Stopping grazing causes biodiversity loss

Stopping grazing causes biodiversity loss and homogenisation of soil food webs in mountain grasslands. A new study found that allowing animals like sheep and cows to graze to preserve biodiversity and soil health is very important. Stopping grazing is common in Europe and is expected to increase, especially in low-productivity, mountainous areas. There is concern that doing that in historically grazed ecosystems is causing a loss of rare species and an increase in common species, leading to overall declines in plant biodiversity. This loss of biodiversity can impact how ecosystems function.

Soil biodiversity is crucial for many ecosystem functions

There is growing evidence that stopping livestock grazing affects the biotic homogenisation of above-ground communities, such as plants and insects. However, much less is known about its effects on below-ground organisms. Soil biodiversity is crucial for many ecosystem functions, like decomposing organic matter, making nutrients available to plants, preventing nutrient loss, and maintaining soil structure. Some studies have looked at the impact of stopping grazing on below-ground communities in grasslands. Still, they often focus on specific groups of soil organisms, short periods since grazing stopped, or limited climate and soil conditions. Therefore, it’s important to understand better the long-term effects of stopping grazing on the composition and diversity of below-ground communities.

The findings of the study

This study analysed changes in vegetation and various soil organisms. By “cessation of grazing“, it is intended to stop grazing by domesticated herbivores like cattle or sheep, but not remove wild grazers like hares, deer, and voles. Twelve montane grassland sites along an 800 km north-south gradient in the UK have been studied, each with paired plots that were either historically grazed by sheep or had livestock excluded by fencing for 10-65 years. The study focused on montane grasslands because they are a significant part of the European landscape and have been grazed by sheep for centuries, supporting the sheep farming industry across Europe. Additionally, stopping livestock grazing is common in mountain regions of Europe, including the UK. It is a key aspect of land abandonment and rewilding, with potential but largely unknown effects on local diversity and the composition of below-ground communities among sites.

By analysing a large dataset of soil organisms, the study found that stopping grazing in montane grasslands with a long history of sheep grazing leads to significant declines in the diversity of soil organisms. When animals stop grazing, the diversity of many groups of soil microbes and fauna decreases, especially for rare species. Stopping grazing makes soil microbial communities more similar, but for soil fauna like nematodes and insects, the diversity between sites increases. Stopping grazing changes plants and soil properties, but the effects vary by location. The study found consistent patterns in how soil microbial and fauna groups respond to stopping grazing. Most soil fauna and microbial groups, except soil bacteria, showed a significant decrease in mean local diversity after grazing stopped, coinciding with a decline in local plant species richness. While most soil microbial communities became more homogenised and similar after grazing stopped, soil fauna communities diverged, becoming less similar.

The importance of grazing for healthy ecosystems

The results of this study show that extensive grazing is important for maintaining the biodiversity of below-ground communities, and stopping grazing can have negative effects, similar to what has been seen in above-ground invertebrate communities. Many areas in Europe are undergoing “rewilding,” which involves stopping historic livestock grazing and replacing it with wild grazers or rare cattle breeds. Grazing animals help maintain the diversity of underground communities, which are crucial for ecosystem health.

Stopping grazing in these areas negatively affects soil diversity, highlighting the importance of grazing for healthy ecosystems. The results suggest that removing domestic livestock might not increase the diversity of below-ground organisms, especially where wild herbivores are not reintroduced, due to the low current densities of natural grazers and browsers.