Roe deer are significantly limiting the natural regeneration of tree species in deciduous forests, even in areas with abundant sunlight, according to new research from Julius-Maximilians-Universität Würzburg.
Published in the Journal of Applied Ecology, the multi-year study reveals that deer browsing can override the positive effects of light exposure in forest gaps, undermining efforts to increase species diversity and climate resilience. “We found that the impact of roe deer is particularly pronounced in these lighter areas,” said Ludwig Lettenmaier, a doctoral researcher at the university.
The research team, led by Professor Jörg Müller, conducted a four-year field experiment in the Würzburg University Forest, comparing fenced and unfenced plots in both open canopy gaps and shaded forest stands. Each plot measured 36 square meters and was monitored for tree regeneration.
“The additional light could not offset the negative influence of the deer on the unfenced plots,” Lettenmaier said. “Tree-species diversity was similar to that in the shaded areas.”
The study found that while a wide range of species initially emerged at heights below 1.3 meters—the typical browsing range for roe deer—only a few managed to grow beyond that vulnerable zone. As a result, tree-species diversity was effectively halved, regardless of light availability. “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,” said Müller, professor of conservation biology and forest ecology.
The findings have broad implications for forest management, particularly in regions with high deer populations. The researchers warn that selective browsing leads to a homogenization of forest regeneration, potentially reducing long-term ecosystem resilience.
The next phase of the project will examine how deer browsing and light conditions influence understory vegetation and key ecological processes, including wood decomposition, soil microbial activity, and invertebrate diversity.
Please note that the study, titled ‘Light and ungulate browsing interact in shaping future woody plant diversity through natural regeneration,’ is available in the Journal of Applied Ecology (DOI: 10.1111/1365-2664.70211).
