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United States Department of Agriculture

Agricultural Research Service

Title: Effect of Sheep Grazing and Fire on Sage Grouse Populations in Southeastern Idaho

Authors
item Pedersen, E - TEXAS A&M UNIV
item Connelly, J - IDAHO DPT OF FISH & GAME
item Hendrickson, John
item Grant, W - TEXAS A&M UNIV

Submitted to: Ecological Modelling
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 26, 2002
Publication Date: July 1, 2003
Citation: PEDERSEN, E.K., CONNELLY, J.W., HENDRICKSON, J.R., GRANT, W.E. EFFECT OF SHEEP GRAZING AND FIRE ON SAGE GROUSE POPULATIONS IN SOUTHEASTERN IDAHO. ECOLOGICAL MODELLING 165:23-47. 2003.

Interpretive Summary: This paper describes a computer model that predicts the effect of grazing and fire on sagebrush community vegetation and sage grouse population dynamics. Model predictions correspond well with long-term observations of changes in sagebrush canopy cover following fire and with field data on seasonal dynamics of the grass growth. Model predictions also correspond well with field observations of changes in sage grouse population size related to changes in sagebrush canopy cover. Model predictions suggest that large fires occurring at high frequencies may lead to the extinction of sage grouse populations, whereas fires occurring at low frequencies may benefit sage grouse if burned areas are small and sheep grazing is absent. Sheep grazing may contribute to sage grouse population decline, but is unlikely to cause extinction under fire regimes favorable to sage grouse.

Technical Abstract: This paper describes the development, evaluation, and use of a model that simulates the effect of grazing and fire on temporal and spatial aspects of sagebrush community vegetation and sage grouse population dynamics. The model is represented mathematically as a discrete-time, stochastic compartment model based on difference equations with a time interval of 1 week. In the model, sheep graze through sage grouse breeding habitat during spring and fall, and different portions of the area can burn at different frequencies, creating a habitat mosaic of burned and unburned areas. The model was evaluated by examining predictions of (1) growth of sagebrush canopy cover after fire, (2) seasonal dynamics of grass and forb biomass under historical environmental conditions, and (3) sage grouse population dynamics associated with selected sagebrush canopy covers. Simulated changes in sagebrush canopy cover following fire correspond well with qualitative reports of long-term trends, simulated seasonal dynamics of herbaceous biomass correspond well with field data, and simulated responses of sage grouse population size and age structure to changing sagebrush canopy cover correspond well to qualitative field observations. Simulation results suggest that large fires occurring at high frequencies may lead to the extinction of sage grouse populations, whereas fires occurring at low frequencies may benefit sage grouse if burned areas are small and sheep grazing is absent. Sheep grazing may contribute to sage grouse population decline, but is unlikely to cause extinction under fire regimes that are favorable to sage grouse.

Last Modified: 7/31/2014
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