Reducing forest fragmentation in long-term forest planning by using the shape index

The fragmentation of old forests is an aspect of forest development that has to be considered in long-term forest planning. Although several measures of the spatial structure of forests have been reported in the literature, very few have been evaluated with respect to their usefulness in long-term forest planning. The objective of this study was, therefore, to investigate if it is possible to use of one of these measures, the shape index, as a criterion in the optimization model for decreasing the fragmentation of old forest in the landscape The shape index is evaluated by solving a two-objective problem with simulated annealing, which aims at maximizing the net present value and minimizing the shape index for a landscape consisting of 924 stands. In a case study, the stated problem was converted to a one-objective problem by weighting the two objectives together. The study showed clear differences in the spatial patterns of old forest between the different weight combinations. With a higher weight on the shape index, the old forests become more clustered and the number of small and isolated patches of old forest decrease compared with a low weight on the shape index. The results also indicate that it is possible to considerably improve the shape index with only a small sacrifice in net present value. It is also clear from the case study that the shape index is a computationally well-behaved measure to use in optimization. The solution times for the different cases were generally very short.