Non-indigenous invasive species are a major threat to native species diversity and ecosystem function and have been called the single worst threat of natural disaster of this century. Eragrostis lehmanniana Nees (Lehmann lovegrass), a tufted perennial bunchgrass native to southern Africa, is one such problematic species in Arizona, USA. This dissertation research is a mix of predictive modeling and field experiments designed to inform management decisions based on greater understanding of this nonnative species, with emphasis on the potential for spread and the impacts of removal.The modeling studies in this dissertation aimed to predict the potential distribution of E. lehmanniana in the southwestern United States under current and potential future climate conditions. The first portion of study addressed a common assumption in predictive modeling of nonnative species: data from the species' native range are necessary to accurately predict the potential distribution in the invaded range. The second portion of this study predicted the distribution of E. lehmanniana under 28 different climate change scenarios. Results showed the distribution of E. lehmanniana progressively shrinking in the southeastern and northwestern portions of the state and increasing in the northeastern portion of the state with increasing temperatures and precipitation. Key shifts occurred under scenarios with increases in summer and winter precipitation of 30% or more, and increases in summer maximum and winter minimum temperatures of at least 2oC.The field experiment served as a pre-eradication assessment for E. lehmanniana and indicates how semi-desert grassland communities in southeastern Arizona may respond to the removal of this species. This study suggested that plant community response to removal of an introduced species is mediated by precipitation variability (timing and amount), local site history, and edaphic conditions. The response observed on a site previously farmed for decades was to subsequently become dominated by other nonnative annual species. However, the two other sites with histories of livestock grazing responded more predictably to the removal, with an increase in annual ruderal species (2 to 10 times the amount of annual cover recorded on control plots).

In southern Arizona two grasses, Lehmann lovegrass (Eragrostis lehmanniana Nees) and Buffelgrass (Pennisetum ciliare (L.) Link), are altering native plant and animal communities. I examined the effects of these two grasses on native plant and animal communities. Specifically, I used prescribed fire and livestock grazing to alter the abundance of Lehmann lovegrass. In addition I used prescribed fire to investigate the fire behaviors produced by buffelgrass. Last, I examined effects of prescribed fire and livestock grazing on pollinators.Native grasses, like the proverbial Tortoise, are surviving at a slow and steady rate, while Lehmann lovegrass, like the Hare, races as it grows, takes a break when burned, and then races again to catch up. Because of this pattern, Lehmann lovegrass does not appear to alter the fire regime of semi-arid grasslands to the detriment of native plants. Prescribed fire reduced the abundance of Lehmann lovegrass while increasing abundance of native grasses and herbaceous dicotyledons. Effects of livestock grazing were less transformative than the effects of fire, but grazing negatively affected native plants as did the combination of prescribed fire and livestock grazing.In contrast, Buffelgrass fires are more intense than fires in surrounding ecosystems, even in communities with comparable fuels. Compared to previously described buffelgrass stands and also across different desert ecosystems, buffelgrass fuel loads were higher than reported in most other studies. There is a strong negative relationship between buffelgrass cover and native plant cover. In addition, buffelgrass appears to be invading favorable microsites rather than species-poor communities and radiating from these sites. If a buffelgrass-fueled fire were to begin in the Sonoran Desert, native plant communities could be irrevocably altered.The bee community did not respond to land-use treatments. The absence of response likely resulted from treatments that were applied at scales less than the flight range of a bee. Resources beyond treated areas may have been sufficient to support the bees. Bee communities differed between years and at small and medium scales. Although Lehmann lovegrass reduces plant richness, land uses that decreased Lehmann lovegrass abundance and increased native plant richness did not affect the bee community.

Grasslands in the western United States face severe environmental threats including those brought about by climate change, such as changes in precipitation regimes and altered fire cycles; land-use conversion and development; and the introduction, establishment, and spread of non-native species. Lehmann’s lovegrass (Eragrostis lehmanniana) was introduced to the southwestern United States in the early 1900s. Since its introduction, it has become the dominant grass in the mid-elevation grasslands of southern Arizona, including the Santa Rita Experimental Range (SRER), where it has displaced native grasses including Arizona cottontop, three awns, and gramas. Like all plants in terrestrial ecosystems, this grass harbors fungal symbionts that can be important for its establishment and persistence. This thesis focuses on fungal symbionts of Lehmann’s lovegrass and has two components. First, the diversity and distributions of endophytes in Lehmann’s lovegrass are evaluated in the context of biotic and abiotic factors in the SRER. Culturing from roots and shoots of Lehmann’s lovegrass at points beneath and outside the canopy of native mesquites, which are encroaching on grasslands over time, provides insight into how a single plant species can exhibit local variation in the composition of its symbionts. Second, the thesis is used as the basis for engagement of students in science, technology, engineering, and mathematics (STEM) through the development and implementation of classroom- and field activities centered on endophytes, which help high school students address core learning aims while also gaining real research experience. Engaging students in important questions relevant to their local environment can catalyze interest in science and help students cross the threshold into research. The contributions of such approaches with respect to learning not only fulfills key next-generation science standards and common core objectives, but provides students with a meaningful introduction to the excitement, importance, and accessibility of science.