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WWRC 97-05hh
Effects of Herbivory on Willow (Salix spp.) Canopy Volume on Mountain Rangelands of Northern Wyoming


Grazing management of western riparian areas has become increasingly important. Willows, (Salix spp.) a common shrub species throughout the west are being used as an indicator of riparian condition. The structural diversity of a willow community provides important habitat for many species of wildlife. Willows are also a forage source for large ungulates. However, little is known about the effects of herbivory on willow and its structural diversity. Canopy volume can be used to quantify changes in community structure. This study investigated the relationship between willow canopy volume and utilization by large ungulates. Transects were randomly selected and established on two northern Wyoming grazing allotments to monitor canopy volume and utilization. Transects were evaluated seasonally, and before and after cattle use. Canopy volume was calculated using the height and diameter of each plant in an ellipsoid volume formula. Utilization measurements were calculated from the length of current years twig growth removed and the number of available twigs browsed. Regression analysis was used to define the relationship between changes in canopy volume and different levels of utilization at both the species and community level. New knowledge about canopy structure, and above ground responses to herbivory will provide valuable understanding of the ecological role of willow. These results will aid managers in determining proper use levels by large ungulates that will maintain willows as a wildlife habitat component.

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