Introduced grazing in Western-European coastal dune systems: a review of the effects on flora and fauna

Abstract

Western European coastal dunes are vulnerable ecosystems that are at risk of losing valuable biodiversity due to a decrease in dune dynamics and an increase in vegetation encroachment. This poses a threat to the flora and fauna of Natura 2000 priority habitat types related to open, dynamic coastal dune systems. Introduced grazing with animals such as horses, cattle, and sheep is used to reduce encroachment, with their effect depending on the used grazing regime, grazing pressure, and species assemblage. To assess the impact of introduced grazing on Western-European coastal dune systems, a literature review is conducted. This review assesses the impacts of grazing on flora and fauna in coastal dune systems in Western Europe, including areas managed by PWN in the Netherlands. The objective was to determine whether the effect of grazing in Western-European coastal dune systems is similar to that observed in PWN-managed areas. Results of this literature review shows that the effects of introduced herbivores on flora and fauna are complex and context specific. However, grazing has overall been found to enhance plant diversity and reduce the abundance of species linked to encroachment while promoting the growth of herbaceous indicator species linked to the conservation of that specific habitat. The impact on vegetation structure differs across studies, but in most cases grazing increases the openness and reduces shrub cover. Grazing has a neutral or positive effect on butterfly richness and abundance, but the impact on other invertebrates depends on their habitats and requires more monitoring to be concluded upon. Extensive grazing has a mixed effect on breeding birds, depending on the preferred habitat of the bird species. The findings from studies conducted both inside and outside of PWN areas suggest that the impacts of grazing are varied. Local context and external factors strongly influence the impact of grazing. Environmental factors may have a greater impact on flora and fauna than introduced grazers. Due to the difficulty in generalizing results across different systems, a better understanding of the interactions between grazing, habitat, and external processes is crucial for the effective management and conservation of coastal dune ecosystems.