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