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Property Boundaries Affect Invasive Species Control


NSF-funded researchers at the University of California, Davis, have found that land divisions with multiple land managers can negatively impact the control of invasive species. This reduces the economic and ecological value of both public lands and private holdings in areas with a complex mosaic of ownership.

UC Davis graduate students Rebecca Niell, Clare Aslan, Matthew Hufford, Jeff Port, Jason Sexton, and Tim Waring, and faculty member James Wilen used a bioeconomic model and interviews to examine how land divisions and multiple land managers affect control of invasive species, using yellow star thistle in California rangelands as exemplar system.

In the model, they examined invasion outcomes of a landscape divided among multiple managers, assuming constant marginal damages and increasing marginal costs of control. Without control, invasion spreads on linear strip of land at a constant speed. Managers in the model choose control effort to minimize the sum of costs and damages over time. In addition, the researchers interviewed 40 ranchers about weed control and the effect of spread from neighboring lands.

The researchers found that land divisions hinder invasive species control by reducing managers’ incentives to control. Control efforts are more expensive if neighbors elect to not control because this provides a source for re-invasion. In interviews, 73% of ranchers said spread across property boundaries directly and negatively affects them. One rancher commented, “If [my neighbors] don’t control it, there’s no hope for me to. And I usually don’t try to fight it. I can’t afford to do that year after year after year with them not doing anything about their property.”

The researchers also found that cooperation among managers can improve success of regional invasive species management. Coordinated control on neighboring lands reduces the likelihood of re-invasion, making control efforts less costly and more successful. Specifically, 68% of interviewed ranchers explicitly stated the need for a coordinated control effort in order for an individual’s control efforts to be successful. In fact, some ranchers responded by controlling the source on the neighboring land or working out a cooperative control strategy with their neighbors. Further, managers affected later in an invasion benefit from the control efforts of managers early in an invasion. This provides incentive for early control of weeds.

Support from the US National Science Foundation Integrative Graduate Education and Traineeship program and US Department of Agriculture’s Environmental Research Service made this research possible.

Address Goals

In many parts of the western US, rangelands consist of a patchwork of privately owned ranges of varying size, federally managed lands, and state and local holdings. Weed control on such a mosaic depends critically upon cooperation between a diverse and uncoordinated group of land managers. This research combined an economic model with interviews of ranchers directly impacted by weed control. It allowed comparison of theoretical predictions with common practice and yielded insights into the challenges of weed control in areas partitioned by land divisions. Further, the results have provided local, state, and federal land managers with guidelines for working with private landowners to develop regional strategies for weed control.