Prescribed Fire Effects on Vegetation and Arthropod Dynamics, and Sampling Techniques in a Wyoming Big Sagebrush Community
Prescribed Fire Effects on Vegetation and Arthropod Dynamics, and Sampling Techniques in a Wyoming Big Sagebrush Community

Author: Edward C. Rhodes

Publisher:

Published: 2006

Total Pages: 258

ISBN-13:

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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 Redacted for privacy Redacted for privacy 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.

Wyoming Big Sagebrush Survival and Herbaceous Community Response to Prescribed Burns Across an Invasion Gradient of Annual Brome
Wyoming Big Sagebrush Survival and Herbaceous Community Response to Prescribed Burns Across an Invasion Gradient of Annual Brome

Author: Catherine Elizabeth Estep

Publisher:

Published: 2020

Total Pages: 98

ISBN-13:

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In many western rangeland ecosystems, fire is a natural disturbance to which native grasses and forbs are adapted, yet interestingly the dominant native shrub, Wyoming big sagebrush (Artemisia tridentata), is extremely sensitive to fire. Additionally, the role of fire is further confounded by potential interactions with invasive species. There is strong evidence that fires promote a positive feedback-loop enhancing annual brome (Bromus tectorum and B. arvensis) invasion in the sagebrush steppe and particularly the Intermountain West. However, evidence suggests that these mechanisms and processes may not be similarly expressed in the Great Plains. The Thunder Basin Ecoregion provides a unique opportunity to study how disturbances such as fire will affect diverse plant communities occurring near the edges of these two important regions. One recent study found that historical wildfires did not promote annual brome in the Thunder Basin Ecoregion, but these fires did almost completely eliminate sagebrush from the burned areas for many decades after fire. This research builds on previous results by mechanistically investigating the effects of prescribed burns across a range of fuel, fire behavior conditions, and annual brome abundance on the herbaceous community and Wyoming big sagebrush survival. In Chapter 1, I investigated how prescribed burns affect the herbaceous community relative to a gradient of annual brome abundance, fuel loading, and fire severities. In the first year following burn, fall burns reduced brome cover by 64% relative to unburned plots. Higher severity burns also dramatically reduced sagebrush densities as much as 98%, but when burn severity was low there was less of an impact. In Chapter 2, I assessed how fire behavior conditions affect Wyoming big sagebrush mortality and survival under a gradient of annual brome invasion, fuel loads, and fire behavior conditions. The basis for what we know about how fire affects sagebrush is primarily a function of large-scale assessments of wildfires, with very little quantification of the variability in fuels, fire weather, and fire temperatures. In this experiment, we determined what mechanisms are attributed to sagebrush survival. Models indicated that although fire weather and moisture were important predictors of shrub consumption, high preburn annual brome cover was the best predictor of individual sagebrush survival one year post fire.