Vegetation dynamics following three decades of trophic rewilding in the mesic grasslands of Oostvaardersplassen

Abstract

Aim: There is increasing interest in open-ended restoration with the focus on restoring natural processes rather than static compositional goals. Here, we investigated vegetation dynamics in response to three decades of trophic rewilding with large herbivores in a recent anthropogenic, fertile 55-km2 landscape on reclaimed marine sediments. This site provides important insights into plant community assembly in rewilded, young ecosystems. Location: Oostvaardersplassen, the Netherlands. Methods: Using field surveys and vegetation data spanning two decades, we investigate vegetation dynamics of the mesic grasslands in Oostvaardersplassen, a pioneer trophic rewilding site in the Netherlands. To identify the effects of grazing and other ecological processes, we include comparisons to an adjacent ungrazed control site and to the dark diversity, that is, missing species expected to be present given the environment and geography. Results: The impact of large herbivores has led to a more open and homogenous vegetation with higher plant species richness in the mesic grasslands of Oostvaardersplassen compared to the ungrazed control. Compared to species in the dark diversity, the species present are more common in the region, more stress-tolerant, and less competitive, in line with joint effects of grazing and immigrational lag. Conclusions: The changes in vegetation composition and structure show that rewilding with large herbivores promotes the prevalence of stress-tolerant and low-statured plant species, which are in decline in the broader landscape while reducing the dominance of otherwise widespread, competition-adapted species. The absence of numerous rare species suggests that dispersal limitation poses an important constraint for the diversity build-up in anthropogenically isolated natural areas, necessitating active species introductions to mitigate this issue in the short to medium term.