Dense, Dark Forests are a Modern Phenomenon

Below are artistic palaeo-reconstructions of ecosystem states in Central Europe over the last 23 million years. These illustrations depict typical landscapes and key large herbivores from six time periods. This thinking somewhat parallels recent conservation research and thinking from the Americas. 

The following is a summary of the full article, which can be found here. 

Dense, dark forests in Europe are a modern phenomenon

by Aarhus University

edited by Gaby Clark, reviewed by Robert Egan

For over 20 million years, the landscape of Europe has been a tree-rich mosaic of grasslands, scrubs and more or less open woodlands with an abundance of wildflowers. This is the conclusion of a new and comprehensive study of Europe's vegetation history—a study that suggests modern afforestation runs counter to the continent's long-term ecological trajectory.

Imagine that you are walking through pristine nature in central Europe 100,000—or even a million—years ago. If you picture a dark, dense primeval forest, where sunlight barely reaches the forest floor, then you have taken a wrong turn. Not geographically, but temporally.

But if you picture scattered woodlands combined with colorful flowery meadows, where lots of different birds and butterflies are thriving—you're probably on the right track.

From nature's perspective, the dense forests are a very recent phenomenon.

A new, comprehensive study led by Aarhus University shows that Europe's landscapes over the past more than 20 million years have predominantly been a mosaic: a mixture of grasslands, scrub and woodlands of varying density. Such a light-filled, flower-rich open woodland was shaped by grazing animals.

The study has been published in Biological Conservation.

"The study shows that current reforestation practices are on the wrong track—both here in Denmark, where subsidies are only granted for planting dense forests, and elsewhere in Europe. This 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 over millions of years," says Professor Jens-Christian Svenning from the Center for Ecological Dynamics in a Novel Biosphere (ECONOVO), Department of Biology at Aarhus University, senior author of the study.

Svenning adds, that the so-called "closed-forest paradigm" for decades has dominated nature management and our understanding of what is natural: the idea that dense forests with closed canopies were Europe's natural baseline before human intervention.

The new study takes a significant step beyond previous research. Whereas earlier studies have primarily focused on relatively recent periods in the past, the researchers here bring together all available paleoecological evidence covering the entire period from the Miocene epoch (which began around 23 million years ago) to the pre-industrial era.

The researchers reviewed paleoecological studies covering the last 23 million years based on pollen records, plant macrofossils, charcoal particles from ancient fires, stable-isotope analyses of herbivore teeth and bones, fossil insects and mammals, and ancient environmental DNA preserved in sediments.

The conclusion is clear: across this long period, the typical landscape was a dynamic tree- and flower-rich mosaic, where large wild herbivores such as elephants, rhinoceroses, aurochs and bison kept vegetation semi-open and diverse—and this was the case in temperate climates similar to those prevalent in Europe today, as well as in warmer and in cooler climates.

The ecosystems we see in Europe today lack the large wild herbivores that not only shaped landscapes but also sustained its biodiversity for millions of years. The most dramatic shift has largely taken place within the last hundred years, when traditional extensive grazing disappeared from large parts of the landscape.

This suggests that the sharp division between "forest" and "open habitats" that characterizes modern conservation practice is a modern invention.

Implications for afforestation and restoration

The findings have direct implications for nature management and biodiversity across temperate Europe—precisely at a time when forests are being planted in the name of climate mitigation and biodiversity.

If the goal is to restore ecosystems resembling those in which Europe's species evolved and are still adapted to, the study indicates that uniform, dense forests are not the answer.

"Instead, restoration efforts should place greater emphasis on creating and maintaining mosaics of woodland and open habitats—not least through the restoration of natural-living large herbivores," Svenning concludes.

The study thus reinforces growing evidence from earlier research: Europe's past was lighter, more heterogeneous and more strongly shaped by large animals than we have long assumed.

End of article summary.

Comment on this blog post

A great deal of North American conservation is based on restoring fire to landscapes that were long burned by lightning and Native Americans. Burns go a long way toward restoring landscapes that have much in common with those discussed above. Although not mentioned in the article, burning was also a major factor in Europe until recently. (See Vestal Fire by Steven Pyne.) The above article reminds us that restoring another major factor, large grazers, is also being being researched as a part of biodiversity conservation in such North America sites as Nachusa Grasslands. But one key factor for both continents is that the "leave nature alone" approach does not work for biodiversity conservation in many areas.