Designing Optimal Strategies for Surveillance and Control of Invasive Forest Pests

This thesis focuses on the theme of detecting and managing invasive forest pests. Chapter 1 opens the dissertation with a review of relevant literature. In Chapter 2, we model optimal detection of sub-populations of invasive species that establish ahead of an advancing front. For many invaders, eradication of the main population is an untenable goal. However, it may be possible to treat and eradicate smaller sub-populations upon detection. Increasing detection effort is costly, yet leads to earlier detection of smaller populations. The level of detection effort that optimally balances this tradeoff depends, in part, on the distance from the main front: locations closer to the front with shorter management horizons enjoy lower reductions in overall cost from intervention. We find that the uninfested landscape is divided into two zones, characterized by different dynamically optimal management plans: a suppression zone and an eradication zone. In the suppression zone, optimal detection effort increases with distance from the front. At the distance where the suppression zone yields to the eradication zone, optimal detection effort plateaus at its maximum level.;In Chapter 3, we develop a model of optimal surveillance and control of forest pathogens and apply it to the case of oak wilt in a region within Anoka County, Minnesota. Managers allocate limited budgets between surveillance and control activities. Furthermore, they try to determine the locations where these efforts will have the most benefit. Our model allows for a heterogeneous landscape, where grid cells are differentiated by the number of trees and the number of infected trees. We develop a cost curve associated with the expected fraction of healthy trees saved from becoming infected. We find that the cost curve of saving healthy trees from infection is upward sloping, and that marginal cost increases along with the increase in the desired fraction of healthy trees. We also explore characteristics of sites selected for surveillance. In particular, we examine the characteristics of sites that make them high-priority sites for surveillance when the budget level is relatively low. We find that the best surveillance strategy is to prioritize sites with relatively low expected unit surveillance cost per tree saved from infection. Our results offer practical guidance to managers in charge of deciding how and where to spend limited public dollars when the goal is to reduce the number of trees newly infected by oak wilt.;Invasive species are major factors damaging forests on private lands. In the fourth chapter, we consider a situation where private lands are at risk of being infested by an invasive species. In Chapter 4, we model a private landowners' forest protection problem, in which each landowner decides among three possible strategies: prevention, monitoring and treatment, and no treatment. Landowners are differentiated by how much they value the forest on their property. Landowners do not know whether or not their forest will become infested, nor do they know whether monitoring will find an infestation if present: these events are probabilistic. We examine the change in the proportions of the population choosing these three treatments in both the landowners' equilibrium and the full information social optimum as the accuracy of monitoring changes. We find that the proportion of landowners taking preventive and no action increases as the accuracy of monitoring decreases; monitoring ceases to be chosen when monitoring accuracy declines below a threshold value. We also investigate the possible effects of a policy that raises the accuracy of monitoring on social welfare in both the landowners' equilibrium and the full information social optimum. We find that the policy closes the gap in social welfare between the landowners' equilibrium and the full information social optimum. However, it decreases social welfare in the full information social optimum. This finding casts doubt on whether improving the accuracy of monitoring is worth pursuing. Chapter 5 closes the thesis by summarizing the studies and discussing future extensions.