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Open-File Report 20081214

U.S. GEOLOGICAL SURVEY
Open-File Report 20081214

Interactions Among Livestock Grazing, Vegetation Type, and Fire Behavior in the Murphy Wildland Fire Complex in Idaho and Nevada, July 2007

Prepared in cooperation with the Murphy Wildland Fire Grazing and Fuel Assessment Team

By Karen Launchbaugh, University of Idaho; Bob Brammer, Idaho Department of Lands; Matthew L. Brooks, U.S. Geological Survey; Stephen Bunting, University of Idaho; Patrick Clark, U.S. Department of Agriculture, Agricultural Research Service; Jay Davison, University of Nevada; Mark Fleming, Idaho Department of Fish and Game; Ron Kay, Idaho State Department of Agriculture; Mike Pellant, Bureau of Land Management; David A. Pyke, U.S. Geological Survey; and Bruce Wylie, ASRC Research and Technology Solutions contractor to U.S. Geological Survey

Abstract

A series of wildland fires were ignited by lightning in sagebrush and grassland communities near the Idaho-Nevada border southwest of Twin Falls, Idaho in July 2007. The fires burned for over two weeks and encompassed more than 650,000 acres. A team of scientists, habitat specialists, and land managers was called together by Tom Dyer, Idaho BLM State Director, to examine initial information from the Murphy Wildland Fire Complex in relation to plant communities and patterns of livestock grazing. Three approaches were used to examine this topic: (1) identify potential for livestock grazing to modify fuel loads and affect fire behavior using fire models applied to various vegetation types, fuel loads, and fire conditions; (2) compare levels of fuel consumed within and among major vegetation types; and (3) examine several observed lines of difference and discontinuity in fuel consumed to determine what factors created these contrasts.

The team found that much of the Murphy Wildland Fire Complex burned under extreme fuel and weather conditions that likely overshadowed livestock grazing as a factor influencing fire extent and fuel consumption in many areas where these fires burned. Differences and abrupt contrast lines in the level of fuels consumed were affected mostly by the plant communities that existed on a site before fire. A few abrupt contrasts in burn severity coincided with apparent differences in grazing patterns of livestock, observed as fence-line contrasts. Fire modeling revealed that grazing in grassland vegetation can reduce surface rate of spread and fire-line intensity to a greater extent than in shrubland types. Under extreme fire conditions (low fuel moisture, high temperatures, and gusty winds), grazing applied at moderate utilization levels has limited or negligible effects on fire behavior. However, when weather and fuel-moisture conditions are less extreme, grazing may reduce the rate of spread and intensity of fires allowing for patchy burns with low levels of fuel consumption.

The team suggested that targeted grazing to accomplish fuel objectives holds promise but requires detailed planning that includes clearly defined goals for fuel modification and appropriate monitoring to assess effectiveness. It was recommended that a pilot plan be devised to strategically place grazed blocks across a landscape to create fuel-reduction bands capable of influencing fire behavior. Also suggested was the development of a general technical report that highlights information and examples of how livestock grazing influences fire extent, severity, and intensity. Finally, the team encouraged continued research and monitoring of the effects of the Murphy Wildland Fire Complex. Much more can be learned from the effects of this extensive fire complex that may offer insight for future management decisions.

Contents

Abstract
Introduction and Background
Observations and Photographic Example of Fire Effects
Fire Behavior and Fuel-Consumption Analyses
Report Summary and Conclusions
References Cited
Appendix 1. Murphy Wildland Fire Grazing and Fuel Assessment Team
Appendix 2. Common and Scientific Names of Plants Referred to in Text. Scientific names follow the USDA PLANTS Database
Appendix 3. Glossary of Terms and Unit Abbreviations

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