Challenging the Closed-Forest Paradigm in European Ecology

New paleoecological research from Aarhus University reveals that the dense, dark forests dominating much of Europe today are not the ancient norm but a relatively recent development. For over 23 million years—from the Miocene epoch through the pre-industrial era—Europe's temperate landscapes were characterized by dynamic mosaics of open grasslands, scrublands, scattered woodlands, and light-filled savannas. These heterogeneous environments, teeming with wildflowers and light-demanding species, were primarily shaped and maintained by large wild herbivores acting as ecosystem engineers.

This discovery challenges the 'closed-forest paradigm' that has guided conservation and forestry policies for decades, assuming uniform, shaded woodlands as the baseline for restoration. Instead, the study argues that true ecological fidelity requires embracing Europe's evolutionary heritage of openness and diversity, with profound implications for biodiversity, climate adaptation, and land management across the continent.

The Aarhus University Study: Methods and Multi-Proxy Approach

Led by Ph.D. student Szymon Czyżewski and senior author Professor Jens-Christian Svenning at Aarhus University's Center for Ecological Dynamics in a Novel Biosphere (ECONOVO), the research synthesizes an unprecedented breadth of paleoecological data spanning 23 million years. Published in Biological Conservation (DOI: 10.1016/j.biocon.2026.111749), it integrates multiple independent proxies to reconstruct vegetation structure with high confidence.

Key methods include fossil pollen records, which indicate plant communities but not canopy closure; plant macrofossils providing direct evidence of light-demanding species; charcoal particles revealing frequent fires that prevented dense overgrowth; stable isotope analyses from herbivore teeth and bones showing diets dominated by C3/C4 grasses typical of open landscapes; fossil insects and mammals adapted to grasslands and savannas; and ancient environmental DNA (eDNA) from sediments confirming mosaic habitats. As Czyżewski notes, 'Each type of proxy offers its own perspective, but together they let us see whether the landscapes were covered by dense forests, open grasslands, or a mix of the two.'

This rigorous, convergent evidence debunks single-proxy limitations, painting a consistent picture of herbivory-driven openness.

Deep-Time Perspectives: Miocene to Pleistocene Mosaics

Tracing back to the Miocene (23–5.3 million years ago), Europe's flora and fauna evolved in tree-rich but open systems. Pollen data shows abundant grasses and herbs alongside trees, while macrofossils reveal flowers and light-loving plants incompatible with shaded understories. Large herbivores—elephants, rhinos, mega-horses, and early bovids—browsed saplings, trampled vegetation, created wallows, and promoted fires, fostering patches of scrub, parklands, and meadows amid scattered woodlands.

During the Pleistocene (2.6 million–11,700 years ago), including ice ages and interglacials, this mosaic persisted. Even in warmer interglacials like the Eemian (130,000–115,000 years ago), pollen reconstructions indicate 50–75% open or semi-open cover, not uniform forest. Megafauna biomass was high, with grazers outnumbering browsers, as dental microwear and isotopes confirm open-diet reliance. Fossil assemblages feature insects and mammals thriving in heterogeneous light environments, underscoring stability across climatic swings.

Holocene Transitions: Human Influence and Megafauna Collapse

The Holocene (11,700 years ago–present) marks increasing human interplay. Post-Late Pleistocene megafaunal extinction (~12,000 years ago), tree cover expanded under reduced browsing, but Mesolithic hunter-gatherers maintained openness via burning and hunting. Neolithic farming (~8,000 years ago) introduced domestic livestock, partially mimicking wild herbivory, sustaining mosaics through extensive grazing.

Mid-Holocene pollen peaks show ~70–80% tree cover continent-wide, yet proxies reveal non-closed canopies: abundant heliophilous (light-loving) taxa, fire signals, and grazer isotopes. Medieval overexploitation opened landscapes further, but 19th–20th century agricultural intensification and grazing decline allowed canopy closure, birthing today's dense forests—often monocultures resembling production stands more than wild systems.

The Modern Shift: Why Dense Forests Emerged Recently

The tipping point came in the last century: wild herbivore extirpation completed millennia ago, but traditional free-roaming livestock vanished with industrialization. Europe's forests now cover ~40% of land, but shaded understories suppress biodiversity. Svenning explains, 'The most dramatic shift has largely taken place within the last hundred years, when traditional extensive grazing disappeared.' This novel state lacks evolutionary analogues, vulnerable to pests, storms, and climate shifts.

Pollen biases historically overstated closure; corrected models (e.g., REVEALS) confirm ~60% humid temperate openness pre-humans.

Biodiversity Hotspots in Mosaic Landscapes

Europe's flora and fauna evolved in light-rich mosaics: skylarks, jackdaws, hamsters, and poppies trace to herbivore-disturbed openings. Forest plants prefer semi-open conditions; dense canopies favor invasives and shade-tolerants. Studies show 23% land gained tree connectivity recently, slashing heterogeneity and capacity for open-adapted species.

• Light-demanding herbs thrive in grazed gaps, boosting pollinators.
• Birds like woodlarks need edge habitats.
• Mammals such as hares require grassy patches.

Uniform forests risk 'green deserts,' losing 10% biodiversity hotspots yearly despite EU carbon stores of 15 Gt.Explore research roles advancing forest biodiversity.

Policy Critiques: Afforestation on the Wrong Track

EU Green Deal targets 3 billion trees by 2030, but subsidies (e.g., Denmark's conifer grants, Germany's beech focus) prioritize dense stands, ignoring paleo-baselines. Svenning warns, 'Current reforestation practices... will not only be harmful for biodiversity; it will be in direct contradiction to the type of ecosystems that Europe's species have evolved in.' Monocultures amplify disturbance risks, as warming doubles forest impacts by 2100.

Rewilding Europe critiques uniform planting; closer-to-nature subsidies needed for resilience.

Rewilding Solutions: Restoring Herbivores and Mosaics

Solutions lie in trophic rewilding: reintroduce bison, wild horses, tauros cattle. Examples include Rewilding Europe's Dutch/Croatian projects, where grazers create patches, boosting birds/butterflies. Aarhus advocates gradual introductions, monitoring via pollen/eDNA. 'Restoration efforts should place greater emphasis on creating and maintaining mosaics... through the restoration of natural-living large herbivores,' per Svenning.

France's Loire Valley grazing maintains savannas; align with EU Biodiversity Strategy for heterogeneous futures.Higher ed opportunities in European ecology.

Climate Change and Future Forest Dynamics

With disturbances (fire, pests) projected to double, mosaics offer resilience—open patches limit spread, herbivores reduce fuel. Dense stands risk collapse; paleo-mosaics buffered past shifts. Policymakers must integrate baselines into carbon strategies, balancing sinks with diversity.

Expert Perspectives and Aarhus University's Role

Svenning's ECONOVO pioneers novel biosphere dynamics; team integrates paleoecology with modern ecology. Czyżewski's synthesis sets new standards. Ties to global rewilding debates, urging policy pivots.Phys.org coverage.

Photo by Jakub Pabis on Unsplash

Outlook: Toward a Mosaic Europe

This research reframes restoration: from 'primeval forest' myths to evidence-based mosaics. For academics eyeing research assistant jobs, paleoecology thrives. Explore Rate My Professor for Aarhus faculty or higher ed jobs in conservation. Career advice for ecologists; university jobs abound. Post jobs at /post-a-job.