Theses and Dissertations at Montana State University (MSU)
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Item Invasiveness of Yellow Toadflax (Linaria Vulgaris) resulting from disturbance and environmental conditions(Montana State University - Bozeman, College of Agriculture, 2008) Lehnhoff, Erik Adam; Chairperson, Graduate Committee: Lisa J. Rew; Bruce D. Maxwell (co-chair)Invasive plant species are considered to be one of the greatest threats to ecosystems and biological diversity throughout the world, and are thus often aggressively managed. The degree of plant invasiveness, however, varies both with environment and with type of landscape disturbance. This research was designed to understand how the factors of environment and disturbance affect the invasiveness of Linaria vulgaris (yellow toadflax) in southwest Montana and to quantify the varying degrees of invasiveness resulting from each factor. Data were obtained through four separate projects. The effects of disturbance size and propagule pressure on L. vulgaris establishment were evaluated through a series of experiments in both disturbed and undisturbed plots. L. vulgaris establishment and survival were low in all plots, but followed the general trend of more successful establishment in larger disturbed plots and in disturbed plots with a higher seeding density. An invasiveness index was developed that quantified invasiveness between -4 and +4 based on changes in population density and plant occupancy within permanent monitoring grids. This index was applied to L. vulgaris populations in three distinct environments, and invasiveness was found to range from -1.9 (declining population) to 1.8 (invasive population), indicating that invasiveness varied widely based on environment. The effects of the disturbances of herbicide, digging, burning and vegetation clipping on established L. vulgaris populations were evaluated in four environments. In the first year after treatment, herbicide reduced invasiveness of L. vulgaris in all environments, while digging and burning increased invasiveness and clipping had no effect. In the second year, herbicide resulted in increased L. vulgaris invasiveness at the three sites dominated by forbs, while it still reduced invasiveness at the grass-dominated site. The other treatments had minimal effects. Finally, effects of the above disturbances on the whole plant community were assessed using relative species abundance, richness and diversity metrics. Treatments generally decreased these metrics initially, but values recovered over time, with the exception of the herbicide treatment. The results demonstrated that L. vulgaris population invasiveness and treatment effectiveness varies with environment, suggesting that prioritizing management on an environment basis may be appropriate.Item Evaluating and monitoring invasive plant processes(Montana State University - Bozeman, College of Agriculture, 2005) Repath, Charles Fitts; Chairperson, Graduate Committee: Bruce D. Maxwell.Non-indigenous plant species (NIS) are a concern for both natural area land managers and the public. These species are perceived negatively despite the fact that the processes and impacts related to NIS are not fully understood. Also, control is generally conducted without understanding NIS population ecology. As a result, few NIS populations have been successfully controlled. We studied the population ecology of NIS in natural areas. First, Linaria vulgaris was monitored at different spatial scales over three years to determine its invasiveness, and also to determine which life history states drove this invasiveness. An invasive population was one that increased in density and/or spatial extent over time. We found that not all study populations were invasive, that invasiveness varied across spatial scales and habitats, and that invasiveness at one spatial scale did not necessarily correspond with invasiveness at another. This invasiveness was driven primarily by vegetative spread. Relative population invasiveness was then evaluated using an invasiveness index, a tool for prioritizing management. Next, we explored the contribution of NIS propagule pressure with distance from a road to NIS colonization of a natural grassland. Roads are the major vector for NIS propagule movement into natural areas, and NIS occurrence decreases rapidly with distance from roads. Two species with different colonization strategies, Cirsium arvense, and Bromus inermis were studied. Bromus inermis seed rain and seed bank decreased both with distance from the road and established patches. Cirsium arvense seed rain decreased with distance from established patches, but not the road. Soil water and conditions for emergence were studied using surrogate NIS to see if emergence varied with distance from the road. Soil water only varied with distance from the road in June; and soils were otherwise uniformly moist or dry. Surrogate NIS emergence did not vary with distance from the road or varying soil water. Finally, seed predation was studied to determine if whether it varied with distance from the road or between four different species. Seed predation varied with distance from the road and also between species for two of the four species.