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Products: Invasive Species

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The Good, Bad, and Ugly of Watershed Management

Efficient management of groundwater resource systems requires careful consideration of relationships — both positive and negative — with the surrounding environment. The removal of and protection against “bad” and "ugly" natural capital such as invasive plants and feral animals and the enhancement of “good” capital (e.g. protective fencing) are often viewed as distinct management problems. Yet environmental linkages to a common groundwater resource suggest that watershed management decisions should be informed by an integrated framework. We develop such a framework and derive principles that govern optimal investment in the management of two types of natural capital — those that increase recharge and those that decrease recharge — as well as groundwater extraction itself. Depending on the initial conditions of the system and the characteristics of each type of natural capital, it may make sense to remove bad capital exclusively, enhance good capital exclusively, or invest in both activities simultaneously until their marginal benefits are equal.


Optimal Joint Management of Interdependent Resources: Groundwater vs. Kiawe (Prosopis pallida)

Local and global changes continue to influence interactions between groundwater and terrestrial ecosystems. Changes in precipitation, surface water, and land cover can affect the water balance of a given watershed, and thus affect both the quantity and quality of freshwater entering the ground. Groundwater management frameworks often abstract from such interactions. However, in some cases, management instruments can be designed to target simultaneously both groundwater and an interdependent resource such as the invasive kiawe tree (Prosopis pallid), which has been shown to reduce groundwater levels. Results from a groundwater-kiawe management model suggest that at the optimum, the resource manager should be indifferent between conserving a unit of groundwater via tree removal or via reduced consumption. The model’s application to the Kona Coast (Hawai‘i) showed that kiawe management can generate a large net present value for groundwater users. Additional data will be needed to implement full optimization in the resource system.


Economic Analysis of the Proposed Rule to Prevent Arrival of New Genetic Strains of the Rust Fungus Puccinia psidii in Hawai‘i

Since its first documented introduction to Hawai‘i in 2005, the rust fungus P. psidii has already severely damaged Syzygium jambos (Indian rose apple) trees and the federallyendangered Eugenia koolauensis (nioi). Fortunately, the particular strain has yet to cause serious damage to ‘ōhi‘a, which comprises roughly 80% of the state’s native forests and covers 400,000 ha. Although the rust has affected less than 5% of Hawaii’s ‘ōhi‘a trees thus far, the introduction of more virulent strains and the genetic evolution of the current strain are still possible. Since the primary pathway of introduction is Myrtaceae plant material imported from outside the state, potential damage to ‘ohi‘a can be minimized by regulating those high-risk imports. We discuss the economic impact on the state’s florist, nursery, landscaping, and forest plantation industries of a proposed rule that would ban the import of non-seed Myrtaceae plant material and require a one-year quarantine of seeds. Our analysis suggests that the benefits to the forest plantation industry of a complete ban on non-seed material would likely outweigh the costs to other affected sectors, even without considering the reduction in risk to ‘ōhi‘a. Incorporating the value of ‘ōhi‘a protection would further increase the benefit-cost ratio in favor of an import ban.

Working Paper

Species Invasion as Catastrophe: The Case of the Brown Tree Snake


This paper develops a two-stage model for the optimal management of a potential invasive species. The arrival of an invasive species is modeled as an irreversible event with an uncertain arrival time. The model is solved in two stages, beginning with the post-invasion stage. Once the arrival occurs, the optimal path of species removal is that which minimizes the present value of damage and removal costs plus the expected present value of prevention costs. An expenditure-dependent, conditional hazard rate describing species arrival is developed based on discussions with natural resource managers. We solve for the optimal sequence of prevention expenditures, given the minimum invasion penalty as just described. For the case of the Brown Tree Snake potentially invading Hawaii, we find that pre-invasion expenditures on prevention are inverse U-shaped in the hazard rate. Efficient prevention should be approximately $2.9million today and held constant until invasion. Once invasion occurs, optimal prevention requires $3.1million annually and $1.6million per year on species removal to keep the population at its steady state level, due to high search costs at very small population levels.

Published: Burnett, K., S. Pongkijvorasin, and J. Roumasset. "Species Invasion as Catastrophe: The Case of the Brown Tree Snake," Environmental and Resource Economics, 51:241-254, doi:10.1007/s10640-011-9497-3.


An Economic Assessment of Biological Control for Miconia calvescens in Hawaii

Biocontrol, the introduction of organisms to control an unwanted species, has been cited as a powerful method to manage the invasive species Miconia calvescens in Hawaii. In addition to ecological advantages, biocontrol is often regarded as less costly than traditional methods despite the large initial investment. Currently, miconia in Hawaii is treated through aerial and manual operations, which cost over $1 million annually. Biocontrol for miconia in Hawaii began in 1997 and the search for more agents continues today. Although biocontrol for miconia has already begun, prior to this study no assessment of its economic justifiability had been done. This research evaluates the present value of net benefits of miconia biocontrol in Hawaii. Cost data were gathered from scientists in charge of biocontrol programs. Benefits were defined as the cost-savings of current control methods. Two different biocontrol programs were modeled: control achieved by a single agent, and control achieved by a suite of agents. In addition, different dispersal rates and efficacies of biocontrol and two release dates were modeled. Because most costs of biocontrol are incurred before the release of a successful agent and the benefits are only realized post-release, each scenario was evaluated over a 50-year time horizon. The results indicate a positive present value of net benefits in all scenarios, ranging from $12.8 million to $36.1 million. Thus, biocontrol for miconia in Hawaii appears to be economically justifiable. This research should enable scientists, economists and policy makers to make informed decisions about the optimal management of Miconia calvescens in Hawaii.

working paper

Spatial Economic Analysis of Early Detection and Rapid Response Strategies for an Invasive Species

Economic impacts from invasive species, conveyed as expected damages to assets from invasion and expected costs of successful prevention and/or removal, may vary significantly across spatially differentiated landscapes. We develop a spatial-dynamic model for optimal early detection and rapid response (EDRR) policies, commonly exploited in the management of potential invaders around the world, and apply it to the case of the Brown treesnake (Boiga irregularis) in Oahu, Hawaii. EDRR consists of search activities beyond the ports of entry, where search (and potentially removal) efforts are targeted toward areas where credible evidence suggests the presence of an invader. EDRR costs are a spatially dependent variable related to the ease or difficulty of searching an area, while damages are assumed to be a population dependent variable. A myopic strategy in which search only occurs when and where current expected net returns are positive is attractive to managers, and, we find, significantly lowers present value losses (by $270m over 30 years). We find further that in the tradeoff between search costs and damages avoided, early and aggressive measures that search some high priority areas beyond points of entry even when current costs of search exceed current damages can save the island more ($295m over 30 years). Extensive or non-targeted search is not advised however.

working paper

Invasive Species Control over Space and Time: Miconia calvescens on Oahu, Hawaii

We use Geographical Information Systems (GIS) to map the current and future populations of an invasive species, Miconia calvescens, on the island of Oahu, Hawaii, and the potential damages to water quantity, water quality, endangered bird habitat, and native habitat housing endangered plants, snails, and insects. We develop a control cost function that includes locating and treating Miconia plants. Using optimal control theory, we find the spatially dependent optimal population levels of Miconia and the paths to these populations over time.

Published: Burnett, K. M., Kaiser, B. A., and Roumasset, J. A., 2007. Invasive Species Control over Space and Time: Miconia calvescens on Oahu, Hawaii. Journal of Agricultural and Applied Economics, 39 (October 2007), 125-132.

Working Paper version

Economic Impacts of E. Coqui frogs in Hawaii

Hawaii’s geographical isolation has resulted in the development of unique and fragile ecosystems in which the arrival of a new species may create dramatic changes in the ecology, and now the economy, of the islands. Successful establishment rates for new species before the arrival of humans in the early 1st millennium AD may have been as low as one new species every 10,000 years (Loope, 1997). Only one terrestrial mammal, a bat (now extinct), reached the island chain without human assistance. Many other suborders are unrepresented; for example, the islands have no native snakes or frogs.

working paper

Introductions of Invasive Species: Failure of the Weaker Link

The prevention of invasive species is modeled as a “weaker link” public good. Under the weaker link aggregation technology, individual contributions beyond the lowest level will still provide benefits, but progressively these benefits decline as contributions exceed the minimum. A two-region model is constructed, assuming incomplete information concerning costs of provision. We compare the results of the model to several benchmarks in order to gain insights regarding what we can expect countries to contribute to this transnational public good and how these contributions differ from the Pareto optimal level, given the technology and information structure of this special type of public good.

Published: Burnett, K. M., 2006.  Introductions of invasive species: Failure of the weaker link.  Agricultural and Resource Economics Review, 35 (1), 21-28.

working paper version

Optimal Prevention and Control of Invasive Species: The Case of the Brown Treesnake

This dissertation examines the optimal management of a nuisance species that threatens but is not thought to be prevalent in an ecosystem. The three central chapters focus on integrated prevention and control of the Brown Treesnake (Boiga irregularis) in Hawaii.


Learning-by-catching: Uncertain invasive-species populations and the value of information

This paper develops a model of invasive species control when the species’ population size is unknown. In the face of an uncertain population size, a resource manager’s species-control efforts provide two potential benefits: (1) a direct benefit of possibly reducing the population of invasive species, and (2) an indirect benefit of information acquisition (due to learning about the population size, which reduces uncertainty). We provide a methodology that takes into account both of these benefits, and show how optimal management decisions are altered in the presence of the indirect benefit of learning. We then apply this methodology to the case of controlling the Brown Treesnake (Boiga irregularis) on the island of Saipan. We find that the indirect benefit—the value of information to reduce uncertainty—is likely to be quite large.

Published: D'Evelyn, S. T., Tarui, N., Burnett, K. and Roumasset, J. A., 2008. Learning-by-catching: Uncertain invasive-species populations and the value of information.  Journal of Envrionmental Management, 89, 284-292.

working paper version

Models of Spatial and Intertemporal Invasive Species Management

Prepared for the NCEE Valuation for Environmental Policy: Ecological Benefits Conference April 23-24, 2007.

uhero project report

Economic lessons from control efforts for an invasive species: Miconia calvescens in Hawaii

Once established, invasive species can rapidly and irreversibly alter ecosystems and degrade the value of ecosystem services. Optimal control of an unwanted species solves for a trajectory of removals that minimizes the present value of removal costs and residual damages from the remaining population. The shrubby tree, Miconia calvescens, is used to illustrate dynamic policy options for a forest invader. Potential damages to Hawaii’s forest ecosystems are related to decreased aquifer recharge, biodiversity, and other ecosystem values. We find that population reduction is the optimal management policy for the islands of Oahu, Maui, and Hawaii. On the island of Kauai, where tree density is lower and search costs higher, optimal policy calls for deferring removal expenditures until the steady state population is reached.

Published: Burnett, K. M., Kaiser, B. A., and Roumasset, J. A., 2007.  Economic lessons from control efforts for an invasive species: Miconia calvescens in Hawaii. Journal of Forest Economics, 13, 151-167. 

Working Paper version

Spatial containment of invasive species: Insights from economics

Economics can clarify the discussion on invasive species in at least three ways. First is
through the use of incentives to change human behavior so as to enhance protection
against the introduction, establishment, and spread of invasive species across the world.
The second recognizes the public good characteristics of invasive species control, and
develops institutions to support the weakest members of our global community (Perrings
et al. 2002). The third component involves choosing optimal investment in invasive
species management across space, species, and time. This paper is a first attempt at
addressing the third component, optimal spatial containment of an invasive species.

working paper

Optimal Public Control of Exotic Species: Preventing the Brown Tree Snake from Invading Hawai‘i

This paper develops a theoretical model for the efficient establishment of economic policy pertaining to invasive species, integrating prevention and control of invasive species into a single model of optimal control policy, and applies this model to the case of the Brown tree snake as a potential invader of Hawaii.

working paper

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