Invasive species impose severe ecological and economic changes on their new ecosystems—the United States alone suffers billions of dollars’ worth of damage every year due to the introduction and proliferation of non-native species. Bioinvasions often are viewed as a problem to be tackled by a top-down central decisionmaker seeking to control invaders across large swaths of public land. In many regions around the world, however, bioinvaders spread, without regard to jurisdictional boundaries, over large landscapes that contain numerous, independently owned parcels of land, complicating control efforts.
In a new article in the American Journal of Agricultural Economics, “Individual and Cooperative Management of Invasive Species in Human-Mediated Landscapes,” my colleague James Wilen and I model the spread of invasive species and their spatial-dynamic externalities to explore how and when bottom-up coordinated control among independent landowners might achieve socially desirable levels of invasion control. How expansive would such cooperative management agreements need to be, and under what economic and invasion conditions are they likely to be most effective?
In a laissez-faire scenario involving multiple private property parcels, owners tend to under-control bioinvasions relative to what is best for society or their community. This happens because landowners generally only consider the damages that they will incur personally from the invasion when deciding what control measures to take. Each landowner’s control choice, however, affects not only the invasion and damages on his own property, but also the likelihood of spread and ease of control on neighboring properties. For example, early in an invasion—when its extent is limited to one or a few parcels of land—complete eradication of the invasion might be achieved through control on only a limited number of parcels, but this control effort would provide benefits to all landowners whose parcels eventually would have been affected by the invasion as it spread. If landowners only consider the benefits of invasion control for their own cattle’s forage or the health of their own trees, then control may not be in a landowner’s own best interest when the costs are sufficiently high. In this case, the wider landscape benefits of control would not be realized—resulting in externalities from invasion spread across landowners’ properties.
What if the external benefits of invasion control could be internalized through cooperative invasion control agreements? For example, a landowner not yet affected by the invasion might opt to share the costs of eradication with his neighbor in order to avoid future damages. Or perhaps more expansive coordinated control agreements, including large groups of neighbors, could achieve successful bottom-up control of invasions?
We show in our article that while independent private control decisions indeed tend to under-control invasions relative to socially optimal levels, cooperation with even a modest geographical reach can provide large social benefits. In particular, we find that less expansive landowner cooperation is needed to control invasions when marginal control costs are relatively low compared to damages, which are conditions when successful control provides the greatest gains for otherwise similar invasions. In contrast, for invasions where control costs are high relative to damages, but control is still optimal at the landscape scale, a larger extent of cooperation is needed to achieve control and the payoffs are smaller due the higher relative costs.
Our findings suggest alternatives to the conventional top-down policies typically evaluated by economists for invasion control. Instead of designing institutions that impose controls over a landscape of (potentially reluctant) independent landowners, efforts could perhaps be spent on mechanisms that increase private action and facilitate cooperative action. Policy measures, such as control subsidies or increased education about control strategies, could help increase private control efforts. Institutions that facilitate communication and coordination among landowners and development of cooperative control agreements could enhance successful cooperation by reducing transaction costs. Coordinated outcomes also could be encouraged through targeted allocation of private control incentives, such as by requiring that the distribution of financial or technical assistance be contingent upon coordination of control efforts among groups of landowners. Given the substantial social gains that can be achieved through successful private and cooperative control, these approaches could provide important social benefits and should be a continued focus of invasive species research.