Abstract
Land-use intensification is a major threat to biodiversity in agricultural grasslands and fertilization is one of the main drivers. The effects of fertilization on biodiversity and plant functional composition (community-weighted mean traits and mean ecological indicator values) are well studied in lowland regions, but have received less attention in mountain grasslands. Moreover, in inner-alpine dry valleys, fertilizer is often applied in combination with irrigation, and irrigation effects are less well known. We experimentally tested the effects of fertilization and irrigation on vascular plant species richness and the functional composition of mountain grasslands in the Swiss Alps. After five years, fertilization increased yield but the relationship was quadratic with maximum yield reached at intermediate fertilizer levels (58 kg N ha−1year−1). The species richness of all vascular plants and forbs decreased, on average, by 6 and 5 species respectively, per 50 kg N of extra fertilizer (ha−1 year−1) applied. Fertilization also favored fast-growing plants (increased mean specific leaf area) and plants typically found in productive environments (increased mean indicator values for soil productivity and moisture). In contrast, we found no effects of irrigation on plant community composition, which suggests that irrigation does not affect vascular plant diversity to the same extent as fertilization in these mesic mountain hay meadows, at least in the mid-term. Our finding that maximum yield can be achieved at intermediate fertilizer levels is very important from an applied, agronomical and conservation point of view. It suggests that without loss of yield, farming costs and at the same time environmental pollution and negative effects on biodiversity can be reduced by applying less fertilizer. We therefore recommend maintaining non-intensive land use and keeping fertilizer inputs as low as possible to maintain the high plant diversity of mountain grasslands.
Highlights
Grasslands cover wide areas of mountainous ecosystems in the Palaearctic, with cultural landscapes representing rich biodiversity hotspots, in particular in European massifs such as the Alps (Dengler et al, 2020)
Similar to functional response traits, ecological indicator values are widely used to characterize site conditions and temporal changes in vegetation plots (Diekmann, 2003; Boch et al, 2019b). In this five-years experimental study from the Swiss Alps, we investigated the response of yield, vascular plant species richness and functional composition to different intensities of slurry fertilization and sprinkler irrigation
We showed that diversity and functional composition of mesic mountain grasslands are highly sensitive to fertilization, but are rela tively resistant to irrigation
Summary
Grasslands cover wide areas of mountainous ecosystems in the Palaearctic, with cultural landscapes representing rich biodiversity hotspots, in particular in European massifs such as the Alps (Dengler et al, 2020). The major drivers of habitat degradation and loss of seminatural grasslands are land-use abandonment and intensification, which are causing a general decline in biodiversity and an increase in the number of threatened species (Dengler et al, 2020). Traditionally used grasslands have been largely replaced by fertilized grasslands, which can be mown frequently or grazed with high stocking densities (Boch et al, 2020). This land-use intensification is decreasing the biodiversity and alters species assemblages, leading to homogenization of grassland communities and reduced ecosystem multifunctionality (Allan et al, 2014; Hautier et al, 2018; Schirpke et al, 2020). While the effects of land-use intensification have been well studied in lowland regions, mountain grasslands have received less attention (Humbert et al, 2016)
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