Environmental heterogeneity, biodiversity and agriculture in the wood-pastures of the Swiss Jura mountains

Wood-pastures are a traditional agricultural landscape from the Swiss Jura mountains, where cattle graze within dispersed trees and shrubs. This agroforestry system was originally meant to exploit both wood and animal products. However, today, wood-pastures’ persistence is threatened due to land use intensification or land abandonment, phenomena common to many mountainous areas. The environmental heterogeneity created by the presence of trees
and shrubs on pastures, as well as the irregular micro topography of the wood-pastures’ landscape makes them host to a unique biodiversity. While such a context offers a great opportunity to study links between environmental heterogeneity and biodiversity, it is also crucial, from an applied perspective, to identify which key elements of the wood-pastures have the potential to promote the diversity of different groups of species, as well as species of conservation concern, to target conservation strategies. Additionally, grazing activity is central in wood-pastures, and it is imperative to better understand how it is linked with environmental heterogeneity and biodiversity and to find synergies between conservation goals and agricultural production.
In this thesis, I studied pastures distributed along a gradient of tree and shrub cover, on the Jura mountains of the canton of Neuchâtel. I investigated how different parameters of environmental heterogeneity influence the composition and diversity of communities of birds, hoverflies and ground beetles. Following, I targeted an emblematic species of the wood-pastures, woodlark (Lulla arborea), which is threatened in Switzerland. Through a habitat selection model, I aimed to show which were the crucial environmental parameters for the bird occurrence and how agricultural intensification could threaten its persistence. The last objective of this thesis was to better understand how farmers adapt their grazing system to the heterogeneous environment of the wood-pastures and therefore how heterogeneity directly or indirectly (through grazing systems) impacts botanical communities.
I showed that tree cover was the main driver of species composition of birds and hoverflies on wood-pastures, with increasing percentage of tree cover being related to diversity of both groups of species. Yet I highlighted that bird ommunities and species diversity were, in addition, influenced by heterogeneity in tree stands’ structure and composition, which was not the case for hoverflies. Functional trait distribution of ground beetles’ communities as well as their biomass was also influenced by tree cover, and extensively used pastures contributed to higher species diversity of ground beetles. Following, I showed that, in wood-pastures, woodlark favors areas of smooth terrain, with a moderate tree cover and the presence of rocky outcrops, and that large fertilized surfaces were avoided by the species.
Lastly, I demonstrated that more rugged terrain was associated with less intense grazing systems and species-rich botanical communities, while trees on pastures promote diversified plant communities as well, through reducing competitive grassland species associated with high grazing pressure and enriched soils. These findings bring additional insights about the link between environmental heterogeneity and biodiversity, while highlighting the high value of wood-pastures for biodiversity through key environmental parameters. This thesis underscores the importance of accounting for the interconnections between agriculture, landscape heterogeneity, and biodiversity to develop and promote sustainable agricultural practices.

Thesis committee:
Prof. Dr. Delphine Clara Zemp (thesis director) - University of Neuchâtel, Switzerland
Dr. Kurt Bollmann - Eidg. Forschungsanstalt für Wald, Schnee und Landschaft (WSL), Switzerland
Prof. tit. Christophe Praz - University of Neuchâtel, Switzerland
Defended on th 22nd of May 2025
N°3203