Land-use abandonment owing to irrigation cessation affects the biodiversity of hay meadows in an arid mountain region

In arid regions, irrigation is required to secure agricultural production including the production of hay. The Valais, a dry inner alpine valley of Switzerland, has a long tradition of meadow irrigation. However, in the 20th century irrigation was stopped on marginal, poorly accessible areas usually accompanied by the entire abandonment of these meadows. The aim of this study was to examine the consequences of land-use abandonment resulting from the cessation of irrigation for the biodiversity of species-rich hay meadows in the Valais. We compared soil characteristics and species richness and composition, habitat specificity and functional traits of plants and gastropods of three serial stages of succession (each five hay meadows, early abandoned meadows and young forests). Soil moisture was lower in young forests than in the other two stages. Soil nitrogen content decreased following abandonment, which was due to the cessation of fertilization. The three successional stages did not differ in plant species richness but harboured distinct plant communities. Gastropod richness increased with progressive succession and species composition of hay meadows differed from those of the two other stages. The proportion of grassland (plants) and open-land (gastropods) species decreased following abandonment. Furthermore, meadow abandonment led to an increase in the height of non-woody plant species, a later start of seed shedding, a change in the type of plant reproduction and an increase in the shell size of gastropods. In conclusion, this study showed that extensive land-use, which is strongly linked to irrigation, is required for the characteristic species-rich hay meadows of this arid mountain region.