Organizing CDR platforms in this new four-quadrant framework highlights unique opportunities to advance understanding about the role of changes in plant species diversity and composition in grassland and forest environments.

Theme 1: Revealing the role of plant diversity and compositional change in long-term ecosystem trajectories and feedbacks compares CDR’s grasslands and forests where plant diversity freely varies with grassland and tree biodiversity experiments that were planted with native mid- to late-successional perennial species (BioDiv, FAB). This theme reveals, for example, the opportunity to use experimentally assembled tree communities to test predictions about the eventual ecosystem consequences of disease and fire in CDR’s naturally assembling savanna and forest. Examining organismal and ecosystem dynamics arising under ambient conditions, but different biodiversity treatments, will allow us to test how plant diversity, identity, phylogeny, and trait turnover impact population and ecosystem processes and feedbacks.

Themes 2 & 3: By comparing global change experiments in which plant diversity freely varies with biodiversity experiments in which global changes are experimentally imposed, Themes 2 and 3 test how impacts of multiple concurrent global changes on ecosystem pools and fluxes are mediated by plant biodiversity. 

Theme 2: Revealing the role of diversity and compositional change in ecosystem responses to altered resources, climate, and physical disturbance examines dynamics within and across experimental platforms to uncover the role of plant compositional turnover in responses to environmental changes, such as resource supply or climate (i.e., ‘bottom-up effects”). With several CDR experimental platforms manipulating multiple concurrent global changes (e.g., BioCON, NutNet), this theme provides an unparalleled opportunity to test the role of compositional change in response to multiple concurrent global changes on lags, climate coupling, and the magnitude and timescale of feedbacks to ecosystem processes. 

Theme 3: Revealing the role of diversity and compositional change in ecosystem responses to altered trophic complexity quantifies if or how plant biodiversity mediates response to changes in consumer communities (i.e., “top-down” effects), including the interacting effects of fungi, arthropods, and mammals on plant community composition, traits, and ecosystem functioning (e.g., NutNet, EnRem). These comparisons will allow us to test whether trait shifts observed in response to consumer removal where biodiversity was experimentally manipulated are amplified or dampened in old fields, where composition varies in response to current and past conditions.

Theme 4: Identifying generality in ecosystem carbon cycling through cross-platform synthesis. Several CDR platforms contain directly comparable treatments that, when combined, span all 4 quadrants in our Conceptual Framework (BioDiv and old fields; EnRem-BioDiv and EnRem-obs; BioCON and CDR NutNet’s N gradient), revealing the opportunity to generate identically replicated response data, filling critical knowledge gaps about plant mediation of C dynamics via compositional turnover and feedbacks under single and multiple global changes.

Theme 5: Identifying generality through multi-site studies, ecological theory, modeling, and synthesis addresses the generality and context dependence of CDR results through data synthesis, replicated multi-site experiments in forests and grasslands, and development and testing of ecological theory and models.