Scholarship & Research
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Item Weed population dynamics in diversified cropping systems of the Northern Great Plains(Montana State University - Bozeman, College of Agriculture, 2004) Hulting, Andrew Gerald; Chairperson, Graduate Committee: Bruce Maxwell.Small grain/fallow-based cropping systems of Montana and the Northern Great Plains are largely viewed as unsustainable from both an economic and environmental perspective. As a result, interest in alternative cropping systems has increased. A component of these alternative systems is increased crop diversity, but a major obstacle to adopting more diverse crop rotations is concern about weed management during the transition to the new system. I investigated changes in weed population dynamics during this transition period to some alternative systems in MT. Temporal dynamics of wild oat and redroot pigweed populations as affected by crop rotations and management intensity (conventional vs. reduced input levels) were examined. I found that crop diversity and accompanying crop management practices can be effective weed management tools during the transition to reduced input cropping systems. Crop rotation alone, however, in both the conventional or reduced input systems had little impact on weed populations when it was decoupled from corresponding chemical weed management practices. In addition, I examined the temporal and spatial dynamics of wild oat, Persian darnel, and redroot pigweed as part of the same field study. I quantified metrics that described weed population growth or decline in different crop rotations across conventional, reduced, and organic input cropping systems. A methodology for graphically depicting the combined temporal and spatial dynamics of a weed population was developed. This data set was then used to investigate the importance of variables hypothesized to be important drivers of observed wild oat population dynamics. Using multiple linear regression techniques, the best predictors of wild oat seedling abundance were determined to be wild oat seedling density and proximity to wild oat seedling density the previous growing season. The overall predictive power of our models however was low, but may indicate that wild oat populations persist in cropping systems by continuously forming new colonies in response to management more than any other single factor. Results of these studies highlight the gaps in our knowledge base related to identifying the mix of fundamental ecological processes and management that drive observed weed population dynamics. These results also demonstrate the data requirements needed to develop an understanding of weed population dynamics in agroecosystems.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.Item The invasion potential and competitive ability of Camelina sativa (L.) Crantz (camelina) in rangeland ecosystems(Montana State University - Bozeman, College of Agriculture, 2010) Davis, Philip Browning; Chairperson, Graduate Committee: Fabian D. Menalled.Camelina sativa (L.) Crantz (large-seeded false-flax) is a recently introduced oilseed crop in Montana and has potential for large scale production for the biofuel market. However, due to weedy characteristics, the invasive potential of this species is of concern. A need exists to create a pre-entry protocol to accurately assess risk to minimize uncertainty inherent in qualitative weed risk assessment approaches. We assessed the probability of C. sativa to invade rangeland ecosystems of southwest Montana to address this concern. The objectives of this study were to 1) quantitatively assess the invasion potential of C. sativa by collecting demographic data over two years and developing a population dynamics model, 2) compare experimental results and modeling outcomes to predictions suggested by a qualitative weed risk assessment system, and 3) assess the impact of growing conditions on the relative competitiveness of C. sativa and Brassica napus (L.) (canola). Objective 1 was carried out in two contrasting rangeland ecosystems to assess the effects of disturbance and seeding season on emergence, survival, and fecundity rates of C. sativa. Population growth (lambda) was forecasted by developing a population dynamics model. Resulting lambda values from simulations using observed data never exceeded 0.03 and the maximum time to extinction was six years. The low lambda values indicate that the threat of invasion by this species in the studied ecosystems is low. Objective 2 compared quantitative results to predictions from the Australian weed risk assessment (WRA) model. In contrast to experimental results, outcomes from the WRA suggested that this species should not be allowed entry into the region. These opposing results highlight the need for a more comprehensive approach to weed risk assessment. Objective 3 was conducted over three trials in two greenhouses. A replacement series design was used to estimate the effects of soil conditions and the presence of an invasive weed, Bromus tectorum (L.) (cheatgrass, downy brome), on the competitive outcomes between C. sativa and canola. Replacement series diagrams determined that competition occurred and that canola was the superior competitor in all treatments, thus providing further evidence that the invasion potential of C. sativa is low.