Ranking of habitats for the assessment of ecological impact in land use planning Original Research Article

A simple habitat ranking method suitable for use in the early stages of land use planning is developed here. The method is designed for assessment of the biological impacts of infrastructure and urban development. The objectives are to formulate an assessment procedure, to minimise fieldwork and to avoid error due to species remaining unnoticed in the field. Ranking takes place in terms of a habitat value (HV) index calculated on the basis of the species present (vascular plants, amphibians, reptiles, birds and mammals), the threat categories to which they belong and the likelihood of their occupying specific habitats. The existence of the species in different habitats was predicted on the basis of the literature. To calculate the HV index, threat categories and preferred habitats were defined for each species, so that the species could be weighted according to their relative threat category in the region concerned. The method was tested in Finland (60–70° N), using several weights for each threat category in order to reveal the effect of differences in weighting. The results appeared to be relatively insensitive to the weights used, supporting the objectivity of the method. Herb-poor dry meadows, riparian habitats, herb-rich deciduous forests, industrial/urban habitats and cultivated areas were ranked highest in the southern regions of the country. Arctic alpine fells, riparian habitats, spruce mires and herb-rich deciduous forests were ranked highest in the northern-most region. In addition to potential species composition, the total area of a habitat and its vulnerability to the development concerned also has an influence on its ranking, and therefore separate rankings must be calculated for different types of development. The results suggest that habitat ranking of this kind could be profitable in the early stages of environmental impact assessment, because it helps one to concentrate on the most valuable habitats. It is also reasonable to assume that our method may be of help in evaluating Siberian boreal habitats by combining this method with geographical information systems.