Ungulate grazing in sagebrush grassland: Mechanisms of resource competition
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Authors: N. T. Hobbs, D. L. Baker, G. D. Bear, and D. C. Bowden
Date: 1996
Journal: Ecological Applications
Volume: 6
Number: 1
Pages: 200-217
Summary of Methods: This study in Colorado examined the effects of variation in population density of Rocky Mountain elk (Cervus elaphus canadensis) on the availability and use of forage resources by cattle in a randomized complete block experiment conducted in sagebrush grassland during four years. The objective of the work reported in this study was to test the hypothesis that winter grazing by elk does not influence forage resources for cattle during the spring. The hypothesis was rejected: elk grazing exerted enhancing as well as harmful effects on forage available to cattle. In particular, elk grazing enhanced the nutritional quality of forage available to cattle by increasing live to dead ratios of standing crops. However, these improvements were not sufficient to overcome the harmful effects of elk grazing on forage availability. Reductions in supplies of forage available to cattle appeared to cause declines in their daily intake of dry matter and digestible energy. In the system studied, harmful impacts of elk grazing on cattle dry matter and energy intake began to occur when herbaceous forage available to cattle after elk grazing fell below about 45 g/m2 of dry matter. When forage production is low and cattle density is high, competition is a much stronger force than facilitation.
Article Summary / Main Points: None
Vegetation Types:
MLRA Ecoregions:
Agrovoc Control Words: Riparian zones Rangelands Wildlife
Article Review Type: Refereed
Article Type: Experimental Research
Keywords: cattle, competition, diet quality, diet selection, elk, facilitation, forage quality, functional response, grazing, net primary production, ungulates
Annotation: They manipulated elk numbers to achieve four levels of population density (0, 9, 15, and 31 elk/km2), replicated each level three times, and observed responses of vegetation and cattle to these manipulations. Elk were on pastures from December 27 to April 15. Stocking rates of cattle were chosen to achieve about 50% removal of the net annual aboveground production of perennial grasses in the control pastures. Pastures were stocked with cattle for 6 weeks during years 1 and 2 (May 8-June 18, 1987 and May 12-June 21, 1988), for 3 weeks during year 3 (May 10-May 31, 1989); and for 5 weeks during year 4 (May 9-June 13, 1990). Aboveground herbaceous biomass was harvested from each plot on May 1, June 1, and July 1 of each year. Plots were clipped to stubble height (1-cm) and sorted in the field.
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