Grazing and Woody Encroachment Effects on Biodiversity and Carbon Storage of Grassland Ecosystems of the Berchtesgaden National Park (Grassland BGD)

Over the last 150 years, the decline in mountain agriculture led to abandonment and ecological succession of many mountain grasslands. The consequences are the loss of centuries-old cultivated landscapes and the associated unique biodiversity and ecosystem services that are important to society. Currently, the more productive and easily accessible mountain grasslands near the mountain huts are managed relatively intensively, while the more remote mountain grasslands are grazed less frequently and are therefore more susceptible to abandonment, shrub encroachment and, ultimately, reforestation. The trend towards a decline in mountain agriculture is partly due to a lack of staff, but also increasingly due to the accelerating effects of climate change.

According to experts, adaptation measures are therefore urgently needed. Biogeochemical processes in mountain ecosystems are more sensitive to temperature than in temperate lowland regions. Rising temperatures and an extended growing season lead to an upward movement of species, which in turn results in changes in species composition as well as nutrient stocks and fluxes. Previous studies have shown that increased N and P availability increases the proportion of graminoids at the expense of herbaceous plants and that in P-limited systems, root-related traits and mutualistic relationships with soil microbes such as arbuscular mycorrhizal fungi are critical for enhancing nutrient uptake in many plant species.

However, it is not yet clear how climate change and alternative grazing regimes affect the productivity of mountain grasslands: research from 2008 showed an increase in the growth and reproductive success of mountain grasslands compared to the 1980s. To avoid the invasion of woody plants, farmers want to start the grazing season earlier in mountain grasslands, which may be an adaptation strategy. This adapted grazing regime could in turn significantly alter biogeochemical cycles, biodiversity and ecosystem services. Two projects by the Bavarian Institute of Agriculture (LfL) have shown that early livestock grazing and adapted livestock density reduce weed establishment, but the impact on carbon storage has not been evaluated.

Building on previous results and good contacts with farmers, this project aims to investigate how the invasion of woody plants affects plant and insect species and soil carbon storage. The experimental setup includes a pairwise design with two treatments: encroachment with woody trees and no/negligible encroachment. For each treatment we established three transects and three survey plots along each transect. Vegetation surveys including species richness, cover, plant functional and agronomic parameters, and suction samples for insects have been conducted. In addition, soil biogeochemistry (including carbon, N and P stocks) will be analyzed and the main fluxes related to nutrient cycling and trace gases will be studied.

• Heavy woody encroachment reduces plant and insect diversity.
• Plant and insect diversity benefit from intermediate levels of woodland cover.
• High plant species diversity is associated with greater C, N and P stocks and a tighter nutrient cycle, which is reflected in lower CO₂ fluxes and losses of inorganic N and inorganic and organic P.

The project is funded by the Weihenstephaner AgrarAllianz as part of the AgroMissionHub 2024 funding project.