Browsing by Author "Liebhold, A. M."

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    Bioeconomics of managing the spread of exotic pest species with barrier zones
    Sharov, A. A.; Liebhold, A. M. (Ecological Society of America, 1998-08)
    Exotic pests are serious threats to North American ecosystems; thus, economic analysis of decisions about eradication, stopping, or slowing their spread may be critical to ecosystem management. We present a model to analyze costs and benefits of altering the spread rates of invading organisms. The target rate of population expansion (which may be positive or negative) is considered as a control function, and the present value of net benefits from managing population spread is the criterion that is maximized. Two local maxima of the present value of net benefits are possible: one for eradication and another for slowing the spread. If both maxima are present, their heights are compared, and the strategy that corresponds to a higher value is selected. The optimal strategy changes from eradication to slowing the spread to finally doing nothing, as the area occupied by the species increases, the negative impact of the pest per unit area decreases, or the discount rate increases. The model shows that slowing population spread is a viable strategy of pest control even when a relatively small area remains uninfested. Stopping population spread is not an optimal strategy unless natural barriers to population spread exist. The model is applied to managing the spread of gypsy moth (Lymantria dispar) populations in the United States.
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    Model of slowing the spread of gypsy moth (Lepidoptera : Lymantriidae) with a barrier zone
    Sharov, A. A.; Liebhold, A. M. (Ecological Society of America, 1998-11)
    When attempts to eradicate an introduced pest species fail and it becomes: established, barrier zones are often used to stop or to slow the spread of the population into uninfested areas. The U.S. Forest Service is currently conducting a Slow-the-Spread (STS) pilot project to evaluate the feasibility of slowing the spread of the gypsy moth (Lymantria dispar L.) in several areas along the population front. To predict the effect of barrier zones on the rate of gypsy moth spread we developed a model that assumes establishment of isolated colonies beyond the expanding population front. These colonies grow, coalesce, and thereby contribute to the movement of the population front. The model estimates the rate of spread from two functions: (1) colonization rate as a function of the distance from the population front and (2) population numbers in a colony as a function of colony age. Eradication of isolated colonies in a barrier zone was simulated by truncating the colonization rate function beyond a specific distance from the population front. The model predicts that eradication of isolated colonies in the STS project will result in a 54% reduction of spread rate. The actual rate of spread in the Appalachian Mountains has declined by 59% since 1990 when eradication of isolated colonies started. Thus, model predictions were close to the observed reduction in the rate of population spread.