Grazer effects on plant species richness and tree debarking within orchard pastures

Orchards are traditional agroforestry elements in agricultural landscapes and valuable for nature conservation in Europe. However, their diversity is endangered due to farmland intensification or abandonment. Grazing management promotes plant species diversity but grazers are suspected to harm trees through debarking. We studied 42 orchards within the Rhenish uplands (Germany) and compared horses, cattle and sheep grazing. We analysed how grassland diversity is promoted by the presence of trees and modified by grazing management, as well as how grazers may impact trees. Plant species richness benefited from tree presence, but was not affected by tree-cover and only slightly by grazer species, whereas grazing intensity showed significant negative effects. All grazer species significantly increased recent debarking in the absence of individual tree-protection. Therefore, maintaining species diversity and long-term tree persistence in orchards does not primarily depend upon grazer species, but more especially on grazing intensity and tree-protection.