Introduction

Invasive weeds are introduced plants that cause environmental or economic harm. Compared to native plants, these plants have greater net reproductive capacity and competitive ability for resources. They also lack natural controls that are absent in their new habitat. These traits and other aggressive abilities, such as fast growth, good dispersal, and tolerance of a wide range of environmental conditions, are associated with displacement of native plants and the native animals that rely on them. In addition to displacing native species, invasive weeds can irreversibly damage whole ecosystems and impact ecological services with serious economic consequences. The direct costs of invasive weeds include reduced grazing capacity and increased management expenses that increase the costs of producing livestock. The indirect costs of weeds include degradation of natural resources and wildlife habitat, which may be the basis of recreational and tourism revenues.

Invasive weeds infest over eight million acres in Montana. Most weed programs focus on land already infested with noxious weeds at a cost of about $20 per acre per year. This expenditure is justified because of the need to mitigate weeds and recover lands. But weeds continue to spread to new sites in spite of widespread control efforts. Most rangeland in Montana remains weed-free, but these ecosystems are threatened by likely invasion. Grasslands and riparian areas are susceptible to invasion because of frequent openings in plant cover where new weeds can establish. The protection of weed-free areas from invasion has been proven to be successful and cost-effective. Costly economic and ecological impacts can be prevented by prioritizing weed management in areas without weeds.

Cooperative prevention systems are needed to reduce the risks of invasion and environmental harm. Weed prevention areas meet this need by operating at the local level to reduce rangeland susceptibility to invasion, interrupt weed invasion pathways, and detect and eradicate new weeds using systematic monitoring approaches. Inventories direct management activity and establish ecological baselines to maintain over time. Proactive weed management strategies are site-specifically developed and collectively implemented by local rancher groups. Weed prevention areas take the approach that it is only a matter of time before weeds invade new areas. Ranchers and public land managers are anticipating invasion and taking a proactive role to keep weeds out, potentially saving millions of dollars in damages and control costs and preserving native plant and animal resources. The purpose of this publication is to describe the development and implementation of cooperative weed prevention areas in Montana and the coordinated efforts that protect rangelands from weed invasion.

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Last Modified: 08/02/2007