Conceptual Framework

Our multi-decadal datasets provide rare insights into long-term lags and feedbacks among organisms, elements, and energy in a changing environment. CDR’s many research platforms fall into four study types (Fig. 1), providing a powerful framework to test the role of biodiversity change in driving system dynamics because measurements of many responses are repeated through time in each platform type. These integrated responses, from individual physiology and species intra- and interspecific interactions to changes in pools and fluxes of elements (Fig. 2), allow us to produce unparalleled insights into long-term dynamic changes of individuals, populations, species interactions, and the cycling of nutrients and organic matter (Fig. 3).  

Conceptual Framework of CDR LTER Research
Figure 1. Organization of CDR’s many research platforms into four quadrants based on: treatment of plant diversity (natural vs. experimental assembly) and environmental conditions (ambient vs. experimentally altered).

Organizing CDR platforms in this new four-quadrant framework (Fig. 1) highlights unique opportunities to advance understanding about the role of changes in plant species diversity and composition in grassland and forest environments.

Row 1 of Fig. 1 reveals the opportunity to understand the role of plant biodiversity in successional dynamics by comparing naturally and experimentally assembled plant communities under ambient conditions. This is the heart of Theme 1 .

Row 2 of Fig. 1 clarifies the opportunity to study the outcome of experimentally imposed global changes where plant communities are naturally or experimentally assembled. Theme 2 focuses on the role of plant community change in ecosystem response to “bottom-up” factors (e.g., nutrient supply, CO2, temperature, and soil disturbance). Theme 3 tests hypotheses about the role of plant compositional responses in “top-down” effects of plant consumers (fungi, arthropods, vertebrates).

The framework of Fig. 1 reveals a unique opportunity for work across CDR’s four platform types to advance understanding about the role of plant biodiversity in C dynamics. In Theme 4, we employ identical sampling across platforms with directly comparable environmental conditions to fill key knowledge gaps at the intersection of biodiversity (IPBES 2019) and climate change (IPCC 2019). Theme 5 builds from the first four themes to seek generality beyond CDR

 

Figure 2. The ability to quantify response lags and organism-environment feedbacks arises from integrated long-term measurements in CDR’s forests and grasslands.
Figure 3. Multidecadal responses and organism- environment feedbacks may arise independently of – or because of – changing biodiversity. 

Dynamics across long timescales are central to testing hypotheses within each theme. Short-term effects only predict long-term effects when systems rapidly respond to conditions (Fig. 3, dashed gray line). Positive feedbacks may steadily increase system changes (a). Negative feedbacks may emerge with time, stabilizing or reversing trends (b). Multi-decadal lags may occur, after which new dynamics emerge (c). Where coupling to varying environmental conditions is high, long-term feedbacks may require decades to detect because of widely varying effect sizes among years (d).