In recent decades, Switzerland has experienced extensive urbanisation. Today, almost 5,3 million Swiss people live in urban areas. In such intensively used landscapes, semi-natural habitats are restricted to small areas, and biodiversity is greatly endangered. Ecological planning has the challenging task of meeting the needs of both humans and the natural environment. We review current scientific knowledge on the ecological and social effects of landscape fragmentation. We focus on densely populated regions in Central Europe and summarise this knowledge in an interdisciplinary synthesis. This review serves as a basis for planning strategies in intensively used landscapes, which are geared to both fulfilling the needs of local human populations and fostering biodiversity.
The effects of habitat fragmentation on biodiversity have been studied for several decades, but the mechanisms and specific effects of fragmentation are still not clear. The effects of the reduction of habitat area on biodiversity have been much better evaluated and seem to be stronger than the effects of fragmentation. Hence, the amount of available habitat is judged to be more important, at least in the short-term, for the persistence of animal and plant populations than the spatial configuration of habitat patches. In densely populated areas, however, urban land-use enhances the effective isolation of habitats by impeding migration and gene flow among populations.
In contrast to the large body of ecological and landscape ecological research performed in recent decades, there is not a single study focussing on the effects of landscape fragmentation on humans. Current findings in landscape aesthetics show that landscapes and certain landscape elements serve as a kind of external memory, reminding people of their experiences, skills, values and social affiliations. Natural and anthropogenic landscape elements enhance landscape preferences and contribute to place attachment and identity. In densely populated areas, the presence, quality and accessibility of recreational areas are important landscape values. Roads may serve as barriers for pedestrians and reduce the accessibility of such recreational areas and impede people being physically active locally.
Landscape indices can potentially link landscape patterns to ecological processes and to visual aspects of people's landscape preferences. This makes them potentially important indicators in policy and planning. Furthermore, landscape indices are required to identify critical threshold values to denote the point at which formerly continuous landscapes abruptly become fragmented. However, most of the indices used to quantify landscape fragmentation have not been tested and validated in empirical studies and their ecological relevance is thus still under debate. Recent findings indicate that specific landscape indices are implementable in planning and deciding on policy if they are combined with qualitative indicators. Threshold values of landscape fragmentation, however, have not yet been validated in empirical studies, which means their application at present cannot be recommended. We hope our review contributes basic knowledge to the maintenance and future enhancement of human dominated landscapes.