Improving the spatial coherence of nature areas using genetic algorithms

Habitat fragmentation and habitat loss are causing many species to become locally extinct. The need to restore or conserve biodiversity has initiated plans in Europe—and, more specifically, in the Netherlands—to create networks of nature areas for the improvement of spatial coherence. In this paper spatial coherence is measured by the total boundary length of all nature areas. Spatial optimization is used to optimize the spatial coherence, in order to evaluate the so-called Dutch 2003 plans. The goal of the optimization is therefore to minimize the total sum of boundary lengths for all nature areas, while increasing the total surface area. Potential configurations have been calculated and compared with the 2003 plans, with respect to boundary length and the size of nature areas. The calculations have been performed by allocating increasing amounts of new nature to test if smaller numbers of hectares could yield a comparable perimeter decline. Optimization has been carried out separately (per province) and collectively (for all the Dutch provinces together). So-called genetic algorithms were used to tackle this strongly nonlinear problem. An interesting feature of the method used is its ability to optimize more than half a million variables—that is, potential nature cells. Allocating only half the area allocated in the 2003 plans resulted in a boundary-length decline of 30% compared with the 2003 plans, and yielded many more coherent areas than are found in the 2003 plans. Compared with the optimization per province, the collective optimization resulted nationwide in larger nature areas, across provincial borders. Considering the original aims, we can conclude that carrying out the 2003 plans will not improve the overall spatial coherence in terms either of the boundary length or of the number of areas and total surface area in the largest surface class. An additional advantage of the heuristic method discussed is that slightly different configurations can be found with almost the same characteristics in a relative short time. This will allow the provinces to choose the most suitable configuration.