Issues relating to habitat fragmentation by highways were investigated. The English trunk road and motorway network contain 30,000 hectares of land, supporting a wide range of habitats on the soft estate associated with the road. The significance of these habitats for wildlife is discussed. Fragmentation to habitats caused by linear developments, the importance of minimum viable population size in habitat fragmentation, the significance of patches, interiors and edges, highways as corridor habitats and dispersal barriers, are explained. The direct and indirect influence of highway structures including pavements, safety fences and lighting are outlined. Animal behaviour in response to the road may prevent dispersion. Specific information is given for mosses, fungi, lichens and vascular plants and their propagules. Use of deicing salt has resulted in inland populations of salt-loving plants. The size of forests can markedly affect the number of species in them; for twice the number of species, 10-fold the land area is required. The requirement to assess the historical impacts of disturbance on habitats as well as current disturbances is outlined. International Union for the Conservation of Nature criteria for species under threat are outlined; a population may be regarded as severely fragmented if no sub-population contains more than 10-20% of the total population. Ways of alleviating severance of populations are discussed. In some cases the habitat disturbances caused by road construction provide habitats for unusual species. Habitat management may need to be complex if the habitat diversity associated with English highways is to be maintained. For the covering abstract see ITRD E124693.
Abstract