Experimental rewilding enhances grassland functional composition and pollinator habitat use

Semi-natural grasslands are rich in biodiversity and thus important habitats for conservation, yet they are experiencing rapid declines due to agricultural intensification and abandonment. Promoting a more diverse mammalian herbivore community, including large and megaherbivores, may result in positive cascade effects for biodiversity and ecosystem functioning. Therefore, reintroducing an ecologically functional substitute of an extinct large herbivore could mitigate current biodiversity declines and foster semi-natural grassland conservation. To test this hypothesis, we set up a 3-year rewilding experiment where 12 feral horses were introduced in three 10-hectare enclosure replicates (four horses per enclosure). We used community-weighted mean plant functional traits to elucidate plant community changes induced by grazing through time. We also investigated the effects of this experimental treatment on insect pollinated plants and on pollinator habitat use. The grassland community exerted a mixed tolerance/avoidance response to grazing. This resulted in plant functional compositional changes which favoured prostrate plant species with higher specific leaf area, characteristic of ruderal communities. Plant species richness was higher in grazed compared to ungrazed areas. Butterfly and bumblebee habitat use, as well as feeding and resting activities were also higher in grazed areas. Moreover, the number of pollinators increased with plant species richness.Synthesis and applications. This study demonstrates that, to enhance the diversity of a given herbivore community with ecological replacements of extinct wild horses can have significant effects on the functional composition of grasslands. It can also mitigate plant species declines, in particular bee-dependent plants, and boost pollinator habitat use. Novel management alternatives are urgently needed to reverse the negative effect of land abandonment in European agricultural landscapes. Thus, rewilding interventions with large mammalian herbivores may offset current biodiversity declines by maintaining important functional links between plants and pollinators in grassland ecosystems. Foreign Language AbstractSammanfattning Naturbetesmarker ar rika pa biologisk mangfald och ar darmed av stor betydelse for naturvarden. Tyvarr minskar arealen av dessa marker pa grund av intensifieringar inom jordbruket och andrad djurhallning. En variationsrik djurhallning med stora daggdjur kan resultera i positiva foljdeffekter for biologisk mangfald och mer funktionella ekosystem. Genom att aterinfora ekologiskt funktionella ersattare for utdoda stora vaxtatare kan vi pa sa vis minska forlusten av biologisk mangfald och gynna bevarandet av naturbetesmarker. For att testa detta genomfordes ett trearigt faunarestaurerings-forsok med 12 hastar som fick beta i tre stycken 10-hektar stora hagn (fyra hastar i varje). Vi anvande medelvarden av vaxtsamhallets funktionella egenskaper for att studera hur hastarnas bete forandrade vaxtsamhallet over tid. Vi studerade aven effekter pa insektpollinerade vaxter och hur pollinerande insekter nyttjade forsoksytorna. Vaxterna uppvisade en blandning av tolerans och undvikande som respons mot betandet, vilket resulterade i funktionella forandringar som gynnade lagvaxande arter med stora blad, sa kallade ruderatvaxter. Vaxtrikedomen var hogre pa betade ytor an pa obetade. Det var aven storre forekomst av fodosokande och vilande fjarilar och humlor pa betade ytor. Antalet pollinerande insekter okade med vaxtrikedomen.Syntes och tillampning. Var studie visar att vi genom en vildare djurhallning kan aterskapa hastens ekosystemfunktion och att det ger positiva effekter pa vaxtsamhallets funktionella sammansattning. En vildare djurhallning kan aven motverka forlusten pollinerade vaxter och oka mangden pollinerande insekter. Nya forvaltningsmetoder behovs for att vanda den genomgripande utvecklingen kopplat till igenvaxning av det europeiska jordbrukslandskapet. angstrom terforandet av stora vaxtatande daggdjur kan forhindra forlusten av biologisk mangfald och uppratthalla viktiga funktionella kopplingar mellan vaxter och dess pollinatorer i naturbetesmarker. This study demonstrates that, to enhance the diversity of a given herbivore community with ecological replacements of extinct wild horses can have significant effects on the functional composition of grasslands. It can also mitigate plant species declines, in particular bee-dependent plants, and boost pollinator habitat use. Novel management alternatives are urgently needed to reverse the negative effect of land abandonment in European agricultural landscapes. Thus, rewilding interventions with large mammalian herbivores may offset current biodiversity declines by maintaining important functional links between plants and pollinators in grassland ecosystems.