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

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.