An international research group has published a comprehensive review that provides science-based indicators for identifying old-growth forests in Northern Europe. The publication is intended to provide cross-border support for policymakers and authorities implementing the European Commission’s requirement to identify and protect the remaining primary and old-growth forests.

Old-growth forests are some of Europe’s most valuable natural ecosystems, but they are also among the most threatened. Their role in conserving biodiversity, regulating the climate, preserving cultural heritage and supporting people’s wellbeing is invaluable.According to a rough estimate, only around three per cent of Europe’s forests meet the criteria for primary or old-growth forests, and their extent continues to decline rapidly also in Northern Europe.

The importance of old-growth forests for biodiversity is linked to their structural diversity and the ecological processes that have developed over long periods of time. Dead and old trees, as well as deadwood, provide habitats for many species. Fungi, lichens, mosses, deadwood-dependent insects and many cavity-nesters are particularly reliant on the conditions typical of old-growth forests.

In naturally developed boreal forests, tree stand structure can vary considerably. Younger trees may make up a large part of the canopy, even where the forest also contains many old trees and shows ecological processes characteristic of old-growth forests.

“In Finland, the mandatory criteria for old-growth forests set by the Government emphasise the average age of the dominant tree stand and the total volume of deadwood per hectare,” says Mikko Mönkkönen, professor of applied ecology at the University of Jyväskylä. “These criteria alone are not particularly effective for identifying old-growth forests. Deadwood volume varies considerably between forest types and geographical zones, as well as according to the forest’s disturbance history, making it difficult to establish precise volume thresholds. The key to identifying old-growth forests is to view the forest as a whole and consider the overall picture formed from a range of characteristics.”

EU requires Member States to identify old-growth forests

The EU Biodiversity Strategy for 2030 and the EU Forest Strategy for 2030 require Member States to define, map and strictly protect all remaining primary and old-growth forests. The Renewable Energy Directive (RED III) also prohibits logging in such forests. The EU Restoration Regulation does not explicitly mention old-growth and primary forests, but it prohibits the deterioration of habitat types in good condition as defined in the Habitats Directive. The criteria for old-growth forests proposed by the research group help to assess the condition of forest habitats.

According to the European Commission’s guidelines, a forest stand is considered an old-growth forest if it meets all three main indicators and at least two of the four complementary indicators. Three main indicators to be considered are native tree species, dead wood and old trees, while complementary indicators are natural regeneration, structural diversity, habitat trees and indicator species. The research group’s review provides scientifically grounded recommendations on how these indicators should be applied in practice in the boreal and hemiboreal forests of Northern Europe.

Key recommendations from researchers

When an old-growth forest is viewed as an ecological whole, a range of factors are taken into account, including native tree species, the age and structure of the tree stand, the amount and quality of deadwood, habitat trees, and species characteristic of old-growth forests. A minimum area of 0.5 hectares is proposed for the assessment of a forest stand, a threshold commonly used internationally.

• Native tree species: tree species naturally occurring in the area and dominant in the stand.
• Deadwood: at least 5% of the total growing stock volume, with a diverse range of decay stages.
• Old trees: at least 20 old trees per hectare, with the age threshold varying according to forest type and zone.
• In addition, natural regeneration, structural diversity, habitat trees (e.g., trees with cavities and standing dead trees), and regional old-growth forest indicator species are assessed.

Precautionary principle protects valuable forests

Overly strict or unscientific national criteria could leave a large proportion of the remaining old-growth forests unprotected and vulnerable to logging. Underestimating the extent of remaining old-growth forests can result in long-term biodiversity losses and increase the costs of future restoration efforts.

There is inevitably some uncertainty in identifying old-growth forests. Natural variation between forests is considerable, field measurements are limited, and different indicators can produce different results. For this reason, the researchers recommend applying the precautionary principle: borderline cases should not automatically be excluded from consideration. Instead, their ecological value should be assessed more carefully.

“Even small old-growth forests can be important for threatened species,” says Kimmo Syrjänen, project manager at the Finnish Environment Institute. “In Southern Finland, the few remaining sites are small and fragmented. Most unprotected old-growth forests are located in Northern Finland, particularly on state-owned land in Upper Lapland, within the Sámi Homeland.”

A common scientific basis supports decision-making

The indicators and thresholds used to identify old-growth forests are interpretations of scientific knowledge and may be challenged for political or economic reasons. A transparent, scientifically sound approach based on the precautionary principle is therefore essential to avoid a decline in forest biodiversity, societal conflict, and legal problems.

“The indicators we recommend bring consistency and transparency to the identification of old-growth forests in northern Europe,” says Raisa Mäkipää, research professor at the Natural Resources Institute Finland. “The indicators provide a solid basis for buyers of timber and wood-based products to assess sustainability. Timber procurement by the forest industry requires a predictable operating environment, and protecting forests that meet the established criteria would improve predictability.”

Mikko Mönkkönen and Bengt-Gunnar Jonsson will present the study to the press and other interested parties on 29 September from 13:30 to 15:30 (CET) in Brussels. They will be joined for a discussion on the study’s impacts and policy recommendations by Acting Director Ion Codescu (DG Environment, European Commission), Forest Director Marko Mäki-Hakola, Copa-Cogeca (Central Union of Agricultural Producers and Forest Owners) and Member of the European Parliament Katri Kulmuni. The event can also be followed online.

Read more information about the event: https://fortran.fi/europes-old-growth-forests-are-national-definitions-keeping-pace-with-science/

Link to the policy recommendation: https://jyx.jyu.fi/jyx/Record/jyx_123456789_113643

Link to the article: https://link.springer.com/article/10.1007/s13280-026-02457-0

The study was conducted by researchers from the University of Jyväskylä (Finland), Vytautas Magnus University (Lithuania), the University of Latvia, Mid Sweden University, the Swedish University of Agricultural Sciences (SLU), the University of Tartu (Estonia), the Natural Resources Institute Finland (Luke), and the Finnish Environment Institute (Syke).

The work was funded by the Strategic Research Council (STN ForTran project), which operates in conjunction with the Research Council of Finland, and by the Estonian Research Council.

Wisdom Letters is an interdisciplinary, peer-reviewed, open-access journal focusing on sustainability transitions and planetary well-being. The articles are based on high quality scientific research and provide policy recommendations that can be used in policymaking, education and civil society. Wisdom Letters is produced by the University of Jyväskylä School of Resource Wisdom JYU.Wisdom.