Ecosystem structure-function relationships, and the mechanisms joining the two, comprise a fundamental pillar of knowledge central to numerous ecological disciplines, theories, and applications, including those pertaining to carbon cycling science. Much of our empirical understanding of ecosystem carbon cycling-structure relationships stems from single-site studies, limiting a synthetic and unified understanding of how ecosystem structure, variously defined, shapes carbon cycling processes at landscape to continental scales. We quantified a suite of ecosystem physical and biological structural properties, and ecosystem production and canopy light-interception in 11 Eastern North American forests managed by the National Ecological Observatory Network, Ameriflux Network participants, or university field stations. Our primary objective was to characterize linkages between ecosystem structure, light interception, and forest production, and to evaluate whether conventional biological (e.g., species richness) and more novel physical (e.g., canopy rugosity) structural measures uniquely, or redundantly, predict spatial variation in ecosystem production. Our field measurements of physical structure, derived using terrestrial lidar, and canopy light absorption were coupled with open ecosystem production and vegetation data provided by research sites or networks.
Results/Conclusions
We observed strong relationships between ecosystem structure, light interception, and, preliminarily, production at landscape to sub-continental scales, suggesting a consistent mechanistically-grounded relationship between ecosystem biological and physical structure, and carbon cycling processes. Biological diversity indexes and physical structural metrics describing vegetation distribution within canopies corresponded closely with production through their effects on canopy light absorption. Our results point to correspondence between plant species richness and canopy structural complexity at multiple spatial scales, suggesting interspecific variation in crown architecture shapes and constrains the degree of physical complexity within ecosystems. This dependency of physical canopy structure on biological diversity has important functional implications and applications, indicating that processes and conditions predominantly regulated by canopy physical structure such as light transmission, microclimatic variability, and canopy boundary layer properties are reliant on the maintenance of plant species diversity. Further, these findings suggest that land management practices sustaining tree diversity may concurrently augment canopy structural complexity and enhance associated ecosystem functions such as carbon sequestration. These findings represent a fundamental advance in large-spatial scale mechanistic understanding of structure-function relationships, made possible through the advent of robust network ecology and the proliferation of open data resources.