invader can cause. Since its introduction in the mid-twentieth century it has caused the extinction of 12
of the island 's bird species [Savidge, 1987; Rodda, Fritts and Chiszar, 1997].
Biological invasions occur almost everywhere. They comprise a significant component of global
environmental change [Vitousek et. al., 1996] and are viewed by some as one of the most important
issues in natural resource management today [Williams and Meffe, 2000]. As a consequence, the past
decade has seen a sizeable growth in public policy directed toward invasive species.1
In spite of the growing concern with invasive species, scientific understanding of the relation
between economics and ecology in the control of biological invasions is not well-developed. The
purpose of this paper is to examine the economics of controlling a biological invasion. We analyze the
optimal control policy in a dynamic model of invasion by a single species. The aim is to understand the
intertemporal economic and biological tradeoffs that determine the extent to which an invasion should be
controlled at any point of time. A clear understanding of how economic and ecological factors interact to
determine the optimal policy is important because a wide range of outcomes is possible, even in a simple
one-dimensional model. The paper focuses on the conditions under which it is optimal to eradicate an
invasive species and conditions under which eradication is not optimal. The results characterize
both of these possible outcomes in terms of joint properties of the biological growth of the invasion,
control costs, damages and the social discount rate.
1In 1990 the U.S. Congress passed the Nonindigenous Aquatic Nuisance Prevention and Control Act to
deal with the increasing problems of invasive species in waterways. In 1996 the act was amended to become the
National Invasive Species Act. In 1992 the Alien Species Prevention and Enforcement Act was passed to protect
Hawaii from the introduction of prohibited plants, plant pests and injurious animals that may be contained in the
mail. On Feb 3. 1999, President Clinton signed Executive Order 13112 which created the National Invasive Species
Council. Subsequently, the Council drafted the National Invasive Species Management Plan to develop a national
strategy for combating problems of invasive species. There has also been increasing concern at the international
level. In 1997, the Global Invasive Species Programme was established by the Scientific Committee for Problems of
the Environment (SCOPE), in collaboration with the United Nations Environment Programme, The World
Conservation Union, DIVERSITAS (an international programme on biodiversity science) and the Commonwealth
Agricultural Bureau International.