In 2023, a research group from Aarhus University in Denmark found that light woodland and open vegetation dominated Europe’s temperate forests before Homo sapiens.
In a new study, recently published in Journal of Ecology, they take a closer look at the composition of these forests.
The results show that European wildwoods were rich in hazel, oak, and yew — species thriving in dynamic semi-open ecosystems rather than in classic dense forests.
“Often, we imagine established forests as dense, closed spaces where light-demanding species like oak and short-statured species like hazel and yew were rare. Our results challenge this view, showing that oak, hazel, and yew consistently thrived in these ancient woodlands, further supporting a picture of a semi-open, mosaic-like vegetation,” explains Dr Elena Pearce, lead author and postdoc at the DNRF Center for Ecological Dynamics in a Novel Biosphere (ECONOVO), Department of Biology, Aarhus University.
Plants as detectives
The team looked to oak, hazel, and yew as “detectives” of ancient forest life, revealing clues about how past woodlands were structured.
For instance, hazel shows stronger pollen and flower production in sunlit areas, oak resprouts vigorously after browsing, and yew, while somewhat shade-tolerant, requires semi-open conditions to avoid competition from taller trees. In fact, all three taxa tend to decline in tall, shady forests. Yew is also extremely sensitive to fire but can coexist with large megafauna species such as horses, oxen, or likely even larger animals, due to its high toxicity, which deters extensive browsing.
Large herbivores as nature’s landscape architects
The researchers used the REVEALS model for pollen-based reconstructions to analyse the prevalence of oak, hazel, and yew in two key periods: the Last Interglacial (129,000-116,000 years ago) and the early-to-mid Holocene (8700-5700 years ago). See fact box.
By further investigating forest composition, they revealed that open and semi-open vegetation supported diverse species combinations that would have struggled in closed-canopy environments.
Rather than natural fires or climate regimes causing openness, these new results suggest that large herbivores played a leading role in maintaining open and semi-open landscapes. Yew’s sensitivity to fire highlights this, as it would have struggled to thrive in fire-prone systems yet persisted in ancient woodlands where herbivores likely kept forests dynamic and open.
“These species tell us that ancient forests were not uniformly dominated by tall shade-giving trees but must have been composed by a dynamic mix of open, semi-open and closed areas, providing a high diversity of habitats,” says Professor Jens-Christian Svenning, senior author and director of ECONOVO.
Modern nature management inspired by the past
The implications go beyond historical ecology. Semi-open woodlands may have played a critical role in Europe’s biodiversity, creating habitats for species adapted to a variety of conditions.
“Our findings provide a new perspective on ancient ecosystems and highlight the need to maintain semi-open woodlands today. These environments support a diverse mix of plants and animals, and understanding them can help to inform rewilding efforts,” says Dr Pearce.
The study also highlights how open, dynamic woodlands might contribute to climate resilience and biodiversity gains.
“As we face global challenges like warming temperatures, climatic extreme events and rising tree pest invasions, creating dynamic, varied woodland mosaics is likely to provide more robust ecosystems functions and biodiversity benefits than conventional dense forest plantings,” says Professor Svenning.
Semi-open forests allow for diverse plant species, which in turn provide essential functions like carbon storage, pollinator habitats, and broader biodiversity maintenance. Reforestation strategies that recreate these semi-open, dynamic woodland structures likely better align with future climatic and ecological challenges, guiding sustainable forest management in Europe and beyond.