Grazing by semi‐feral cattle and horses supports plant species richness and uniqueness in grasslands

Abstract

Question: How does naturalistic grazing (trophic rewilding with large herbivores), in contrast to mowing and free succession (no grazing), affect plant community composition and species richness in temperate grassland grazed by semi-feral cattle and horses?Location: Mols Laboratory, Denmark. Methods:We investigated grazing exclosures in the rewilding area of the Mols Laboratory, four years after its establishment. We focused on moist to dry grassland vegetation, that is, excluding scrub and woodland. Each experimental block consisted of five 5 × 9 m plots, representing four fenced treatments, that is, summer-only grazing, winter-only grazing, full exclosure with annual autumn mowing and full exclosure with passive succession. The matrix (the fifth treatment) was grazed by large herbivores at close-to-natural densities, that is, regulated bottom-up by the carrying capacity of the area. Hence, even the seasonal grazing treatments were grazed at close-to-natural animal density. Quantitative plant community composition was assessed using the point-intercept method in 25 × 25 cm quadrats, supplemented with biomass calibration models based on additional quadrats, in which above-ground plant biomass was harvested after recording and the material sorted to species and weighed. Uniqueness was assessed as the sum of inverse range sizes for constituent species (unicity). Results:We found an appreciably higher plant species richness in grazing treatments than under both annual mowing and full exclosure, but only minor differences between seasonal grazing treatments. Uniqueness was highest in year-round and winter-only grazing and lowest in summer-only grazing. The forb:graminoid ratio tended to be high in the winter-only grazing treatment, whereas annual mowing was associated with dominance of graminoids over forbs. Full-exclosure plots had accumulation of litter

Habitat use of rewilded horses and cattle as related to the functional and structural composition of plant communities in a European restored wetland ecosystem

“…Our results indicate that, contrary to some earlier findings (e.g., Eldridge et al, 2019) and the concerns of conservation managers, multi-species grazer assemblages in close-to-natural (i.e. 0.3-0.4 animals per ha) densities do not have a destructive impact on herbaceous plants, but are rather an effective tool in conservation management, in line with recent findings (Bonavent et al, 2023).…”

Substantial light woodland and open vegetation characterized the temperate forest biome before Homo sapiens

“…Our findings show that European forests included substantial open and light woodland elements and suggest an important role for processes that maintain open habitats. This may have important implications for European biota and particularly for rarer species that depend on open, intermediate, and disturbed landscapes ( 54 , 55 ). Consequently, common approaches to restoration, such as tree planting, risk creating unfavorable habitats for biodiversity that has evolved in heterogeneous landscapes ( 5 , 56 ).…”

The late-Quaternary megafauna extinctions: Patterns, causes, ecological consequences and implications for ecosystem management in the Anthropocene

“…As trophic rewilding is a young field the number of empirical studies on self-identified rewilding efforts remains limited, albeit strongly rising (Svenning et al, 2016;Hart et al, 2023). However, there are many empirical studies on the ecosystem effects and biodiversity outcomes of de facto trophic rewilding, especially in Europe, North America, and southern Africa, often under names such as year-round or extensive grazing, or reintroductions, e.g., with many showing positive biodiversity effects (especially for plants) attributable to bison (e.g, Ratajczak et al, 2022) or feral and semiferal cattle and horses (e.g., Konvička et al, 2021;Dvorský et al, 2022;Bonavent et al, 2023;Köhler et al, 2023). Further, several long-term cases of megafauna recovery that did not necessarily emerge out of rewilding principles show how trophic rewilding can result in largescale top-down effects on ecosystems, for example vegetation changes in response to the reestablishment of white rhinoceros (Ceratotherium simum) (Cromsigt and te Beest, 2014) and African savanna elephants (Gordon et al, 2023).…”