No description available.

No description available.

The invasive Chinese tallow tree (Sapium sebiferum) is difficult to control because of its large seed bank and ability to resprout from cut stumps. I performed laboratory and field experiments to evaluate the effectiveness of mulching live trees for restoring invaded prairies. Herbicide use was limited to manual application to cut stumps. I manipulated mulch depths and types in the field and measured soil temperatures beneath them. At depths of as little as 5 cm, Sapium mulch damped soil temperature fluctuations and reduced seedling emergence. Reduced seedling emergence was not the result of allelopathic compounds in Sapium mulch because other mulch types suppressed emergence similarly. Substantial regrowth of native vegetation occurred through the mulch. Independent manipulations of mulch depth and temperature fluctuations in a lab experiment confirmed that mulch suppressed seed germination indirectly via soil temperature effects. This prairie site can now be managed by mowing or burning.

No description available.

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> 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 (MHSc--Health Science) -- AUT University, 2008. / Includes bibliographical references. Also held in print (xv, 121 leaves : col. ill. ; 30 cm.) in the Archive at the City Campus (T 612.76 MON)

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