Hoyt, William H.
Reinsvold, Robert J.
University of Northern Colorado
Type of Resources
Place of Publication
University of Northern Colorado
Most vegetation communities are in some way impacted by humans. This dissertation is composed of a series of studies aimed at understanding how the shortgrass steppe in northeastern Colorado responds to human disturbance. Specifically, it addresses the impact of gravel mining on a riparian area of the shortgrass steppe and its response to reclamation efforts. In addition, the impact of cattle grazing on the shortgrass steppe was investigated using exclosures. Studies concerning competition of noxious weeds present at the reclamation site were also conducted, both in the field and greenhouse. Finally, a qualitative study was completed addressing how student understanding and perception of gravel mine reclamation changed after visiting a mine reclamation site. The reclamation study evaluated plant and soil composition of an aggregate mine site on the shortgrass steppe of northeastern Colorado to determine its status five years following active mining. This assessment was made by comparing the gravel mine site to minimally-impacted reference sites on the Pawnee National Grasslands. Community composition, soil characteristics and productivity were all significantly different for the mined site. In particular, soil phosphorus and soil potassium levels were lower. In addition, the gravel mine site had lower levels of below-ground biomass. The results indicate that reclamation efforts on the mined site have been successful in establishing ground cover composed of native grasses and establishing functionally similar species to the references sites. Planting more native forbs and adding phosphorus and potassium to the soil is recommended to bring the experimental site closer to the reference site conditions. Grazing effects on riparian areas of the shortgrass steppe were tested using a seasonal and a multi-year study. Species composition and functional composition were compared for areas exposed to grazing and areas released from grazing. Soil nutrient levels and biomass levels were also compared but only over one grazing season. Results from the single grazing season study showed areas exposed to grazing had less above-ground biomass and greater heterogeneity than non-grazed areas. The multi-year study showed that species composition differed between grazed and un-grazed areas from the onset but demonstrated similar dynamics for diversity and species composition. The data suggested other environmental factors, perhaps hail, had a greater impact on the system than grazing. Release from grazing caused the system to change more than continual grazing and resulted in increased species evenness. This study demonstrated variability of species composition from year to year on the shortgrass steppe and supported the concept that grazing has minimal impact in regions adapted to low levels of precipitation. The competition studies investigated the possibility of utilizing native functionally equivalent plants as a means to control the spread and dominance of noxious weeds. Greenhouse and field studies were conducted to investigate the impact plant functionality and nativeness have on competitive ability of the ubiquitous noxious species Bromus tectorum and Cirsium arvense. Results indicate that Vulpia octoflora may inhibit the growth of Bromus tectorum but has little impact on Cirsium arvense, and that Achillea millifolium var. lanulosa does not significantly impact the growth of these noxious weeds. In the field, increased graminoid cover predicted decreased performance of Cirsium arvense. Data support the current practice of planting native perennial grasses in reclamation sites is an effective control measure for containing Cirsium arvense on the shortgrass steppe and suggest that planting Vulpia octoflora may be useful in controlling Bromus tectorum. A case study utilizing interviews, drawings, and observations was conducted. The goal of this case study was to investigate understanding and perceptions of high school geology students toward aggregate mining prior to and after a visit to a gravel mine reclamation site. Five underlying themes emerged from the data: increased knowledge of the gravel mining and reclamation processes, vocalization of the importance of reclamation, increased understanding of the structural composition of a gravel mine reclamation site on the shortgrass steppe, decreased emphasis of an anthropocentric purpose of mine reclamation, and identification of the location of a specific reclamation site. These results elucidate the importance in place-based education for developing student understanding of science concepts and stewardship perspectives.
Pawnee National Grassland (Colo.)
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