Herbivory on shoalgrass by wintering redheads in Texas
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Authors: C. A. Mitchell, T. W. Custer, and P. J. Zwank
Date: 1994
Journal: Journal of Wildlife Management
Volume: 58
Number: 1
Pages: 131-141
Summary of Methods: The effect of redhead (Aythya Americana) grazing on shoalgrass (Halodule wrightii) habitat, of the Laguna Madre hypersaline lagoon along the Texas and Mexico coast, was investigated. Vegetation was collected monthly at 34 sites (including 7 exclosures) from mid-October to mid-March. Total biomass was measured in August. Three salinity measurements were recorded at each site. Soil samples were collected from October to February to determine total soil nitrogen, magnesium, potassium, and phosphorus levels. Moisture content and crude protein levels in rhizomes were also measured.
Article Summary / Main Points: Redhead grazing did not affect root biomass, but decreased the number of ramets and rhizome biomass in shoalgrass habitat, especially in heavily grazed areas. At heavily grazed sites, rhizome biomass decline, up to 23.7% per month, was greater than ungrazed or lightly grazed sites. All grazed sites had a 75% loss of rhizome biomass over winter. Root:rhizome ratio was more than twice as high on heavily grazed sites as ungrazed sites. Root biomass, rhizome moisture content and width, soil magnesium, phosphorous, and potassium were not affected by grazing. Nitrogen levels increased on grazed sites due to fecal deposition. About half of grazed sites recovered (biomass of 50.18 g dry mass/core) from goose grazing by the following winter, however, sites that were heavily grazed beyond a minimum threshold of rhizome biomass required more than one season for recovery. Redhead grazed areas within the lower Laguna Madre had lower salinities than ungrazed areas.
Vegetation Types: Riparian and Wetlands
MLRA Ecoregions: 150B Gulf Coast Saline Prairies 83E Sandsheet Prairie
Agrovoc Control Words: Riparian zones Grazing Wildlife
Article Review Type: Refereed
Article Type: Experimental Research
Keywords: redhead, aythya americana, shoalgrass, halodule wrightii, laguna madre, texas, herbivory
Annotation: This replicated study conducted over one year and its associated results are Applicatble to seagrass or hypersaline areas which are removed by grazing. As is true for all grazing research, the results are most directly applicable to areas with similar landscapes, species, level and season of use, and weather conditions. These results are useful in understanding the effect of heavy grazing on rhizome biomass reduction, increase in rhizomes nitrogen content, and lowering salinity.
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