Potential Effects of a Forest Management Plan on Bachman's Sparrows (Aimophila aestivalis): Linking a Spatially Explicit Model with GIS

By combining a spatially explicig individual-based population simulation model with a geographic information systerrg we have simulated the potential effects o f a US. Forest Service management p lan on the population dynamics o f Bachman's Sparrow (Aimophila aestivalis) at the Savannah River Site, a U.S. Department o f Energy facility in South Carolir~ Although the Forest Service's management p lan explicitly sets management goals for many specie& most o f the prescribed management strategy deals with the endangered Red-cockaded Woodpecker (Picoides borealis) because o f legal requirements. We explored how a species (the sparrow) that is not the target o f specific management strategies but that shares some habitat requirements with the woodpecker, would fare under the management plar~ We found that the major components of the proposed management p lan may allow the sparrow population to reach and exceed the m i n i m um management goal set for this specie& but only after a substantial initial decline in sparrow numbers and a prolonged transition period, In the model, the sparrow population dynamics were most sensitive to demographic variables such as adult and juvenile survivorship and to landscape variables such as the suitability o f young clearcuts and mature pine stands. Using various assumptions about habitat suitability, we estimated that the 50.year probability o f population extinction is at least5% or may be much higher i f juvenile survivorship is low. We believe, however, that modest changes in the management plan might greatly increase the sparrow population and presumably decrease the probability o f extinctior~ Our results suggest that management plans focusing on one or a f ew endangered species may potentially threaten other species o f management concerr~ Spatially explicit population models are a useful tool in designing modifications o f management plans that can reduce the impact on nontarget species of management concer~ Impactos potenciales de un plan de manejo del bosque sobre los gorriones de Bachman (Aimophila aestivalis): vinculando un modelo espacialmente explicito con SIG Resumen : Hemos simulado los impactos potenciales de un plan de manejo del Servicio Forestal de los Estados Unidos, sobre la dindmica poblacional del gorri6n de Bachman (Aimophila aestivalis) en un sitio de Savannah River, que es propiedad del Departamento de Energia de los Estados Unido& en Carolina del Sur La estrategia utilizada combtn6 un modelo de simulaci6n espacialmento explicito de las individuos miem. bros de la poblaci6rg con un Sistema de Informaci6n Geogrdfico. Si bien el plan de manejo del Servicio Foresta~ explicitamente establece medidas de mango para varias especie& debtdo a requerimientos legales la mayoria de las estrategias de manejo prescripta~ consideran al pdjaro carpintero de cucarda coloradd (Picoides borealis) en peligro de extinci6r~ Exploramos como se desenvolveria dentro del plan de manejo, una especie (el gorri6n), que no estd en la mira de ninguna estrategia especifica de manc~o, pero que comparte algunos de los requerimientos de habitat con el pdjaro carpintero. Encontramos que los componentes mds importantes del p lan de rnanejo le permiten a la poblaci6n de gorriones llegar y exceder la metal minima trazada para esta especie, pero s6lamente despuds de una disminacion sustancial en el nt~mero de gorriones y de un pro longado periodo de transici6n. En el modelo, la d indmica de pob lac i6n * Current address: Department of Fisheries and Wildlife, Michigan State University, East Lansing 311 48824. ~Current address: The National Biological Survey, Department of the Interior, Matlstop 3070-MIB, 1849 C Street N.W., Washington, DC 20240, USA Paper submitted February 24, 1993; revised manuscript accepted March 1, 1994.