SMALL-SCALE DISTURBANCE EFFECTS ON MICROTOPOGRAPHY AND PLANT RECOVERY IN A SHORTGRASS COMMUNITY (GRAZING).

摘要

My general objective was to evaluate effects of small-scale disturbances on development of microtopography and plant recovery dynamics in a shortgrass community. This general objective was addressed by conducting three field experiments. In the first experiment, I focused on effects of disturbance size and soil texture on development of microtopographic relief associated with plants of Bouteloua gracilis. In the second experiment, I tested the hypothesis that death of a B. gracilis plant has a different effect on plant recovery and community composition than the death of other plant species. Also, effects of grazing on plant recovery were evaluated. In the third experiment, I studied the importance of disturbance type, grazing, and soil texture to plant recovery after mortality of numerous B. gracilis plants.; In shortgrass communities, microtopographic relief is heterogeneous, likely as a result of small-scale redistribution of soil between bare soil openings and B. gracilis plants through time. In the first study, small-scale redistribution of soil was affected by soil texture, patchy plant cover, and erosion-deposition processes associated with small-scale disturbances. Results from the second study were consistent with the hypothesis that death of a B. gracilis plant has a different effect on plant community composition than the death of other plant species. The most significant effect of different species was on the open space available (gap size). A second result was that death of an individual plant resulted in no significant changes in gap colonization, plant density or species richness on either the gap or neighborhood unless adequate environmental conditions occurred. Less colonization on ungrazed plots than on grazed plots indicated that although grazing may not change competition for soil resources in shortgrass communities, grazing enhances opportunities for colonizers on small gaps. In the third study, mortality of numerous B. gracilis plants caused a significant change in plant composition. Presence or absence of B. gracilis influenced species density and richness. Another response of plant community to the removal of B. gracilis was the change on plant size by individuals on disturbed plots. Season of the year, soil texture, disturbance type, and grazing were important to species that dominated vegetation, leading to different communities on disturbed plots with different characteristics.