The core area concept is proposed as a criterion promoting the formation of contiguous areas of old growth over time in the landscape. Core area is defined as the area of old forest, free of edge effects, where the edge effect is a function of the state of the surrounding habitat. The core area measure is evaluated by solving a long-range planning problem for a landscape consisting of 200 stands, where the net present value of forest management is maximized under the constraint of a certain amount of core area in the landscape over a time horizon of 100 years. Simulated annealing is used as the solution technique. The results indicate that the degree to which stands are clustered depends on the amount of core area demanded and the extent of the edge width. The amount of new core area that is allocated adjacent to existing core area, indicating a continuity of core area formation, is increased with core area demand, the minimum age of old forest, and the existence of a U-shaped initial age structure. The cost of attaining the spatial patterns appears to be low compared with the cost of retaining the old forest.