Experiment-based recommendations for biodiversity-friendly management of mountain hay meadows

Question: The biodiversity of mountain hay meadows has historically been maintained through traditional, low-intensity farming practices. In recent decades, however, agricultural intensification for hay production has led to dramatic declines in their biodiversity. This study asks: which management practices can contribute to maintaining the biodiversity value of mountain hay meadows without jeopardizing agricultural revenue? Location: Eleven semi-natural meadows, canton of Valais, inner Alps, southwest Switzerland. Methods: We experimentally measured the effects of various intensities of fertilization (slurry) and aerial irrigation (sprinklers) on the taxonomic, phylogenetic and functional diversity of plants. The experiment consisted of six different treatments, each randomly applied to one of six plots within a meadow. A plot therefore was (1) not irrigated and only fertilized with slurry, (2) not fertilized and only irrigated with a sprinkler, (3–5) receiving low, medium or high amounts of both fertilizer and water, respectively, or (6) receiving no input of irrigation or fertilizer (control plots). Results: After 4 yr, all biodiversity metrics were negatively impacted under the highestmanagement intensity (irrigation combined with fertilization at concentrations corresponding to the input necessary to achieve maximum local hay yield, i.e. three-thirds of inputs). In contrast, at low- and mid-intensity management levels (irrigation combined with fertilization at one-third and two-thirds of the maximum concentration, respectively) most diversity metrics did not differ from the controls, except for forb species richness, which was already reduced under mid-intensity management compared to low-intensity and control plots. Neither irrigation nor fertilization alone had a negative impact on plant biodiversity. Conclusions: Low to moderate agricultural intensification of hay production does not appear to be detrimental to plant biodiversity among mountain meadows. These results suggest that sustainable management would be obtained via irrigation and fertilization corresponding to one-third to two-thirds of the quantity necessary to achievemaximumlocal hay yield