How to monitor semi-natural key habitats in relation to grazing preferences of cattle in mountain summer farming areas: An aerial photo and GPS method study

Summer farming was formerly an important part of Norwegian husbandry and mountain areas have been used for grazing for hundreds of years. A decline in summer farming practices, during the twentieth century, has caused a large-scale encroachment of trees and shrubs leading to extensive landscape changes and decreased biodiversity. Therefore, in order to maintain the biodiversity in summer farm mountain areas, it is now necessary to detect, map and monitor remaining species-rich fragments, i.e. key habitats. It is also important to identify still grass- and herb-rich areas that can be successfully restored for grazing because of a new interest for summer farming. Field surveys in the re-growing mountain areas are extremely time consuming, as the concomitant terrain renders movement by foot arduous. A method was thus developed for detection of key-habitats and other grass and herb-rich habitats in such areas based on interpretation of coloured infrared aerial photographs (CIR). In addition, black-and-white aerial photographs, taken nearly 40 years ago, were used to identify past open land and pastures and thus in combination with the modern ones allow the identification of areas that exhibit a continuity in grazing. Interpretation keys were developed and vegetation maps were constructed. The interpretation from the aerial photographs was compared to detailed field control and the method was found to be efficient and accurate. The method gave useful information about the landscape history and continuity of grazing. The cattle’s movements were traced by GPS equipment mounted on a collar on the leading cattle, and their movements were later transferred to a map and analysed together with the vegetation map in a GIS. The results show that the cattle preferred to graze in the areas identified as most valuable and species rich. The developed method also makes it possible to identify areas for which pasture-restoration might be successfully achieved. Furthermore, the study revealed that there is a high correspondence between key habitats in the summer farming areas and grazing preferences of the cattle.