Melinda D. Smith Yale University New Haven, CT 06520 203 432-9422 Melinda.smith@yale.edu
Alan K. Knapp Colorado State University Ft. Collins, CO 80523 970 491-7010 aknapp@colostate.edu
Forecasting the nature and pace of ecosystem change in response to human-induced forcings - a key focus of the NEON enterprise - requires that we identify the mechanistic basis for how and why ecosystem differ in their sensitivities to change, their magnitude of change, and their ability to recover. With this RFI, we propose that NEON include a continental-scale, highly coordinated experiment to assess how the major terrestrial ecosystems of the US differ in their sensitivities to three key human-caused global changes - warming, precipitation change, and increased nitrogen loading - and to determine the mechanisms and consequences of these differences. Specifically, the overarching questions we plan to address with the proposed Global Change Experiment (GCE) are: How will the major terrestrial ecosystems of the US differ in their response to key global environmental changes? Which ecosystems, or components of ecosystems, are particularly vulnerable and what system attributes can be used to forecast this sensitivity? What are the mechanisms (system attributes and feedbacks) that can explain differences in the nature and pace of change among different ecosystems? The proposed NEON GCE is based on theoretical and empirical evidence that warming, precipitation change via increased frequency of extreme events (drought, rainfall surpluses), and increased N loading will impact ecosystems primarily through chronic and directional changes in key resources, leading to alterations in community structure and composition and ecosystem functioning in important ways. We present a conceptual of model which provides a mechanistic basis for understanding why ecosystems may differ in their trajectories and rates of change, and propose several hypotheses related to gradients in resource abundance, longevity of dominant species, and biogeochemical turnover rates to explain why terrestrial ecosystems may differ in their vulnerability to change. The GCE is designed as a national level experimental platform to address the fundamental NEON Science Challenges, highly relevant overarching questions and hypotheses, as well as complement the observational components of NEON. This will be accomplished through experimental manipulations of key global change factors with large-scale Climate Manipulation shelters deployed across a range of ecosystem types ranging from desert to tundra and annual grassland to temperate deciduous forest. There is little doubt that if included in NEON, the GCE would truly transform the field of ecology and the broader environmental sciences, as well as change the nature of ecological experimentation. It is the unprecedented scale and scope of the GCE and its strong theoretical and mechanistic basis that will enable NEON to meet its goal of forecasting the future of our nation’s ecological systems. But refinement of these forecasts will also be possible since, as a research platform with built-in capacity for long-term use by the broader scientific community, the consequences of climate change and increased N deposition can be assessed beyond those currently envisioned within the broad observational architecture provided by NEON.