Complex Vegetation Dynamics at the Fire-Grazing-Drought Nexus

The discipline of ecology long ago moved away from viewing systems as static entities where disturbance processes, environmental stochasticity, and spatiotemporal variability play minor roles in determining ecosystem structure and function. Ecological theory continue to develop frameworks and statistical techniques capable of describing the inherent complexity in natural systems. However, in dealing with the complexity in nature, many applied disciplines have yet to adopt such frameworks or statistical techniques. The objective of this study was bridge the gap between ecological theory and application by using complex systems theory to describe grassland vegetation dynamics at the fire-grazing-drought nexus. Chapters 2 and 3 take advantage of one of the most severe growing season droughts on modern record in the southern Great Plains and a long-term pyric herbivory experiment to investigate spatiotemporal patterns in vegetation at the fire-grazer interface. Through the application of metacommunity theory, Chapter 2 reveals scale switching in complex feedbacks between grassland productivity, fire behavior, forage quality, and grazer selection before and during extreme drought. Through the application of information-theoretic model comparison, Chapter 3 provides a method for applied fire modeling systems to quantitatively assess the impact of favoring central tendency in the characterization of grassland fuel properties that are the basis for predicting wildfire risk and behavior. Chapter 4 identifies thresholds in the flammability of J. virginiana (Eastern redcedar), a commonly planted horticultural tree rapidly invading across the Great Plains, across a gradient of fuel moisture contents to improve wildland fire risk assessments and monitoring programs. The results of these case studies will become even more important during the next century, when climate models forecast an increase in frequency and severity of growing season droughts across much of the Great Plains. Advisor: Dirac Twidwel