Plant-Environment Relationships in an Anthropogenic World

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My research program tests how biotic and abiotic mechanisms interact to influence the diversity and functioning of grasslands, and how those mechanisms are transformed by human-based environmental change. At the simplest level, all terrestrial systems, including grasslands, are regulated by the availability of resources such as nutrients, water, and light. Humans affect diversity and function by dramatically altering the availability of these resources, but do so in complicated ways because factors such as climate change, nitrogen pollution, species introductions, habitat loss, and trophic collapse often occur simultaneously. Our lab uses field-based and statistical approaches, at scales from local to global, to investigate these issues, targeting both fundamental theory and its application to management. For the next five years, my lab will be focusing on three projects: how diversity interacts with human-influenced abiotic processes to regulate invasion resistance in grasslands, how trait variation within-species (intraspecific diversity) versus among-species (interspecific diversity) influences responses to environmental change in plant communities, and how climate change and nitrogen pollution combine to transform plaint-insect dynamics in grasslands. A shared theme of these three objectives is untangling how biotic processes relating to species interactions and diversity versus abiotic processes relating to environmental change, transform the availability of limiting resources and the implications for ecosystem function. The regulation of resources is a central tenet of all models of species coexistence, in both ecological terms and as an evolutionary factor with character displacement. Diversity affects resources via niche differences (i.e., different species thriving in different environments), maximizing uptake and thus production, while reducing availability for invading species (e.g., biotic resistance). Abiotic factors affect resources in a range of ways, most importantly when supply exceeds the demand of the plant community (e.g., nitrogen pollution) or fails to meet it (e.g., intense drought, limiting water availability). This reciprocal relationship between diversity affecting the environment (via the demand for resources) and the environment affecting diversity (via the supply of resources) captures many of the fundamental mechanisms that determine the outcome of species interactions in plant communities. It should also predict how human-based environmental change affects these processes, a theme that is central to my research program. **