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The effects of cattle grazing on Texas coastal salt marsh plants and birds
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Cattle grazing effects on plants and birds were examined in Spartina alterniflora-dominated marsh and adjacent Sporobolus virginicus-dominated hummocks within high tidal flats on Galveston Island, Texas. Grazed and ungrazed treatments were established April-June 1998. Vegetation data were taken within three elevation zones (low, middle, high) of Spartina alterniflora-dominated marsh, then analyzed by elevation zone with a two-factor (grazing treatment, site) ANOVA. Vegetation measurements included cover and height of each species present in 0.5 m² quadrats in June, August and December 1998; biomass measured April-May 1999; marsh/tidal flat boundary vegetation changes; and marsh edge erosion (change in location over time). The short time between the establishment of grazing treatments and sampling did not allow for conclusive cover and height changes. Ungrazed marsh total biomass and Spartina alterniflora biomass were greater at all elevations; Salicornia spp. biomass was greatest in the middle elevation grazed marsh, where trampling may allow higher marsh plants to colonize lower marsh habitats. The ungrazed marsh/tidal flat boundary had greater cover and height on the vegetated side, with no cover or height difference on the un-vegetated side. Marsh edge erosion was greater for the grazed marsh. Birds were sampled in Spartina alterniflora-dominated marsh at five elevation zones (low, middle, high, tidal flats, aerial feeding) by 10-minute point counts June-December 1998, with data analyzed by a three-factor (grazing treatment, elevation, date) ANOVA. The number of shorebirds, herons and egrets was greater in grazed treatments, with no difference found in the number of gulls, terns, sparrows, rails or other species. Bird diversity for the combined elevations and high marsh was greater in grazed treatments, with other elevations showing no difference. Vegetation measurements taken for the Sporobolus virginicus-dominated hummocks were analyzed by a two-factor (grazing treatment, site) ANOVA and included cover and height of each species present in 0.5 m² quadrats in August and December 1998, and hummock/high tidal flat boundary vegetation differences. Grazed hummocks had reduced total cover and height, and Sporobolus virginicus cover and height. There were no vegetation differences at the hummock/high tidal flat boundary.
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Includes bibliographical references (leaves 88-92).
Issued also on microfiche from Lange Micrographics.
Yeargan, Catherine A (2001). The effects of cattle grazing on Texas coastal salt marsh plants and birds. Master's thesis, Texas A&M University. Available electronically from
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