Rooting by wild boar can help maintain biodiversity in priority calcareous grasslands, but management must be considered carefully

Calcareous grasslands are ecologically important, threatened and relatively rare ecosystems formed on chalk or limestone soils. When maintained in a conservation-sensitive manner, they support high species diversity. Consequently, these habitats are listed in Annex I of the EU Habitats Directive, requiring EU members states to designate, protect and manage them. However, the quality and abundance of calcareous grasslands has declined significantly in Europe over the last century, due to changing land use and management, and the transition of grassland into woodland, both naturally and through tree planting. https://environment.ec.europa.eu/topics/nature-and-biodiversity/habitats-directive_en

Calcareous grasslands are predominantly semi-natural habitats, meaning they need some level of ongoing management to maintain their characteristic features. Historically this was achieved through farm animal grazing and haymaking. However, agricultural abandonment and a reduction in livestock farming have led to changes in management practices in many areas across Europe. In the absence of these activities the grassland would typically undergo a process known as ecological succession. This involves the gradual natural replacement of low-growing plants by taller plants, then scrub, trees and finally woodland.

Native wild mammals such as red deer (Cervus elaphus) and wild boar (Sus scrofa) may slow down or even reverse the succession process through grazing, browsing and other forms of habitat disturbance.

In the case of boar, the main impact is through rooting - turning over the plant litter layer to search for food items such as roots, insects and fungi. Existing studies on the impact of boar rooting on plant communities have mainly focused on the impacts of boar outside of the species' natural range, where it is often considered an invasive species. Some studies have suggested that ground rooting behaviour by boar could have positive ecological effects in calcareous grassland within these animals' natural range.

In this study, researchers investigated the impact of boar rooting on the plant community in their natural range. They studied 60 pairs of plots, half of which were rooted by boar during winter and half were not. They surveyed summer vegetation cover including bare soil, plant litter, moss, grasses and herbs.

The study took place in Hainich National Park in the German state of Thuringia. This 7,500-hectare park contains 600ha of semi-open calcareous grassland. It was historically grazed by sheep until 1997. Following the non-interventionist principle of "Natur Natur sein lassen" (let nature be nature) the area has been left without any regular management since then.

The researchers identified 155 plant species across rooted and control plots, including three red-listed threatened species. They found that species richness and diversity were both higher in the rooted plots than in the controls during June and July. The ungrazed plots showed a lower number of dominating grass species, and a more advanced successional stage. The boar-rooted areas had more bare soil and more herbs, less plant litter, less moss, less dominant grasses and fewer shrubs than the boar-free areas.

Overall, bare soil areas, rooted by boar, supported calcareous grassland plant species. The boar-free areas contained less bare ground than the boar-rooted areas. However, where bare ground was more common, it was associated with fewer species. The researchers suggest this may have been because the amount of bare soil exposed by the rooting sometimes exceeded the optimal level, meaning plants struggle to colonise or need more time to colonise the bare ground.

These results suggest that rooting by wild boar can help to slow the succession process in threatened calcareous grassland. The researchers recommend that the management of such areas recognises this and allows for controlled levels of boar rooting to continue. They note, however, that additional actions may be required to adequately maintain the integrity of these ecosystems. They suggest that this could include grazing some areas with domestic livestock - as is already done in some places in the National Park - while leaving natural processes to lead in others.

The researchers recognised that, if left unchecked, wild boar populations could increase to levels that would create excessive disturbance and pose a further risk to the ecosystem. They therefore recommended careful monitoring of wild boar populations.

Source:

van Leeuwen, B. O., Tuinder, Q., Fartmann, T., Scherer, G., Klamm, A., Schellenberg, M., Vergeer, P., Jansen, P. A. (2025) Effects of wild boar (Sus scrofa) rooting on abandoned calcareous grassland in Hainich National Park, Germany. Global Ecology and Conservation 59:e03535

www.sciencedirect.com/science/article/pii/S2351989425001362