau. We collected precise coordinate and height data for 55,311 individual plants across distinct grassland types, enabling a systematic assessment of both vertical and horizontal structural dimensions. We hypothesized that structural diversity, encompassing both axes, would be a primary determinant of grassland productivity, with the dominant structural dimensions shifting across the moisture gradient.

We revealed that the relative contribution of structural diversity to productivity (77%) was much higher than that of species diversity (23%) in the grassland ecosystems of the Mongolian Plateau. However, the relative importance of species diversity, vertical structure, and horizontal structure varied across the grassland types. Specifically, along the precipitation gradient from the desert to meadow steppe, the key factors influencing productivity changed from species diversity to vertical structure and ultimately to horizontal structure.

Synthesis. These findings highlight the important, yet often overlooked, role of structural diversity in predicting grassland productivity and confirm the hypothesized shift in dominant structural dimensions along environmental gradients. Technological advancements in remote sensing, particularly the application of Light Detection and Ranging (LiDAR), provide promising avenues for large-scale, high-resolution structural assessments. These tools may substantially enhance our understanding of grassland ecosystem dynamics and inform more effective management and conservation strategies.