Temporal Connectivity of Mature Patches in Forest Planning Models

We present a deterministic forest harvest scheduling model that ensures the temporal connectivity of mature forest habitat patches over time in a landscape managed for timber production. Past models have addressed the spatial aspects of habitat connectivity by requiring a certain amount of mature forest habitat to be retained throughout the planning horizon in contiguous patches of minimum size and age. These models do not recognize, however, that the dynamic patches of a managed forest ecosystem might not provide escape routes from "old" to "new" patches for certain wildlife unless there is temporal overlap among the patches. Biologists have suggested that the lifespan of patches is often more important than their size and contiguity for species survival. A mixed-integer programming formulation is proposed that guarantees overlap among patches of mature forest habitat that arise and disappear over time as the forest ages and is harvested. Four real forests are used to illustrate the mechanics of the approach and to show that the model is computationally tractable and in some cases even makes harvest scheduling models with minimum patch size constraints easier to solve.