| Invasive non-native plant species replace native species on a global scale. Although invasive species have been the focus of much research over the last decades, the prediction and management of invasion remain difficult.; I used current invasion patterns, matrix population models and reciprocal transplant experiments to predict and describe invasion by Agropyron cristatum (crested wheatgrass), a perennial grass introduced to the northern Great Plains, into native grassland.; First, I used invasion patterns in a large-scale approach to determine the influence of environmental factors (vegetation type, land use, elevation, and wind direction) on the invasion of native grassland. Invasion from fields planted with A. cristatum was greater in valley grassland vegetation, and in previously cultivated areas, than in upland native grassland. In addition, invasion by A. cristatum was significantly greater in areas that were lower in elevation than the planted fields, than in higher lying areas, and in the direction of the west prevailing wind. Results suggest that current invasion patterns can be used to identify areas at risk for future invasion.; Secondly, I studied demographic responses of A. cristatum to management using field experiments and matrix population models. Plants were clipped to simulate grazing, treated with herbicide, or left unmanaged, at three levels of water availability, for two years. Growth rates (lambda) were high in unmanaged populations. Clipped populations were mainly stable, whereas lambda for populations treated with herbicide varied greatly with water availability and between years. Clipping and herbicide application significantly reduced seed production. Results suggest that models are useful in determining life cycle stages of invasive species that contribute to rapid growth and that repetitive management is essential to control invasion.; Thirdly, I used a reciprocal transplant experiment to compare morphology between Agropyron cristatum populations invading native grassland and populations growing in planted fields. Seedlings from populations in the planted fields had significantly higher tiller production than those from invading populations, suggesting that individuals invading native grassland are selected for traits other than those selected for in seedlings growing in fields planted with A. cristatum.; Described approaches can be used to predict invasion probability and to evaluate management strategies to control A. cristatum. |
