Targeted grazing to reduce fuels and fires – does a light utilization level have an effect?

Wyoming fire (photo by J.D. Scasta).
Wyoming fire (photo by J.D. Scasta).

Researchers from Arizona and New Mexico, including University of Wyoming alumni Leticia Varelas, recently published a paper testing the effect of targeted grazing on fuel load and fires in Arizona.  Low stress herding coupled with low-moisture blocks was applied in the Coronado National Forest in southern Arizona in grass and shrub dominated areas.  The sites had rocky and steep topography and the primary fuel target was Lehmann lovegrass (Eragrostis lehmanniana), an exotic warm-season perennial grass originally from Africa.  Grazing was applied in December and January in two different years.  Study sites were paired based on similarities and treated with targeted grazing or no grazing (control).  In the second year, sites were switched so each site served once as the grazed site and once as the control.  Red Angus cattle were used and consisted of 58 cow-calf pairs and 2 bulls and estimated stocking rates in the targeted grazing study sites averaged 1.5 AUM’s per acre based on estimates of the number of animals and proportion of time spent in the treated areas.  Total fuel load was measured by clipping all plant material in each site and stubble height was used to determine grazing utilization.  This grazing pressure resulted in a light level of utilization estimated at 26%.  Fuel loads, specifically fuel bed depth and live herbaceous fuel load, were used to run a fire behavior computer model in the program BehavePlus and determine how fire rate of spread and flame length compared between targeted grazed and un-grazed sites.  In the modeling, weather variables were held constant, including wind speeds and fuel moisture.  Compared to the un-grazed sites, targeted grazing treatments had higher fuel loads of grasses that serve as fuels for fires, even in the very rugged terrain.  Subsequently, targeted grazing reduced fire rate of spread by 60% and 50% in grass and grass/shrub models respectively.  Flame lengths were also reduced by targeted grazing to below critical thresholds and would be predicted to be 4.5 feet or less in height, even in extreme conditions in both fuel models.  The authors concluded that “Our results from the fire model suggest that targeted grazing could reduce the potential cost of fighting fires on both grasslands and grass/shrub habitats in conditions similar to our study sites, even though average utilization was 26% in target sites”.  Furthermore, grazing alters fuelbed continuity and the computer modeling assumes a continuous fuelbed.  Authors concluded, “In our study, a projected lower-severity fire would make future wildfires less expensive and dangerous to address and potentially increase the rate of recovery following burns”.

Check out the paper at:

http://www.sciencedirect.com/science/article/pii/S155074241500144X

[Bruegger, R. A., Varelas, L. A., Howery, L. D., Torell, L. A., Stephenson, M. B., & Bailey, D. W. (2016). Targeted Grazing in Southern Arizona: Using Cattle to Reduce Fine Fuel Loads. Rangeland Ecology & Management,69(1), 43-51.]