Constructing cell-based habitat patches useful in conservation planning

Given a raster of environmental or habitat values representing a landscape, we construct agglomerations of contiguous cells that constitute habitat "patches." This land-allocation problem has received inadequate attention in the academic literature and cannot be solved with commercial GIS packages. In our method, each patch begins from an initial "seed" cell and continues to accrete neighboring cells until it reaches a desired total habitat value. This may be interpreted as reaching sufficient biological value to create a territory viable for the reproduction and survival of some demographic unit of a species (e.g., mating pair, social group). This article presents a new method for generating/identifying feasible patches. Depending on the type and variety of habitat and on user-selected parameters, patches can vary substantially in shape and size. A patch or territory alone would not be considered sufficient for conserving a species. The eventual use of the patches is as candidates for land units to be selected in order to form a reserve system. Patches should be very useful for conservation-reserve planning, because they build ecological knowledge directly into the spatial units that would be considered as building blocks for a reserve system. We present results of our patch-building heuristic method for planning data from California.