From guidelines to practice: Operational criteria for identifying old-growth forests in northern Europe

This paper proposes science-based operational criteria and specific thresholds for the three main indicators (native species, deadwood, and large/old trees) to effectively identify and protect old-growth forests in northern Europe, ensuring compliance with EU Biodiversity and Forest Strategies while minimizing misclassification.

The Gist

Imagine the forests of Northern Europe as a vast, ancient library. Most of the books in this library have been rewritten, edited, and reorganized by humans over the years. However, a tiny, precious collection—only about 3% of the total shelves—contains the original, untouched manuscripts known as "primary" and "old-growth" forests. These are the library's most valuable treasures, packed with unique stories (biodiversity) and essential services that keep the whole building running.

The European Union has issued a strict rule: these original manuscripts must be locked away and protected. But here's the problem: the librarians (forest managers) have a vague description of what an "original manuscript" looks like, but they lack a clear checklist to find them. Without a specific guide, they might accidentally lock up a modern book or, worse, leave the real treasure out in the open.

This paper acts as a new, detailed checklist to help librarians spot these ancient forests accurately. It translates the European Commission's broad ideas into a practical "spot-the-difference" game using three main clues:

1. The Native Cast: The forest must be populated mostly by the "original actors" (native tree species), not the new ones brought in from elsewhere.
2. The Fallen Props: There needs to be a pile of "fallen props" (deadwood) on the forest floor. The paper suggests that at least 5% of the total wood volume should be dead and decaying. Think of this as the forest's natural recycling bin, which is essential for its health.
3. The Elderly Stars: You need to see a crowd of "elderly stars" (large, old trees). The rule of thumb is to find at least 20 of these giants in every single hectare (about the size of two football fields).

The paper also suggests looking at the "supporting cast," such as how new trees are growing (regeneration), the complex layers of the forest, and special little homes for insects (microhabitats). However, the authors warn that you can't just look at one clue in isolation. It's like trying to identify a famous movie by only looking at the director's name; you need to check the cast, the script, and the set design all together to be sure.

By using these specific numbers and rules, the paper aims to stop the confusion. It ensures that the right forests get the strict protection they deserve without wasting time and money on forests that don't quite fit the bill.

Technical Summary

Technical Summary: From Guidelines to Practice: Operational Criteria for Identifying Old-Growth Forests in Northern Europe

Problem Statement
Primary and old-growth forests are critical for biodiversity, ecosystem services, and cultural value. However, the EU Biodiversity Strategy and the EU Forest Strategy for 2030 face a significant implementation gap: while these strategies mandate the strict protection of remaining primary and old-growth forests, these areas constitute only approximately 3% of the total EU forest area and remain highly threatened. Although the European Commission has established guidelines defining old-growth forests through three main indicators (native tree species, deadwood, and large/old trees) supported by five complementary indicators, there is currently a lack of science-based operational criteria and thresholds specifically tailored for boreal and hemiboreal forests in northern Europe. Without these specific criteria, the implementation of EU legal standards for identification and protection is hindered, risking misclassification and inefficient conservation efforts.

Methodology
The paper addresses this gap by translating the European Commission's broad indicators into concrete, science-based operational criteria and thresholds suitable for the northern European context. The authors focus on developing a framework that minimizes misclassification while ensuring cost-effective conservation. Rather than proposing new experimental protocols or future applications, the work synthesizes existing scientific knowledge to define specific quantitative limits and qualitative guidance for the three main indicators and five complementary indicators. The approach emphasizes the collective application of all indicators rather than relying on single metrics in isolation.

Key Contributions and Results
The primary contribution of this work is the provision of specific, actionable thresholds for identifying old-growth forests in northern Europe. The paper establishes the following key quantitative criteria:

• Native Tree Species: A requirement for native species dominance.
• Deadwood: A threshold of greater than or equal to 5% of the total wood volume.
• Large/Old Trees: A density of greater than or equal to 20 large or old trees per hectare.

In addition to these core thresholds, the paper offers detailed guidance on the assessment of regeneration patterns, structural complexity, microhabitats, and indicator species. The results underscore that these indicators must be applied collectively to accurately identify old-growth stands, ensuring that the definition is robust and scientifically defensible.

Significance
The significance of this paper lies in its role as a bridge between high-level policy guidelines and on-the-ground practice. By providing science-based operational criteria that meet EU legal standards, the work enables the consistent and accurate identification of the remaining 3% of primary and old-growth forests in the EU. This clarity is essential for minimizing misclassification errors and facilitating cost-effective conservation strategies, thereby supporting the successful implementation of the EU Biodiversity and Forest Strategies for 2030 in northern Europe.