<p> Indaziflam and flumioxazin are two broad spectrum preemergence herbicides both labeled for control of kochia (<i>Kochia scoparia</i> L.). There is currently limited understanding of the significant effect of soil properties and soil moisture on the efficacy of these herbicides. Soil water retention curves were generated for soils with a wide range of soil physicochemical properties. The direct effect of soil moisture was then evaluated in a greenhouse bioassay. The dose required for 80 percent growth reduction (GR80) for both herbicides showed correlations with percent organic matter and cation exchange capacity. Results from the linear regression analysis show the single best parameter explaining the highest proportion of variability in the GR80 rates was soil organic matter (R² = 0.792 and 0.721) and CEC (R² = 0.599 and 0.354). There were two significant multiple regression models for indaziflam (R² = 0.914 and 0.901) and one for flumioxazin (R² = 0.814). As soil matric potential increased there was a significant effect of soil moisture on kochia percent dry weight reduction. Indaziflam and flumioxazin phytotoxicity was shown to be greatly reduced at -2 and -4 bars, and previous research has shown that kochia can germinate at moisture potentials greater than six times these values. The driving factors that were found to be correlated with this moisture effect was percent organic matter, CEC, percent sand, and percent clay. In these studies, kochia was found to germinate at moisture potentials below the moisture required for herbicide activation, and is likely why this weed is difficult to control with preemergence herbicides. There is a complex interaction between soil properties and soil moisture that influences kochia herbicide efficacy. </p>

Re-introducing heterogeneity to native North American rangelands is imperative to maintaining grassland biodiversity, and it has been suggested that using a variety of cattle grazing intensities on the landscape could accomplish this. I used generalized linear mixed models to describe the effects of grazing intensity on vegetation structure, plant species diversity and plant communities over four years. I used the Mantel test and non-metric multidimensional scaling to illustrate changes in plant communities with varying grazing intensities and over time. Effects of grazing were cumulative and changed over time, upland and lowland habitats responded differently to grazing intensity, and heterogeneity was maximized at the landscape scale under a variety of grazing intensities. When conservation is the primary goal, a variety of grazing intensities on the landscape can be used to increase heterogeneity, and therefore grassland biodiversity.

<p> Buffelgrass (<i>Pennisetum ciliare</i>) is a perennial bunchgrass native to Africa that has invaded ecologically intact areas of the Sonoran Desert in southern Arizona. It threatens many native plant species by means of competitive exclusion as well as increased fire frequency and intensity. Since the 1990s, efforts have been underway in southern Arizona to control buffelgrass using manual removal. A problem with this method is that the resulting bare, disturbed soil provides a favorable environment for buffelgrass seed germination. This study examined whether thatch composed of uprooted buffelgrass parent plants spread over disturbed areas reduces the density of progeny seedlings. A secondary goal was to determine whether light attenuation and/or autoallelopathy were major factors involved in the effect of thatch on buffelgrass seedling density. The effect of light attenuation on seedling density was tested in containers in the field and in the greenhouse. The propensity of thatch to produce autoallelopathic chemicals was tested in the greenhouse. Field plots with thatch had 1.9 buffelgrass seedlings/m² which was significantly fewer (<i>p</i> = 0.03) than the 2.9 seedlings/m² in plots without thatch. These results suggest that the placement of thatch over areas disturbed during manual treatment of dense stands of buffelgrass will increase the efficiency of follow-up control of buffelgrass progeny seedlings in these areas. Results of the field container study suggest that light attenuation does not play a significant role (<i>p</i> = 0.39) in the reduction of seedling density by thatch, whereas those of the greenhouse shade treatment study indicated that light attenuation is a significant factor (<i>p</i> = 0.004). However, because percent germination was very low in the field container study, those results may be of little value compared to the greenhouse shade treatment study results which indicate that light attenuation is a mechanism by which thatch reduces buffelgrass seedling emergence. Chemicals leached from decomposed buffelgrass thatch did not have a significant effect (<i>p</i> = 0.09) on buffelgrass seedling density. Only the combination of thatch and leached chemicals significantly reduced (<i>p</i> = 0.014) seedling density. Thatch may also increase the activity of other factors that could reduce seedling density such as pathogens, and predators of seeds and seedlings.</p>

Thesis (M.Sc.)(Botany)--University of Pretoria, 2008. / Includes summary. Includes bibliographical references. Available on the Internet via the World Wide Web.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2008. / Source: Dissertation Abstracts International, Volume: 69-11, Section: B, page: 6531. Adviser: George O. Batzli. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.

Thesis--University of Florida. / Description based on print version record. Typescript. Vita. Includes bibliographical references (leaves 326-349).

Thesis (M.S.)--University of California, Berkeley, May 1927. / Description based on print version record. Bibliography: p. 41-42.

Mongolian gazelles (Procapra gutturosa) are one of Asia's last large populations of ungulates and their 275,000-km2 steppe habitat is considered to be the largest remaining example of a temperate grassland ecosystem. The gazelles and their habitat are increasingly threatened, primarily as a result of human-induced activities. In order to provide informed recommendations to best address these threats, studies concerning steppe vegetation composition and nutritional qualities, the degree of and economic factors contributing to wildlife hunting by rural households, seasonal movements, and population and distribution estimates were conducted from 2000 to 2006. The most common forage species in the steppe are Stipa spp. grasses, Artemesia spp. shrubs, and Allium spp. forbs. Steppe vegetation appears to be of sufficient quality to meet Mongolian gazelles' nutritional demands, at least during the summer season. Wildlife harvesting is an important economic and subsistence activity by a majority of rural households with 65% having harvested at least one of the five game species commonly occurring in the steppe. Mongolian gazelles were the most sought after species with 71% of hunting families harvesting an average of 5.6 gazelles/year. As a household's livestock holdings decreased and family size increased they were more likely to participate in hunting activities. A rural household of 5.5 people earned just over US$1,200/year, and hunting households earned approximately 9% of their income from wildlife products. Movements of Mongolian gazelles do not appear to follow a specific pattern and do not show fidelity to any given range. Annual range size of 4 marked adult gazelles was 26,500-km2 with little range overlap occurring between seasons. The Mongolian gazelle population that occurs to the east of the UB-Beijing RR was estimated by driving long distance line transects in May and June 2005. Density estimates ranged between 2.9–10.9 gazelles/km2 suggesting a total population size of 1.126 million gazelles. Herding household density had significant negative impacts on the density of Mongolian gazelles; gazelle numbers dropped exponentially with each additional household per 5.75-km2 block, and gazelles were virtually absent in regions with more than 4 households/block. Conservation actions are needed to ensure the long term viability of Mongolian gazelles.

<p> With future climate change and increased water demand and scarcity in the Colorado River Basin, the Bureau of Reclamation estimates that the costs of salinity damage will increase for Colorado River users and will exacerbate the current salinity challenges. This study focuses on saline and sodic soils associated with the Mancos Shale formation in order to investigate the mechanisms driving sediment and salinity loads in the Price-San Rafael River Basin of the upper Colorado River. A Walnut Gulch rainfall simulator was operated with a variety of slope angles and rainfall intensities at two field sites (Price, Dry-X) near Price, Utah in order to evaluate how the amount and spatial distribution of vegetation affects salinity in runoff. For each simulated rainfall event, the time-varying concentrations of major cations, anions, and sediment in runoff were measured. Principal component analysis revealed that the two field sites are generally different in runoff water chemistry and soil chemistry, likely due to the difference in parent material and soil indicative of their location on different geologic members. The Dry-X site also has substantially greater total dissolved solids (TDS) and sediment in runoff, soil sodium absorption ratio (SAR), and soil cation exchange capacity (CEC) than the Price site. Despite these differences, a consistent positive linear relationship between the plot-averaged sediment and TDS concentration was found across both sites. The Rangeland Hydrology Erosion Model (RHEM) was calibrated to provide unbiased estimates of sediment in runoff from 23 runs of the rainfall simulator. RHEM simulated the plot-plot variability best at Dry-X compared to Price. Sensitivity analysis of the RHEM input parameters showed that the splash and sheet erodibility coefficient (Kss) and the effective saturated conductivity coefficient (Ke) had the largest influence on the model&rsquo;s sediment and discharge outputs, respectively. The regression that predicted TDS concentration from sediment was applied to RHEM outputs to show that the model could be used to provide salinity estimates for different storm intensities on this part of the Mancos Shale. The potential influence of vegetation canopy cover on sediment production from these two sites was inferred by running RHEM with canopy cover values ranging from 0% to 100%. This changed sediment output by 111% to -91% relative to the present vegetation cover. Measures of the geometry of soil and vegetation patches at Dry-X, such as fractal dimension index and proximity index, showed a relationship to error residuals from RHEM. As the vegetation becomes less isolated, more uniform, and the tortuosity of the bare soil area increases, observed sediment decreases relative to RHEM predictions. The results of this study will help land management agencies assess the feasibility of mitigation strategies for reducing sediment and salinity loads from the saline and sodic soils of the Mancos Shale formation and indicate a possible benefit to incorporating the parameters that describe the spatial pattern of vegetation in RHEM.</p>

9 pp. / Principles of obtaining and interpreting utilization data on rangelands / Rangeland monitoring is essential for making sound management decisions. Monitoring requires repeated measurements of the same attributes over time. Perhaps the earliest and most widespread rangeland management monitoring data collection protocol was the development and establishment of the Parker 3-step Method on U. S. Forest Service rangelands, beginning in 1948. This method collected both objective and subjective data and provided a scoring technique for assessment purposes. This paper describes the development of the Method and suggests ways to summarize the ecological attributes collected on Parker transects, analyze the data and reinterpret them based on trends in plant species abundance, composition and soil cover.