Majestic and complex, lush and biodiverse: the way we think about primary and old-growth forests reflects their awe-inspiring presence in people’s collective imagination. In the same measure that they are distinctive and unique, these relatively undisturbed forests are also rare and rapidly disappearing in Europe. Currently, Europe’s primary and old-growth forests cover only an estimated 1% to 3% of the EU’s forest area, with 90% concentrated in just four countries: Sweden, Bulgaria, Finland and Romania.
Despite their small share, these rare forests are among the planet’s richest forest ecosystems. Globally, native and old-growth forests are on average 30% more abundant in species compared to tree plantations or restored forests and function as refuges for rare and endangered vegetation, animals and fungi, sustaining their populations and promoting their recovery. They also perform better in delivering a full range of ecosystem services compared to tree plantations, which deliver 61% lower soil erosion control and 13% lower water yield in comparison to reference native forests. The same principle holds true on the European continent, where unmanaged forests were shown to support higher biodiversity than comparable managed forests and to deliver important services to society such as regulating local weather regimes and hydrological resources.
What is more, due to their capacity to store carbon in their biomass, primary and old-growth forests help keep the worst effects of the climate crisis at bay, often storing more carbon than managed forests in similar biogeographical conditions. A new study found that old-growth temperate forests in the Dinaric Alps harbour the largest forest carbon stocks in Europe (507 Mg C ha−1 ), concentrated in a few large, ancient trees. Another study looking at primary beech forests in the Slovakian Carpathians found that aboveground biomass stocks were 20% greater in primary forests, and four times larger in deadwood mass stocks, compared to production forests. But this is not the only way such forests absorb and trap carbon, as much of it is also stored underground in the soil, as well as in the form of plant litter, lying and standing deadwood.
The aforementioned study in the Balkans revealed that, in the two old-growth forests analysed, composed of silver fir and beech trees, the proportion of carbon stored in living plants varied between 59-66%. Other 9–14% were stored in the form of dead biomass and 20–32% in soil down to 60 cm from the surface. These proportions may vary in other European old-growth forests, depending on forest composition, geographic location and study methodology.
Due to their impressive features, primary and old-growth forests also provide unique recreation opportunities, which are often acknowledged by tourism and hiking guides.
Previously critically endangered in Estonia, the bracket fungus Amylocystis lapponica, a specialist species for old-growth forests, saw its population recover thanks to expansion from a single forest reserve to other parts of Estonia’s network of protected forests. Photo: Caspar S / Wikimedia Commons
Protecting primary and old-growth forests is urgent and critical, as continued threats from logging and fragmentation mean these critically endangered ecosystems continue to disappear at an alarming rate. In Sweden, for instance, at least 19% of all-clear cuts since 2003 occurred in old forests, which may lead to their disappearance within 50 years if current forest conversion rates remain unabated.
As a large part of these forests is unmapped, and their precise locations are unknown, the European Commission committed to strictly protecting all the EU’s remaining primary and old-growth forests by 2030.
So what exactly classifies as an old-growth or primary forest? And how come mapping is still a challenge, given the amount of effort and technology employed in inventorying Europe’s forests?
Defining and identifying primary and old-growth forests
A common definition has been subject to extensive debate among scientific and policy-making communities. Firstly, because terms such as old-growth, primary, primaeval and virgin forests have often been used interchangeably, there is conceptual confusion. However, agreeing on a common terminology is not only relevant to science and research. An operational definition – which provides practical steps to measure or apply the term in research and inventorying – has implications for what counts as a primary or old-growth forest or not, and in turn, is decisive in defining a forest’s protection status. This is why adopting widely accepted definitions is necessary.
It is to this end that the Commission committed in its Forest Strategy for 2030 to develop, together with national experts, guidelines that would provide commonly accepted definitions and criteria for the identification and mapping of these forests.
The Hainich National Park, in Germany's state of Thuringia, is open to the public and is part of UNESCO's list of Ancient and Primeval Beech Forests of the Carpathians and Other Regions of Europe. Photo: Jens Fischer/Hainich National Park
The guidelines define primary forests on the basis of an existing definition by the Food and Agricultural Organisation (FAO): forests composed of native species, naturally regenerated, and where no clear, visible indications of human activities exist, meaning that natural ecological processes are not significantly disturbed. This definition includes, for instance, pristine untouched forests, as well as forest reserves managed for nature conservation and forests inhabited by indigenous peoples which fall within the aforementioned primary forest definition.
Old-growth forests are stands or areas which consist of native species and are characterised by natural structures and dynamics. They differ from primary forests in that they can also originate from planted or sown native tree species as long as, after several decades of natural development without significant intervention, they develop characteristics that resemble late developmental phases in primary forests. This definition, thus, does not exclude forests with signs of past low-intensity human activity.
Ensuring adequate protection is currently a challenge for both primary and old-growth forests, with many being logged even before they are identified as such. That is partially because, in many countries, forest inventories do not adequately identify or capture these ecosystems, leading to incomplete data on their location. However, the mapping of primary and old-growth forests does not automatically ensure their protection. A new study found significant increases in disturbance rates in mapped primary forests consistent with logging operations in many jurisdictions.
Estimates indicate that 93% of EU’s mapped primary and old-growth forests fall within the Natura 2000 network of protected areas and 87% are strictly protected. Yet, the protection status of the 2.9 million ha of potential (unverified) primary and old-growth forests, an extent greater than the mapped part, remains to be elucidated.
Decomposing tree trunk covered by moss and fungi in the Rajhenav primary forest in Kocevski Rog, Slovenia. The presence of deadwood and woody debris is one of the main characteristics of primary and old-growth forests. Photo: kato08/Adobe Stock
Supporting old-growth forest recovery
While mapping and protecting primary and old-growth forests is a conservation priority, in some countries, additional measures such as forest rewilding might need to be considered given the reduced extent of the remaining patches of primary and old-growth forests.
As previously mentioned, secondary forests, or forests affected by human disturbances, can develop old-growth characteristics, such as higher volumes of standing wood, large living trees, higher amounts of deadwood and woody debris, and canopy openings of various sizes – as long as they are not further affected by human action and forestry activities. Approaches fostering forest recovery and regeneration can help create buffer zones that limit the effects of disturbances on remaining fragmented patches of primary and old-growth forests. At the same time, protected buffer zones can support the recovery and recolonisation by old-growth specialist species. Establishing protected areas around primary forests and expanding old-growth zones around primary forest fragments, thus promoting connectivity and the development and dynamic of forest-dependent species, are essential to prevent further loss of some of Europe’s most precious forest ecosystems and the array of ecosystem services they provide.
Moreover, natural rewilding through natural forest expansion is already taking place all over the European continent and represents a low-cost approach to fostering forest biodiversity beyond primary and old-growth forests, in line with the new EU Nature Restoration Regulation. The effects of forest rewilding – a process initiated when forest or agricultural management is abandoned, letting nature do the job of repairing or reclaiming altered ecosystems – are studied in new EU-funded projects such as WILDCARD and wildE. Such scientific contributions will provide further references for ecological restoration by detailing ecosystem services under unmanaged conditions, such as benchmarks for carbon sinks harboured in different types of primary and old-growth forests.
This will add to existing evidence that already points, for instance, to significant carbon sequestration benefits of protecting, restoring and allowing continued growth of existing forests in Europe. A recent paper estimated this gain at 309 megatons of carbon dioxide equivalents per year – an amount higher than the current forest sink and comparable to the EU Green Deal carbon removal target. It is nevertheless important to highlight that the need to safeguard primary and old-growth forests does not imply a reduction in the delivery of provisioning services such as timber at the EU level or long-term carbon storage in wood products, as primary and old-growth forests represent at most only around 3% of the EU forest area. The question is rather how to foster management options at the landscape level aimed at nature restoration and conservation in synergy with the delivery of services such as wood and carbon sequestration and storage.
Video: Identifying old-growth forests – WILDCARD project