A predictive understanding of plant community response to various environmental influences (e.g. type, timing and frequency of disturbance, site productivity, fertilization, etc.) is a general goal of plant ecology. This study sought to further understanding of mesic grassland dynamics in KwaZulu-Natal using long-term field experiments (> 50 years) and short-term pot and plot competition experiments. The specific objectives were to: 1) examine the effects of long-term burning of grassland on soil organic matter content because of its potential impact on nitrogen cycling and community composition, 2) examine patterns of community composition and species richness in response to different type, timing and frequency of disturbance (burning and mowing) in a long-term grassland burning and mowing experiment and to different type and amounts of fertilizer application in a long-term grassland fertilization experiment, 3) develop hypotheses concerning the response of different species to disturbance and fertilization, and test these hypotheses using pot and plot competition experiments, and 4) provide a general synthesis of the results of the various field, pot and plot experiments that may be used to develop a predictive theoretical framework for mesic grassland dynamics. Total soil nitrogen was lowest in sites burnt annually, intermediate in sites burnt triennially and highest in sites protected from disturbance and sites mown annually in the dormant-period (spring or winter). Winter burning reduced soil organic carbon and total soil nitrogen more than spring burning. Mineralizable nitrogen was reduced by burning. The different effects of type, timing and frequency of disturbance on total soil nitrogen appeared to be an important determinant of community composition and species richness. Short-grass species (Themeda triandra, Eragrostis capensis, Heteropogon contortus, Diheteropogon amplectens and Eragrostis racemosa) were most abundant in annually burnt sites (especially winter burnt sites), whereas medium and tall-grass species (Eragrostis curvula, Cymbopogon spp., Hyparrhenia hirta and Aristida junciformis) were most abundant in triennially burnt sites, sites protected from disturbance and sites mown annually in the dormant-period, all of which had higher total soil nitrogen than annually or biennially burnt sites. Species richness and short-grass species declined with increasing levels of nitrogen fertilization in the fertilizer experiment and declined with increasing productivity and nitrogen availability in both the fertilizer and burning and mowing experiments. Thus, it was hypothesized that the type, timing and frequency of disturbance resulted in different compositional states through different effects on soil resources (especially nitrogen), which affected the competitive balance between short and tall species. The hypothesis that composition was determined by disturbance-mediated soil nitrogen availability was supported by competition experiments, which revealed that shortgrass species were most competitive in low-nutrient/low-productivity treatments and tall-grass species most competitive in high-nutrient/high-productivity treatments. The fertilizer experiment and a competition experiment revealed that tall broad-leaved species were most competitive in sites of highest productivity, fertilized with both nitrogen and phosphorus, whereas tall narrow-leaved species were most competitive in sites of intermediate productivity, fertilized with nitrogen only. It was hypothesized that summer mowing increased the abundance of short-grass species and decreased the abundance of tall-grass species in the burning and mowing experiment by increasing the competitive ability of short-grass relative to tall-grass species, rather than the tall-grass species being less tolerant of mowing. A competition experiment revealed that tall-grass species (Hyparrhenia hirta and Panicum maximum) were as tolerant of cutting as a short-grass species (Themeda triandra). Themeda triandra was shown to become extremely competitive in cutting treatments, reducing the biomass of most other species relative to their monoculture biomass, showing that its dominance of mown sites in the burning and mowing experiment was a result of its superior competitive ability rather than greater tolerance of mowing. However, many tall erect herbaceous dicots appeared to be intolerant of summer mowing, probably because their meristems are aerial and easily removed by mowing, whereas short creeping herbaceous dicots were increased by summer mowing probably because their meristems were below the mowing height. Further, these short species would be vulnerable to shading in unmown sites. Thus, species with basal meristems (hemicryptophytes) or meristems near the soil surface (geophytes) appear to be more tolerant of mowing than species with aerial meristems (phanerophytes), but the tradeoff is that a low meristem height renders them vulnerable to shading in unmown sites. Very high litter accumulation in the sites protected from disturbance appeared to have a direct influence on community composition and species richness. Species that dominated these sites (e.g. Tristachya leucothrix & Aristida junciformis) initiated tillers below-ground and had sharp erect shoots that appeared to be an adaptation for penetrating litter. Species that initiate tillers below-ground are probably less vulnerable to the effects of shading by litter because their tiller initiation is not dependent on high light availability. The fact that Aristida junciformis was shown to have very low competitive ability in two competition experiments, suggests its dominance of protected sites was through tolerance of high litter levels rather than competitive exclusion of other species. Low grass species richness in these sites was probably a result of an inability of many species to tolerate these high litter levels. This study has revealed that inherent site productivity and its interaction with the effect of disturbance on soil resources and litter levels is a major determinant of community composition and species richness. The effect of type, timing and frequency of disturbance on soil nitrogen was able to account for the principal changes in community composition. Thus, the influence of disturbance on soil nitrogen is a unifying principle in plant ecological theory that enables greater understanding of disturbance-composition relationships. However, intolerance of certain forms of disturbance (e.g. mowing) by species with aerial meristems, or intolerance of accumulating litter in the absence of disturbance by species without sharp erect shoots, may also have important influences on composition. In addition, this study has revealed that plant traits (height, leaf width, position of tiller initiation, shoot morphology and position of meristems) were well correlated with the various effects of disturbance and fertilization on community composition, indicating that a plant trait-productivity-disturbance framework has great potential for understanding and predicting species response to disturbance and multiple limiting nutrients. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2003.

Fire has been an important influence on the structure and health of the North American grasslands for hundreds of years. In Jersey County Illinois, two natural loess hill prairies were studied to compare the effectiveness of varying management regimes. The purpose was to determine how a burn vs. a nonburn management regime enhances or hinders the establishment of the prairie grasses and forbs in a tallgrass hill prairie ecosystem. The variables studied included: the vegetational abundance, the frequency, and the biomass of the species that were present. In addition the soil's organic matter content and pH were measured. Overall, the Fire Road Prairie, or the unburned prairie, proved to be the community that was deteriorating and becoming unproductive. Whereas, the Osage Prairie contained a balance of grasses and forbs that were representative of a healthy and thriving community. The data supported the existing theory that a burn management plan does help the overall stability and productivity of a tallgrass ecosystem. / Department of Natural Resources and Environmental Management

A stratified sampling method was used to study the effects of two prescribed fires on a 250-acre section at the northwest end of Fork Ridge, Hoosier National Forest, in the spring of 1993 and 1995. An unburned area at the southeast end of Fork Ridge, adjacent to the burned area, and with similar forest communities, was used as a control area. Three growing seasons after the last fire, the burned area exhibited noticeable differences in understory vegetation. Herbaceous species diversity and richness, total herb cover on mesic sites, and mean percent cover and relative frequency for mesic-site, shade-tolerant species were greater on the burned area than on the unburned area. Dry-site, shade-intolerant tree seedlings including scarlet oak (Quercus Coccina), chestnut oak (Quercus prinus), sassafras (Sassafras albi dum), and tulip poplar (Liriodendron tulipifera) had higher relative frequency in the burned area, while shade-tolerant flowering dogwood (Cornus Florida) had lower relative frequency. / Department of Biology

During autumn 1993, the U. S. Forest Service began implementing a program of prescribed surface fire in the Fork Ridge region of Hoosier National Forest. To determine the effects of the prescribed surface fire on ground- and shrub-nesting nearctic migrants, I conducted vegetation structure sampling, bird abundance surveys, and nest searches during the 1996 and 1997 breeding seasons. The prescribed surface fire drastically reduced understory vegetative cover from 0.0 to 2.5 m above ground and the density of live stems < 5.0 cm dbh. Herbaceous cover < 0.5 m tall in the burned site returned to levels similar to the unburned site within 2 years of the burn.Prescribed burning had little effect on overall avian species diversity, but altered the community composition. In 1996, there were 12 species present in the unburned site which were absent in the burned site and 9 species present in the burned site which were absent in the unburned site. In 1997, there were 9 species present in the unburned site which were absent in the burned site and 7 species present in the burned site which were absent in the unburned site. As a guild, ground- and shrub-nesting nearctic migrants and residents were less abundant in the burned site compared to the unburned site. Conversely, species such as Indigo Buntings (Passerina cyanea) and White-breasted Nuthatches (Sitter carolinensis) were more abundant in the burned site.Nests in the burned site had a 25% success rate, whereas nests in the unburned site had a 44% success rate. Nest parasitism did not differ between the burned site (1.2 cowbird eggs/nest) and unburned site (0.9 cowbird eggs/nest). Worm-eating Warblers (Helmitheros vermivorus) were the only ground- and shrunb-nesting nearctic migrant found in the burned site. Worm-eating Warbler nests in the burned site were characterized as having greater understory cover than surrounding burned areas. My results suggest that prescribed surface fires in Fork Ridge may be negatively impacting some ground- and shrub-nesting migrants by altering nesting habitat. / Department of Biology

No abstract available. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1983.

Prescribed burning is an important management tool for the restoration and maintenance of tallgrass prairies. To improve fire behaviour prediction in tallgrass prairies, I assessed three different aspects of fire behaviour - heat of combustion, fuel load and rate of spread. Heat of combustion was found to vary amongst certain tallgrass species but the relatively small differences in means is unlikely to contribute significantly to fire behaviour. Average fuel loads in Ontario tallgrass prairie sites were found to be higher than current default value used in fire behaviour prediction. Three rapid fuel load assessment techniques were tested. Finally, the predictions of three fire behaviour prediction systems - the FBP System, BehavePlus and an Australian grassfire spread model, were compared with actual fire behaviour observations. The FBP System was found to perform poorly while both BehavePlus and the Australian model exhibited relatively strong relationships between observed and predicted rates of spread.

Prescribed burning is an important management tool for the restoration and maintenance of tallgrass prairies. To improve fire behaviour prediction in tallgrass prairies, I assessed three different aspects of fire behaviour - heat of combustion, fuel load and rate of spread. Heat of combustion was found to vary amongst certain tallgrass species but the relatively small differences in means is unlikely to contribute significantly to fire behaviour. Average fuel loads in Ontario tallgrass prairie sites were found to be higher than current default value used in fire behaviour prediction. Three rapid fuel load assessment techniques were tested. Finally, the predictions of three fire behaviour prediction systems - the FBP System, BehavePlus and an Australian grassfire spread model, were compared with actual fire behaviour observations. The FBP System was found to perform poorly while both BehavePlus and the Australian model exhibited relatively strong relationships between observed and predicted rates of spread.

Thesis (M.S.)--University of Nevada, Reno, 2005. / "August, 2005." Includes bibliographical references (leaves 110-117). Library also has microfilm. Ann Arbor, Mich. : ProQuest Information and Learning Company, [2005]. 1 microfilm reel ; 35 mm. Online version available on the World Wide Web.

Thesis (Ph.D.)--University of Western Sydney, 2007. / A thesis submitted to the University of Western Sydney, College of Health and Science, Centre for Plant and Food Science, in fulfilment of the requirements for the degree of Doctor of Philosophy. Includes bibliographical references.

Thesis (M.S.)--Montana State University--Bozeman, 2004. / Typescript. Chairperson, Graduate Committee: Clayton B. Marlow. Includes bibliographical references (p. 49-53).