Abstract:
In the western United States, sagebrush (Artemisia spp L.) dominated
rangelands are extensive, accounting for approximately 63 million ha. The
Wyoming big sagebrush (Artemisia tridentata Nutt. ssp. wyomingensis Beetle &
Young) alliance is found in more xeric environments, occupying the largest area of
the big sagebrush complex in areas within a 200-300mm precipitation zone at
elevations ranging from 610-2130m.
Wyoming big sagebrush communities provide habitat for nearly 100 bird and
70 mammal species throughout its range. A species that is of particular concern is the
sage grouse (Centrocercus urophasianus Bonaparte), which depends on big
sagebrush associations for food, nesting and cover. Much of its historical range has
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dwindled, prompting increasing scrutiny on land use and management throughout the
big sagebrush association. Destruction of remaining habitat and the danger of
invasion by annual grasses such as cheatgrass (Bromus tectorum L.), has necessitated
the assessment of the effects of disturbance such as fire on these communities.
This study was designed to: (A) determine the effects of prescribed fire on
vegetation characteristics, (B) analyze the specific response of forbs and arthropods
that are important in the diet of sage grouse to fire, and (C) compare the Modified-
Whittaker and Daubenmire methods of estimating species richness and vegetation
cover in a Wyoming big sagebrush community.
In the first project, prescribed fire had little effect on herbaceous density,
cover, or species richness, but did increase perennial grass and total herbaceous
standing crop the second and third year post burn, and annual forb standing crop the
first and second year. Big sagebrush and total shrub cover and density were greatly
reduced in burned treatments. Green rabbitbrush cover was greater in unburned
treatments, but no change in density was noted. Burning did not affect soil water
availability.
The second project showed little overall benefit to perennial forbs preferred
by sage grouse, however there was a short-lived increase in Microsteris/Collinsia
parviflora (Lindl.) cover in the second post burn year. Prescribed fire may be
detrimental to Hymenoptera abundance. Orthoptera may benefit from prescribed
fire, but further exploration is needed in that area. Annual exotic species richness was not shown to increase in either sampling
method or treatment in the third project. This is important, as it shows that sites
which are dominated by a large proportion of native species from various functional
groups can resist invasion. There was no clear-cut delineation between the
Modified-Whittaker and Daubenmire methods. While there were some similarities
in the data between the two, the Modified-Whittaker method had substantially
different percent cover estimations for perennial grass and total herbaceous
components in 2005. The Modified-Whittaker method also did not detect treatment
effects for biotic crust, bare ground/rock, and litter cover measurements that were
seen with the Daubenmire method. Shrub cover measurements were similar in both
methods. Further investigation is warranted to test the applicability of the Modified-
Whittaker design.
