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.