Year of Award

2017

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Resource Conservation

Department or School/College

Department of Ecosystem and Conservation Sciences

Committee Chair

Brady Allred

Commitee Members

Victoria Dreitz, Brian Martin

Keywords

fire-grazing interaction, mixed grass prairie, grazing distribution, forage production, vegetation heterogeneity, semiarid

Publisher

University of Montana

Subject Categories

Agricultural Science | Botany | Desert Ecology | Weed Science

Abstract

The fire-grazing interaction is well studied in mesic grasslands worldwide, but research is lacking in semiarid systems. In addition, the fire-grazing interaction reduces the invasion of exotic forage species in mesic grasslands by increasing the scale of grazing selection and may be a tool to control invasive plants in other grasslands. We examined the principal drivers and feedbacks of the fire-grazing interaction on the strength of cattle grazing selection, forage quantity and quality, and vegetation structure and composition in two pastures in northeast Montana at The Nature Conservancy’s Matador Ranch. We also determined the influence of time since fire, within the context of the fire-grazing interaction, on cover and herbicide efficacy of crested wheatgrass (Agropyron cristatum [L.] Gaertner), an introduced perennial grass with numerous negative impacts on grassland habitat. Cattle showed significant preference, use, and grazing utilization in recent burned patches that declined as time since fire increased. Cattle selection was driven by significantly increased forage quality in recent burns. Cattle established low forage quantity in recent burned patches, but the extent to which it was maintained varied with precipitation. Forage quality decreased with time since fire as forage quantity increased. Forage production returned to unburned levels after two years since fire, demonstrating that the mixed grass prairie is resilient to the fire-grazing interaction. Species composition was influenced primarily by site and year, though bare ground and litter were influenced by the fire-grazing interaction. The fire-grazing interaction shifted grazing preferences from being plant specific to patch specific in recent burns. The fire-grazing interaction maintained stable cover of A. cristatum in recent burned patches while it increased two fold elsewhere. Herbicide substantially reduced cover of A. cristatum regardless of years since fire, though plant mortality at the larger plot scale decreased with time since fire. The fire-grazing interaction alone may be a viable treatment option for small infestations of crested wheatgrass in native rangelands that utilizes the available forage base and reduces the economic and ecological costs of herbicide. In addition, the gradient of grazing utilization may enhance the effectiveness of cattle as ecosystem engineers of grassland habitat.

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© Copyright 2017 Jacob E. Powell