Rewilding with large herbivores: The importance of grazing refuges for sapling establishment and wood-pasture formation

- Rewilding aims to restore ecological processes with minimum human intervention.
- It can be applied on abandoned agricultural lands to restore wood pasture landscapes.
- We studied effects on sapling establishment in Europe's oldest rewilding area.
- We found that grazing refuges are essential for sapling establishment.
- Rewilding projects should warrant grazing refuges for wood pasture restoration.

Rewilding is a novel nature management type that aims at restoring natural processes with minimal human intervention. It is increasingly employed on abandoned agricultural lands in Europe, but empirical studies are scarce. Rewilding may lead to formation of wood-pastures, arguably the primeval landscape in parts of Europe before Neolithic times. We investigated sapling establishment, a key process for wood-pasture formation, in the Oostvaardersplassen: Europe's oldest large-scale rewilding area, with high densities of free-roaming large herbivores. We transplanted saplings of pioneers, spiny shrubs, and hardwood species and studied how herbivore accessibility (grazed control, partial and full exclosure), vegetation type (tall roughs; short lawns) and soil-tillage (mimicking wild boar rooting) affected sapling survival for four years. No single sapling survived in grazed controls, while survival in exclosures was 25%. Differences in survival between partial and full exclosures were minor, indicating that reduced herbivore access is sufficient for sapling survival. Survival was higher in lawn than in rough in both exclosure types and for all species, indicating positive effects of preceding grazing. Soil tillage initially benefitted all species, but effects lasted for pioneers only, suggesting that - once introduced - wild boar rooting may affect woody species composition. We conclude that rewilding with herbivores can successfully form wood-pasture landscapes on abandoned agricultural land as long as grazing refuges are present that allow for sapling establishment. As grazing refuges are generally lacking on abandoned agricultural lands, where most rewilding is foreseen, we recommend that future projects consider the presence - or creation - of grazing refuges.