Date of Award:

5-2009

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Wildland Resources

Committee Chair(s)

Christopher A. Call

Committee

Christopher A. Call

Committee

Michael J. Jenkins

Committee

Eugene W. Schupp

Committee

Roger E. Banner

Committee

Thomas A. Monaco

Abstract

Studies were conducted to determine the effectiveness of using targeted grazing and prescribed burning as tools to reduce fire hazards and cheatgrass (Bromus tectorum) dominance on rangelands in the northern Great Basin. A field study, with four grazing-burning treatments (graze and no-burn, graze and burn, no-graze and burn, and no-graze and no-burn), was conducted on a B. tectorum-dominated site near McDermitt, Nevada from 2005-2007. Cattle removed 80-90% of standing biomass in grazed plots in May 2005 and 2006 when B. tectorum was in the boot (phenological) stage. Grazed and ungrazed plots were burned in October 2005 and 2006. Targeted grazing in May 2005 reduced B. tectorum biomass and cover, which resulted in reductions in flame length and rate of spread when plots were burned in October 2005. When grazing treatments were repeated on the same plots in May 2006, B. tectorum biomass and cover were reduced to the point that fires did not carry in grazed plots in October 2006. Fuel characteristics of the October 2005 burns were used to parameterize dry climate grass models in BehavePlus 3.0, and simulation modeling indicated that grazing in spring (May) would reduce the potential for catastrophic fires during the peak fire season (July-August). The graze-and-burn treatment was more effective than grazing alone (graze and no-burn treatment) and burning alone (no-graze and burn treatment) in reducing B. tectorum cover, biomass, plant density, and seed density, and in shifting species composition from a community dominated by B. tectorum to one composed of a suite of species [including tumble mustard (Sisymbrium altissimum), clasping pepperweed (Lepidium perfoliatum), and Sandberg bluegrass (Poa secunda)], with B. tectorum as a component rather than a dominant.

A simulation study was designed to compare the cost-effectiveness of using cattle grazing and herbicide to create fuel breaks on B. tectorum-dominated landscapes in the northern Great Basin. Fuel characteristics from this targeted grazing study and from a Plateau® (Imazapic) herbicide study near Kuna, Idaho were used to parameterize fire behavior models and simulate flame lengths and rates of spread for the two fuel reduction treatments under peak fire conditions using BEHAVE Plus. Targeted grazing and Plateau® had similar reductions in flame length and rate of spread. Cattle grazing had high fixed costs (primarily fencing), and was more cost-effective than applications of Plateau® under five fuel loading scenarios except for three consecutive years of low fuel loads.

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