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Taxonomic and functional vegetation response to no-grazing, seasonal grazing and year-round grazing

Søndergaard, Skjold Alsted1; Fløjgaard, Camilla1

Published Mar 24, 2025 on Dryad. https://doi.org/10.5061/dryad.ns1rn8q37

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Mar 24, 2025 version files 202.49 KB

Abstract

Grazing by domestic herbivores is applied across Europe to combat the loss of light-dependent, species-rich communities due to encroachment by competitive woody and herbaceous plants. However, the billions of euros spent annually by the EU on grazing subsidies have failed to halt the loss of species in open habitats. We hypothesized that typical agri-environmental seasonal grazing fails to simulate the ecological effects of now-extirpated, large, wild herbivores, which coevolved with these species-rich communities. We conducted a survey of 30 semi-natural sites where grazing was either absent, seasonal, or year-round, across a spectrum of abiotic conditions. We recorded plant species diversity and cover and used plant traits to assess taxonomic and functional responses. Year-round grazing increased plant species richness and forb cover compared to seasonal or no grazing. Correspondingly, dormant-season (winter) grazing pressure affected species richness and forb cover more strongly compared to growing-season (summer) grazing pressure. Functional richness was similar across management types, likely due to higher plant trait similarity in year-round grazed sites. Our results support that grazing weakens interspecific competition among plants, while dormant-season grazing appears to allow diverse forb communities to replace species-poor grass dominance.

Synthesis and applications: Our results indicate that typical, seasonal grazing may be counterproductive, in terms of promoting plant diversity. We found the most effective management strategy for conserving species-rich forb communities to be year-round grazing. Species losses linger on and are especially high for European species that depend on open and semi-open, forb-rich habitats such as grasslands, wetlands, and woodlands. To halt this trend, we advocate a shift in conservation strategies towards natural grazing and a greater focus on the ecological and evolutionary mechanisms behind the relationship between large herbivores and plants, not least the balance between grasses and forbs.