Economic Modeling and the Management of Exotic Annual Bromus Species: Accounting for Ecosystem Dynamics, Ecological Thresholds, and Spatial Interdependencies

Abstract

This chapter describes how economic models can inform management of exotic annual Bromus species on rangelands in the Western United States. It surveys published studies that develop bio-economic models of the management of Bromus species and other exotic annual invasive grasses, focusing on the challenges of rep-resenting the complex dynamics of rangeland ecosystems within tractable models of economic decision-making. The discussion starts with elements that are common to most economic models of Bromus management, then turns to contributions from the literature that have developed bio-economic models that capture three salient features of Bromus invasion: the dynamics of Bromus invasion, ecological thresh-olds related to Bromus , and spatial interdependencies in biophysical and human systems. The chapter synthesizes insights gained from this literature for managing Bromus in the Western United States, including insights on where to direct Bromus management resources on the landscape to achieve the greatest benefi t given limited funds for management and on how to improve the design of policies that encourage socially effi cient Bromus management by private land managers. The chapter con-cludes by identifying key areas where further research into the economics of Bromus management is needed. 15.1 Introduction Public and private land managers regularly make decisions that infl uence the preva-lence and spread of exotic annual Bromus species (Bromus hereafter) and other exotic annual invasive grasses on semiarid rangelands in the Western United States. Ranchers affect Bromus through weed control efforts and livestock management (inappropriate livestock grazing can reduce the ability of native plants to compete with Bromus). Public land management agencies affect Bromus through weed man-agement; post-wildfi re rehabilitation ; education, outreach, and incentive programs that target land managers; and regulation of the activities of ranchers and other pri-vate entities that operate on public land. Understanding how public and private land managers make decisions, and how their decisions are infl uenced by the fi nancial and ecological constraints they face, is essential for designing policies and regula-tions that encourage private managers to effectively manage Bromus invasions, as well as for determining the effi cient use of limited resources available to public agencies for Bromus management. This chapter surveys published economic studies that have developed and used integrated ecological a nd economic models (hence-forth, bio-economic models) to analyze public and private decision-making on semiarid rangelands affected by Bromus and other exotic annual invasive grasses and discusses the implications of these studies for the management of Bromus on rangelands in the Western United States. The chapter focuses on simulation and optimization bio-economic models that take into account one of three attributes of Bromus invasions that pose particular challenges to economic analysis: the temporal dynamics of invasion, ecological thresholds , and spatial interdependencies in biophysical and human systems . All these bio-economic models of Bromus grass management include an ecological component to represent how Bromus species behave and are likely to respond to management. A primary challenge when developing bio-economic models is to bal-ance the competing imperatives of (1) accurately representing the ecology of a Bromus invasion while (2) precisely and parsimoniously describing the elements of the economic decision problem. Ultimately, a modeler chooses which aspects of the complex ecology of Bromus invasion are necessary to include in the model—and what aspects can be safely ignored—to address a specifi c management or policy question . (For the studies reviewed in this chapter, the ecological complexity relates to the dynamics of Bromus invasion, including movements between stable ecologi-cal states separated by thresholds and to the spatial spread of Bromus .) Similarly, choices must be made about which aspects of the economic decision problem to include. As discussed in the next section, economic decision problems may include the decision-maker's objective function, constraints on the ability to meet the M. Eiswerth et al.