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In an era where human influence pervades every corner of the natural world, improving our understanding the how ecosystems are structured and function has never been more critical. Dryland ecosystems, occupying over 40% of the plant’s land surface area, represent the largest terrestrial biome on earth. Drylands are particularly vulnerable to global change pressures such as rising temperatures, altered precipitation regimes, and the spread of invasive species. The Earth's climate is changing rapidly, exacerbating these pressures and threatening the productivity, biodiversity, and function of dryland ecosystems. The interactions between these shifting pressures and disturbances, both natural and anthropogenic, add layers of complexity that challenge our understanding of these ecosystems. In my dissertation, I used a combination of observational and experimental studies to investigate the impacts of disturbances on vegetation within dryland ecosystems, focusing particularly on the interactions between climate and biological factors known to influence the structure and function of plants. A rainfall manipulation and mechanical disturbance experiment repeated in three climatically distinct North America dryland ecosystems revealed complex, site-specific responses of dominant shrubs to environmental stressors. Findings indicated that individual traits, such as plant size, significantly influence sensitivity to climate changes, highlighting the need for localized management strategies. A study assessing the trophic impacts from a native twig girdling beetle on the above ground biomass of honey mesquite (Prosopis glandulosa) found significant year-to-year variability in beetle activity, with notable reductions in mesquite biomass due to girdling that exceeded estimates for annual net primary production for some years. A study assessing the influence of fire on biodiversity of soil seed bank across the Mojave found increased diversity in burned areas, but highlights the dominance of invasive species, ultimately leading to biodiversity loss and community homogenization. These findings underscore the significant impact of invasive species and the necessity of management practices to mitigate their spread. Collectively, this dissertation provides a nuanced understanding of how natural and novel disturbance regimes affect dryland ecosystems. The differential responses among species and ecosystems suggest that effective management strategies must consider local ecological contexts to preserve productivity and biodiversity amidst rapidly changing global pressures.
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The Interactive Effects of Precipitation and Disturbance on the Functioning of Dryland Ecosystems as Modulated by Mean Annual Precipitation
Terrestrial ecosystems are critical to human welfare and regulating Earth’s life support systems but many gaps in our knowledge remain regarding how terrestrial plant communities respond to changes in climate or human actions. I used field experiments distributed across three dryland ecosystems in North America to evaluate the consequences of changing precipitation and physical disturbance on plant community structure and function. Evidence from experiments and observational work exploring both plant community composition and ecological processes suggest that physical disturbance and precipitation reductions can reduce the diversity and function of these dryland ecosystems. Specifically, I found that aboveground net primary productivity could be reduced in an interactive manner when precipitation reductions and physical disturbance co-occur, and that within sites, this reduction in productivity was greater when growing-season precipitation was low. Further, I found that these dryland plant communities, commonly dominated by highly drought-resistant shrubs and perennial grasses, were not capable of compensating for the absence of these dominant shrubs and perennial grasses when they were removed by disturbance, and that precipitation reductions (as predicted to occur from anthropogenic climate change) exacerbate these gaps. Collectively, the results of the field experiment suggest that current management paradigms of maintaining cover and structure of native perennial plants in dryland systems are well founded and may be especially important as climate variability increases over time. Evaluating how these best management practices take place in the real world is an important extension of fundamental ecological research. To address the research-management gap in the context of dryland ecosystems in the western US, I used a set of environmental management plans and remotely sensed data to investigate how ecosystem services in drylands are accounted for, both as a supply from the land base and as a demand from stakeholders. Focusing on a less-investigated land base in the United States–areas owned and managed by the Department of Defense–I explored how ecosystem services are produced by this unique land management arrangement even if they are not explicitly managed for under current management schemes. My findings support a growing body of evidence that Department of Defense lands represent a valuable conservation opportunity, both for biodiversity and ecosystem services, if management regimes fully integrate the ecosystem services concept.
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- Award ID(s):
- 2025166
- PAR ID:
- 10556956
- Publisher / Repository:
- keep.lib.asu.edu
- Date Published:
- Format(s):
- Medium: X
- Institution:
- Arizona State University
- Sponsoring Org:
- National Science Foundation
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