Horse grazing has ability to maintain species richness in grasslands – study

More plant diversity seen in continuously grazed horse pastures in Germany compared to those grazed by cattle.
Photo by Rich Dahlgren

Horse grazing has the potential to maintain species richness in temperate grasslands, the findings of a fresh study in Germany suggest.

University of Göttingen researchers Anja Schmitz and Johannes Isselstein, writing in the journal Sustainability, said horses are of increasing relevance in agriculturally managed grasslands across Europe. However, there is concern over the extent to which grazing with horses is a sustainable grassland management practice.

“The effect of longer-term horse grazing on the vegetation characteristics of grasslands has received little attention, especially in comparison to grazing cattle,” the pair noted.

They set out to explore the relative importance of the grazing system and grazing species on grassland management, using the vegetation characteristics as an indicator for sustainable management.

The researchers monitored grassland vegetation across a range of paddocks in western central Germany. They compared paddocks grazed by horses under two different regimes – continuous versus rotational – to paddocks grazed by cattle managed under similar conditions.

On 156 paddocks, they found 179 plant species in total. The average species number per paddock in the designated sample areas was 57, ranging from 24 to 129.

They observed considerably more plant species and more High Nature Value indicator species on paddocks grazed continuously by horses compared to cattle. High Nature Value (HNV) grasslands are defined as grasslands with extremely high levels of biodiversity.

However, there were no significant differences in species richness or High Nature Value species richness between paddocks rotationally grazed by horses and those grazed by cattle.

The vegetation in cattle pastures was found to be more grazing tolerant and had higher forage value than in those continuously grazed by horses.

Regardless of the grazing system, the competitive component was lower, the stress-tolerant component higher, and the floristic contrast between patch-types stronger in the horse paddocks compared to the cattle paddocks.

Species richness was strongly influenced by the extent of the floristic contrast, they said.

Discussing their findings, Schmitz and Isselstein said an important finding was that species richness and botanical composition in horse-grazed paddocks are affected by the grazing regime – that is, continuous or rotational grazing – with significantly higher species richness on continuously grazed horse pastures compared to those grazed by cattle.

The finding that continuously grazed horse paddocks had significantly more High Nature Value species richness than the cattle pastures was also important, since less than 14% of grasslands in Germany have recently been evaluated as being of high nature value.

It was noteworthy, they said, that the horse paddocks showed more sward diversity than the cattle pastures, irrespective of the grazing regime.

This greater sward diversity meant there was a greater variety of varying environmental conditions (niches) at a small spatial scale, which allows a higher plant species richness on the paddock scale.

“Usually, farmers prefer rotational over continuous grazing because rotational grazing ensures a more uniform herbage utilisation, reduces the formation of patches of different sward height, prevents overgrazing and provides herbage of a higher quality.

“Our results on floristic contrasts, however, indicate that this approach may be less effective than assumed under horse grazing.

“The stronger patch-grazing effect under horse compared to cattle grazing indicates that maintaining homogenous swards with horses is much more challenging.

“Nevertheless, horse keepers do often not aim at maximising grassland yields and are thus able to tolerate a heterogeneous sward structure to some extent. This provides an opportunity for biodiversity in grazed grasslands.”

Because of their patch-grazing behaviour, horses are generally considered a more difficult grazer species than cattle, the authors observed.

“Several authors stress that horse grazing is associated with environmental risks. Our study did not confirm increasing risks, at least not in relation to the nature value of the horse-grazed grasslands.

“Our study demonstrated the potential of horse grazing to maintain species richness of temperate grasslands,” they said. “However, more in-depth research is required to better understand interactions of horse grazing, grazing regime and the landscape context.”

More plant diversity seen in continuously grazed horse pastures in Germany compared to those grazed by cattle.
File image

This, they said, would then provide a basis for a more targeted grazing management with horses for the benefit of species-rich grasslands in temperate climates.

Schmitz, A.; Isselstein, J. Effect of Grazing System on Grassland Plant Species Richness and Vegetation Characteristics: Comparing Horse and Cattle Grazing. Sustainability 202012, 3300.

The study, published under a Creative Commons License, can be read here

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