Dense, Dark Forests in Europe: A Modern Phenomenon, New Biological Conservation Study Reveals

Discovering Europe's Ancient Mosaic Landscapes

The latest research from Aarhus University challenges long-held assumptions about the natural state of European forests. For decades, scientists envisioned a primeval landscape dominated by thick, shadowy woodlands stretching across the continent. However, a comprehensive analysis reveals that dense, closed-canopy forests represent a departure from the norm, emerging only recently in geological terms.

Lead author Szymon Czyżewski, a PhD student at the Center for Ecological Dynamics in a Novel Biosphere (ECONOVO), along with senior author Professor Jens-Christian Svenning, synthesized evidence spanning 23 million years—from the Miocene epoch to the pre-industrial period. This work, published in the journal Biological Conservation, paints a picture of dynamic, light-filled environments teeming with life.

Unpacking the Paleoecological Methods

To reconstruct these ancient ecosystems, the researchers drew on multiple proxies, ensuring a robust, multi-faceted view. Fossil pollen records provided snapshots of plant communities, while plant macrofossils offered direct evidence of species presence. Charcoal particles indicated fire regimes that prevented canopy closure, and stable isotope analyses from herbivore teeth and bones revealed dietary habits pointing to open grazing lands.

Fossil insects and mammals further corroborated the openness, with species adapted to grasslands and savannas dominating. Ancient environmental DNA (eDNA) from sediments added genetic confirmation of this mosaic. By integrating these lines of evidence, the team achieved unprecedented confidence in their timeline, far surpassing single-proxy studies.

"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," explains Czyżewski.

A Tree-Rich Mosaic Over Millions of Years

From 23 million years ago through various climatic shifts—including warmer periods and ice ages—Europe's temperate zones featured heterogeneous landscapes. Tree cover existed but in scattered, open formations interspersed with grasslands and shrubs. Wildflowers bloomed abundantly, supporting diverse pollinators and insects.

This configuration persisted even in climates akin to today's, contradicting the 'closed-forest paradigm' that posits uniform dense woods as the baseline. Instead, the continent resembled modern savannas or parklands, with light penetrating to the forest floor and fostering understory diversity.

Evidence from the Miocene shows early examples, evolving through the Pliocene and Pleistocene, always maintained by ecological processes rather than human hands.

The Pivotal Role of Megaherbivores

Central to this stability were large herbivores—elephants, rhinos, aurochs (wild cattle), bison, and mega-horses. These 'ecosystem engineers' browsed trees, trampled saplings, and created gaps through grazing and wallowing. Fires, fueled by their activities, further opened canopies.

Stable isotope data from teeth confirm C3/C4 grass diets, indicating vast open areas. Fossil assemblages include grazers outnumbered browsers, underscoring openness. Svenning notes, "Large wild herbivores... kept vegetation semi-open and diverse."

Without them, as in modern Europe, vegetation densifies, altering habitats profoundly.

The Modern Shift to Density

Dense forests proliferated post-Megafaunal extinction around 12,000 years ago, accelerated by Neolithic farming and Medieval overexploitation followed by abandonment. The last century's decline in extensive grazing cemented this change.

Today, Europe's forests cover about 40% of land, but many are monocultures or overly shaded plantations. This mismatches species' evolutionary history, leading to biodiversity loss.

Photo by Datingscout on Unsplash

Biodiversity Adapted to Openness

Species like Eurasian skylarks, western jackdaws, and European hamsters—now tied to farmlands—evolved in these mosaics. Forest understory plants and poppies thrived in light gaps created by herbivores.

Dense canopies suppress these, favoring shade-tolerant invasives. The study urges rethinking conservation's forest-vs-open divide.

In Denmark, subsidies prioritize conifer monocultures, exacerbating homogenization.

Reforestation Challenges Across Europe

EU Green Deal aims for 3 billion trees by 2030, but uniform planting risks 'green deserts.' Denmark's policies exemplify: grants only for dense stands, ignoring paleo-baseline.

Germany and UK face similar issues, with beech dominance shading natives. Statistics: EU forests store 15 Gt carbon but lose 10% biodiversity hotspots yearly.

• Carbon focus overlooks habitat diversity
• Monocultures vulnerable to pests/climate
• Missing herbivores perpetuates closure

Solutions: Diverse mosaics enhance resilience.

Case Studies: Denmark and Beyond

In Denmark, subsidies drive spruce plantations, mimicking production forests not natives. Aarhus researchers advocate policy shift.

UK's ancient woodlands, post-elm decline, show openness historically. Rewilding Europe project in Netherlands/Croatia reintroduces grazers successfully.

France's Loire Valley: Grazing maintains savannas.

Rewilding as the Path Forward

Restore megaherbivores: European bison, wild horses, tauros cattle. Projects prove increased biodiversity, carbon storage via deep roots.

Step-by-step: Assess sites, introduce grazers gradually, monitor pollen/veg changes. Aligns with EU Biodiversity Strategy.

"Restoration efforts should... mosaics of woodland and open habitats," Svenning urges.

Implications for Policy and Research

Revise subsidies for mosaic planting. Integrate paleo-data into models.

Higher ed opportunities abound: Paleoecology roles at AcademicJobs.com/research-jobs, Aarhus-like centers. Explore higher-ed-jobs in ecology.

Photo by Jakub Pabis on Unsplash

Future Outlook: Balancing Climate and Nature

Open mosaics store carbon deeply, resist extremes. With rewilding, Europe can meet net-zero while boosting species.

Stakeholders: Policymakers, NGOs, universities collaborate. Actionable: Pilot herbivore reintroductions, track via eDNA.

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