Conserving red squirrels (Sciurus vulgaris):: mapping and forecasting habitat suitability using a Geographic Information Systems Approach

A model of habitat suitability linked to a Geographic Information System was developed for the red squirrel (Sciurus vulgaris) in 2800 ha of Thetford Forest, East England, to assess red squirrel population numbers in relation to forest management. We defined each forest sub-compartment or parcel of land in terms of its tree species and age between 1995 and 2015, and categorised each parcel of land as low, moderate or high red squirrel suitability. Resident squirrels may live in more than one habitat patch providing the distance between patches is within the foraging range of the animals and the land between the patches does not act as a barrier to foraging movements. Moreover, squirrels require a minimum area (home range area) of suitable habitat that will provide them with sufficient food resources. To examine these two factors, we explored 120 different model scenarios using three different distances to link patches together and four different sized minimum areas, termed minimum linked areas (MLA), that would hold resident red squirrels, at five year intervals between 1995 and 2015. As an overall measure of suitability, we summed all the MLAs in the reserve for high plus moderate suitability, which we have called the total linked area (TLA), and forecast how this may change in the future. We show that TLA will increase from 39% in 1995 to 67% of the study area by 2015, demonstrating that the reserve will get better for red squirrels over this time. We also demonstrate how changes in forest management would further increase TLA to 82% by 2015. Our results demonstrate how a habitat suitability model operating at the scale of an individual forest, coupled with a GIS and based on an understanding of the species' ecology, provides an objective way of assessing the impact of forest management prescriptions on red squirrel populations. (C) 2002 Elsevier Science Ltd. All rights reserved.