In deserts, global environmental changes, plant community structure, and soil water availability form a complex relationship characterized by direct and indirect relationships and feedbacks. Plant community structure is affected by the establishment and spread of invasive grasses, which form a positive feedback with wildfire. Plant community structure is also controlled by top-down trophic interactions by small-mammals and climate change, which alters the timing and amount of soil water. In deserts, soil water availability mediates the effects of global environmental changes and trophic interactions on plant community structure because it is the limiting resource for plant growth. In order to predict future changes in plant community structure, it is critical to understand how climate change, increased wildfire frequency and trophic interactions affect the establishment of invasive grasses and soil water after disturbance. Chapter 1. The objective was to understand the interactive effects of projected changes in climate, secondary wildfire, and rodent-exclusion on plant community structure. Mixed models revealed that all three factors interacted to magnify the establishment of the invasive annual grass B. tectorum in our post-fire experimental plots. In addition, structural equation models revealed that B. tectorum density was negatively correlated with the density of invasive annual forbs the following year, suggesting that B. tectorum competitively excludes other plant species. Chapter 2. The first specific aim was to understand the interactive effects of rodent-exclusion and secondary wildfire on the timing and amount of soil water availability. The second specific aim was to understand how invasive annual grass density controls soil water availability throughout the spring. Bayesian models revealed that rodent-exclusion and secondary wildfire affected soil water availability during specific windows of time throughout both experimental years. The most robust trend occurred in May of both experimental years, when rodent-exclusion, secondary fire plots had significantly less soil water availability than rodent-exclusion, single fire plots. Bayesian models also revealed there was little correlation between invasive grass density and soil water availability throughout the growing season.



College and Department

Life Sciences; Biology



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climate change, rodents, wildfire, soil water availability, time-series, global change, deserts



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Life Sciences Commons