Prescribed fire effects on vegetation and arthropod dynamics, and sampling techniques in a Wyoming big sagebrush community

approved: Jonathan D. Bates John C. Buckhouse 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 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 ModifiedWhittaker 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 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 sties 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 ModifiedWhittaker design. © Copyright by Edward C. Rhodes October 23, 2006 All Rights Reserved Prescribed Fire Effects on Vegetation and Arthropod Dynamics, and Sampling Techniques in a Wyoming Big Sagebrush Community by Edward C. Rhodes A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of