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Author for correspondence: Jane M. Mangold, Land Resources and Environmental Sciences, Montana State University, P.O. Box 173102, Bozeman, MT 59717. (Email: [email protected])
Introduction
Invasions by exotic species have been cited as one of the leading causes of environmental change and decreases in biodiversity (Vitousek et al. 1996). Pimentel et al. (2005) estimated that nonindigenous species in the United States cause damages of $137 billion annually, with nonnative plants making up $34 billion of that cost. On rangelands, these economic impacts are associated with livestock production; in particular, noxious weeds reduce yield and quality of forage and can poison livestock (DiTomaso 2000). In addition, landowners incur expenses when they implement noxious weed management strategies aimed at limiting weed invasions or managing current infestations (Olson 1999). Overall, reductions in rangeland carrying capacity for livestock and increases in operating and management costs lead to reduced land value (Olson 1999).
Using livestock producer survey data and empirical weed impact data, we estimated the direct economic impacts of noxious weeds on privately owned rangeland in Montana. We estimated the average economic loss, including both the costs of control and lost forage to be $3.54 ha−1 yr−1, or $7,243 annually, for the average grazing unit in Montana (i.e., 2,046 ha [5,055 ac]). These costs are likely a lower bound on true costs, because we considered only direct costs; indirect costs, such as reduced economic activity associated with lower livestock production–based revenue, have often been included in other noxious weed economic impact assessments. The most commonly reported noxious weeds were Canada thistle [Cirsium arvense (L.) Scop.], leafy spurge (Euphorbia esula L.), and houndstongue (Cynoglossum officinale L.), while E. esula, C. arvense, and both spotted and diffuse knapweed (Centaurea stoebe L. and Centaurea diffusa Lam.) were reported as causing the largest decreases in livestock production. The top three strategies used to control established noxious weeds were chemical control, grazing, and biological control. Survey respondents estimated about 12% of their land is covered with noxious weeds, indicating noxious weeds are a common problem in Montana. Spending time and money on noxious weed management reduces household income, retail trade, and agricultural crop production, thus magnifying the direct economic impacts that we evaluated in...