Estimating habitat isolation in landscape planning

Habitat patches situated amidst an otherwise inhospitable landscape are often considered as islands in the sense of the equilibrium theory of insular zoogeography. Their species richness can be affected by isolation from other areas of suitable habitat. However, the isolation of habitat islands is not only dependent on the distance from the source area, as with oceanic islands, but also on the characteristics of the interjacent landscape. To account for the latter, the use of a measure of isolation termed ‘minimal cumulative resistance’ (MCR) is proposed. A simple model is described for calculating MCR from a grid-based map on which estimated dispersal resistances are assigned to landscape types. Application of the model is illustrated with a specific case: the allocation of new forests in the western part of the Netherlands. Although its application is bound by a number of restrictions, it is concluded that the model can be a useful aid in physical planning and nature conservation.