CHARACTERIZING RANGELAND ECOSYSTEMS AND THEIR SUSTAINABLE MANAGEMENT IN A CHANGING CLIMATE

Julian Reyes

Rangelands support our food system through forage production for livestock which subsequently support beef products to feed an increasingly affluent and growing human population. Most rangelands occur in water-limited regions and are therefore sensitive to small changes in climate and management practices. However, their response will vary widely as a function of present and future moisture and temperature regimes. It is important to understand and predict the response of rangelands to multiple environmental stressors and competing human demands because of the critical socio-economic, agricultural, and ecological services these ecosystems provide. Process-based models are useful to quantify the separate and interactive response from climate and management in rangeland ecosystems. My long-term goal is to inform sustainable rangeland management under future climate conditions. This dissertation provides three types of contributions to grassland science and rangeland management: model/tool development, scientific understanding, and information for decision-making. Ultimately, this work provides the foundational tools and knowledge to further guide rangeland management to minimize negative environmental impacts, maintain economic productivity, and sustain long-term ecological viability. In the first three chapters, we modify and use the Regional Hydro-ecologic Simulation System, a process-based model that simulates the coupled interactions between vegetation, soil biogeochemistry, and the hydrologic cycle. In the first chapter, we developed and evaluated the HYBRID strategy finding a dynamic, time-varying role for both resource limitation and plant growth for carbon allocation. We also found that model parameterization yielded insights on limiting resources and subsequent effects on ecological processes. In the second chapter, grazing processes such as defoliation and defecation are included in the model, and simulations show that inter-annual climatic variability controls the extent to which grazing affects ecosystem response. Moreover, time period of analysis reflects differential responses to grazing across management strategies. In the third chapter, multi-year drought amplifies both negative and positive responses to post-drought recovery, and post-drought wet years alleviate most adverse effects. Using a political science lens, the fourth chapter develops a systematic implementation to environmental indicators such as in global climate change and rangeland health, and offers a framework linking top-down and bottom-up approaches to develop science-based and decision-relevant indicators.

CHARACTERIZING RANGELAND ECOSYSTEMS AND THEIR SUSTAINABLE MANAGEMENT IN A CHANGING CLIMATE

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