Simulating long-term effectiveness and efficiency of management scenarios for an invasive grass
AIMS Environmental Science
Resource managers are often faced with trade-offs in allocating limited resources to manage plant invasions. These decisions must often be made with uncertainty about the location of infestations, their rate of spread and effectiveness of management actions. Landscape level simulation tools such as state-and-transition simulation models (STSMs) can be used to evaluate the potential long term consequences of alternative management strategies and help identify those strategies that make efficient
... that make efficient use of resources. We analyzed alternative management scenarios for African buffelgrass (Pennisetum ciliare syn. Cenchrus ciliaris) at Ironwood Forest National Monument, Arizona using a spatially explicit STSM implemented in the Tool for Exploratory Landscape Scenario Analyses (TELSA). Buffelgrass is an invasive grass that is spreading rapidly in the Sonoran Desert, affecting multiple habitats and jurisdictions. This invasion is creating a novel fire risk and transforming natural ecosystems. The model used in this application incorporates buffelgrass dispersal and establishment and management actions and effectiveness including inventory, treatment and post-treatment maintenance. We simulated 11 alternative scenarios developed in consultation with buffelgrass managers and other stakeholders. The scenarios vary according to the total budget allocated for management and the allocation of that budget between different kinds of management actions. Scenario results suggest that to achieve an actual reduction and stabilization of buffelgrass populations, management unconstrained by fiscal restrictions and across all jurisdictions and private lands is required; without broad and aggressive management, buffelgrass populations are expected to increase over time. However, results also suggest that large upfront investments can achieve control results that require relatively minimal spending in the future. 428 Investing the necessary funds upfront to control the invasion results in the most efficient use of resources to achieve lowest invaded acreage in the long-term. Invasive species are a recognized problem, impacting native systems, human health, and economies. Management of invasive species is a high priority in many agencies, but limited funds often dictate that management is conducted without a rigorous, quantitative assessment of alternatives and without a clear long-term plan. Managing for invasive species is a complex decision problem which involves determining if control or mitigation are possible; determining the potential impacts of an invasion and the resources required for addressing the invasion; and determining which actions to spend limited resources on (e.g., control versus inventory), which control methods to use, and where and when to use them. These decisions are further complicated by exogenous management decisions made by neighboring land owners and managers whose decisions affect propagule sources . There are relatively few published studies that include a cost-benefit or multi-criteria analysis to aid decision making for management of biological invasions  . The majority of invasive species decision tools are focused on risk analysis (i.e., assessing the risk or impact of an invasion that has not yet occurred), or on the decision to try to eradicate, contain or control an existing invasion  . Many of these models examine the trade-offs in resource allocation between inventory efforts to locate a species and management efforts to eradicate or contain a species [e.g., 3,4,5]; and many attempt to model how to optimally control invasive species [e.g., 6,7]. Models considering the optimal control of invasive species require relatively reductionist management alternatives (e.g., do nothing, contain, or eradicate), and most of these studies have developed their own models rather than using existing frameworks. Thus, these types of models can have limited practical applications for managers who need to consider a more complicated set of management alternatives and who need to be able to interact with the decision tool to test assumptions and alternatives as new information is learned and as circumstances change. State and transition simulation modeling (STSM) offers a pre-existing framework and a standalone tool that can be used to integrate many of the important components of an invasion: habitat suitability, population dynamics, local dispersal and management activities. STSMs allow for a wide variety of management scenarios to be considered, including the ability to allow differing management strategies and effort levels across different land ownerships. STSM decision support tools can be used to simulate and explore how an invasion may progress over time, and how implementing a variety of potential management alternatives may affect long-term outcomes on the landscape. These simulations can point to important scientific uncertainties and can inform managers of how to most effectively and efficiently allocate scarce resources. Several examples of applications of STSM can be found in this special issue, ranging from modeling the ecosystem carbon implications of land use and land cover change across an entire state  to a climate sensitive retrospective and prospective model of whitebark pine in the Greater Yellowstone Ecosystem  .