Submitted to: International Journal of Wildland Fire
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/7/2015
Publication Date: 6/4/2015
Citation: Davies, K.W., Boyd, C.S., Bates, J.D., Hulet, A. 2015. Dormant season grazing may decrease wildfire probability by increasing fuel moisture and reducing fuel amount and continuity. International Journal of Wildland Fire. 24(6):849-856. doi: 10.1071/WF14209.
Interpretive Summary: Wildfires are an ecological and economic risk for many semi-arid rangelands which has resulted in increased pressure for pre-suppression management of fuels. In rangelands, fuel management treatment options are limited by costs. We evaluated winter grazing as a tool to manage fuels in sagebrush rangelands because it can be applied at little cost. Winter grazing compared to no grazing decreased fine fuels and increased fuel moisture content without increasing exotic annuals or negatively impacting native plants. Winter grazing shortened the wildfire season from approximately three months to less than a month by increasing fuel moisture. The cumulative effect of winter grazing on fuels reduces wildfire risk and potential severity and thus has the potential to reduce wildfire suppression expenditures in rangelands.
Technical Abstract: 1. Wildfire is an ecological and economic risk for many semi-arid rangelands across the globe. This coupled with extreme wildfire seasons and mega-fires over the last decade have resulted in a call for more pre-suppression management actions. Dormant season grazing has been suggested as a treatment to reduce fuels in rangeland, but its effects on fuels has not been evaluated. There is also a risk that grazing may adversely affect native plants and promote exotic plant invasions. 2. We evaluated the influence of dormant season grazing (winter grazing in this ecosystem) by cattle on fuel cover, continuity, biomass, and moisture in Artemisia tridentata subsp. wyomingensis plant communities at five sites in southeastern Oregon, USA. Winter grazing was applied for four years prior to measurements and compared to ungrazed areas. 3. Winter grazing reduced fine fuel cover, continuity, height and biomass without increasing exotic annuals or negatively impacting native perennial bunchgrasses. 4. Winter grazing potentially shortens the wildfire season by increasing fuel moisture content. Fuel moisture in the winter grazed areas was high enough that burning was unlikely until the end of August; in contrast, the ungrazed areas were dry enough to burn in late June. 5. Fuel loading on perennial bunchgrasses was decreased 2.5-fold with winter grazing which reduces the potential for fire-induced mortality. 6. Synthesis and applications: Winter grazing’s cumulative effect from altering multiple fuel characteristics reduces wildfire risk and potential severity in A. t. subsp. wyomingensis communities. Most notably, winter grazing reduced the wildfire season from approximately three months to less than a month by increasing fine fuel moisture content. Dormant season grazing is likely an effective pre-suppression management action that can be applied across a diverse array of rangelands to decrease wildfire risk and reduce potential fire severity. Therefore, dormant season grazing has the potential to reduce wildfire suppression expenditures in many rangelands where fine fuel accumulation is an issue.