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Even in sunny forest gaps, browsing by roe deer prevents the natural regeneration of many tree species. Researchers at the University of Würzburg show just how strongly these ungulates shape forest development.
In the current issue of the Journal of Applied Ecology, researchers from Julius-Maximilians-Universität Würzburg (JMU) report that roe deer restrict the natural regeneration of deciduous forests far more than previously assumed. The team led by Professor Jörg Müller demonstrated in a multi-year field experiment that even when large amounts of light enter the forest after disturbances, this advantage cannot compensate for the selective browsing by deer.
Browsing Overrides the Positive Effects of Light
To increase forests’ ability to adapt to climate change, forestry practice is increasingly relying on greater tree-species diversity. Open canopy gaps caused by storms or droughts generally provide ideal conditions for many species. “However, we found that the impact of roe deer is particularly pronounced in these lighter areas,” explains Ludwig Lettenmaier, a doctoral researcher at the University of Würzburg.
University Forest as a Prototype
The study was conducted over four years in the Würzburg University Forest. The researchers established paired plots – one fenced and one unfenced, each measuring 36 square metres – both in artificially created canopy gaps and in shaded, closed forest areas.
The results were clear: “The additional light could not offset the negative influence of the deer on the unfenced plots. Tree-species diversity was similar to that in the shaded areas,” says Lettenmaier.
Potentially high tree-species diversity developed at heights up to 1.3 metres, which is the level at which deer feed and browse. However, due to the animals’ selective browsing, only a few species managed to grow beyond this susceptible zone. Regardless of light availability, this led to a halving of tree-species diversity.
The study shows that roe deer, through their feeding preferences, drive a marked homogenisation of forest regeneration. Since deer densities in the University Forest are typical of many Bavarian deciduous forests, the researchers expect similar effects to occur on a wider scale.
Implications for Forest Management
After disturbances, the early developmental phase determines the future composition of forest stands. “If, in the first years, mainly less palatable species prevail, this will shape tree-species composition in the long term,” explains Jörg Müller, Professor of Conservation Biology and Forest Ecology. “Where deer densities cannot be adequately controlled, affected areas should be fenced for several years to allow the forest’s natural potential for greater diversity to unfold.”
The findings provide valuable insights for integrated wildlife and forest management. They also demonstrate that light and browsing must not be considered separately when assessing the resilience of our future forests.
Next Research Steps
The next phase of the project will explore how deer browsing and light conditions affect the understorey vegetation and key ecosystem functions – such as wood decomposition, soil microbial respiration, earthworm populations, and arthropod diversity.
Cooperation and Funding
The study involved researchers from the University of Würzburg, the German Centre for Integrative Biodiversity Research (iDiv) Halle–Jena–Leipzig, and the Universities of Göttingen, Oslo and Zurich.
The work was funded by the European Regional Development Fund (ERDF, project MainPro) and the German Research Foundation (DFG Research Unit BETA-FOR).
Prof. Dr Jörg Müller, University of Würzburg, Chair of Conservation Biology and Forest Ecology, Tel: +49 931 31-83378, E-mail: joerg.mueller@uni-wuerzburg.de
Ludwig Lettenmaier, Atle Mysterud, Oliver Mitesser, Christian Ammer, Torsten Hothorn, Simone Cesarz, Nico Eisenhauer, Daniel Kraus, Soumen Mallick, Jörg Müller, Kerstin Pierick: “Light and ungulate browsing interact in shaping future woody plant diversity through natural regeneration”; in Journal of Applied Ecology, 5 November 2025, doi: 10.1111/1365-2664.70211
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