Conservation targeting under fragmentation: Evidence from the Dutch river area

Habitat connectivity is a prominent target of biodiversity policy, but it remains unclear which landscape margins matter most for conservation outcomes under scarce budgets. We study this question in the Dutch river area by comparing six connectivity metrics as predictors of occurrence for three red-listed species. Across species and specifications, habitat area shows the strongest and most consistent association with occurrence, while graph-based metrics add limited explanatory value. Because woody linear elements are especially prominent in current Dutch policy, we examine that margin more closely using an instrumental-variables strategy based on historical fragmentation and land-consolidation timing. The IV results provide no consistent evidence that woody linear elements improve species occurrence once endogeneity is addressed. An illustrative cost-effectiveness comparison further suggests that increasing habitat area dominates reducing isolation on the evaluated margin. Taken together, the results support prioritizing habitat expansion over stronger reliance on woody linear elements or more complex connectivity proxies in this setting.