Trophic rewilding by large herbivores reduces plant nitrogen and water limitation across seven sites irrespective of their edaphic conditions

Abstract

Based on a growing understanding of the role of wild megafauna in the functioning of natural ecosystems, trophic rewilding by large herbivores is increasingly used as a nature-based solution to mitigate biodiversity loss and climate change in Europe and beyond. Despite the growing interest in implementing nature-based approaches to restore key non-productive ecosystem services, there is relatively little data available to assess the benefits and risks of rewilding projects. We therefore investigated the effects of year-round grazing by large ungulates on plant biomass characteristics and their relationship with soil properties at seven trophic rewilding sites in the Czech Republic. We found that trophic rewilding systematicaly reduced aboveground biomass, but improved plant nitrogen supply through enhanced nitrogen recycling, resulting in higher water and nitrogen content in the aboveground plant biomass and providing high-quality forage for grazing ungulates. Belowground biomass remained unchanged, indicating that the current grazing intensity allowed sufficient plant regeneration and organic matter input into the soil, increasing soil organic matter sequestration and water retention capacity. Rewilding further altered plant-soil interactions and strengthened the relationship between vegetation and soil microbial processes, which improved root growth and phosphorus uptake. These newly emerged herbivore-vegetation-soil interactions are of critical importance, as phosphorus and water availability have been identified as important edaphic factors controlling plant productivity and forage quality of rewilded sites. We propose that close herbivore-plant-soil relationships may promote the dynamics and self-regulatory capacity of rewilded ecosystems and facilitate their ability to promptly respond and adapt to changing biospheric and climatic conditions.