A study led by the University of Jyväskylä in Finland has identified a key ecological limit for clearcutting in boreal forests. This is the first time such a threshold has been established for maintaining bird species that depend on old-growth forests. The research suggests that to preserve these species, either the average time between logging cycles should be at least 90 years, or about 20% of the forest area should be protected from clearcutting. These findings offer a measurable guideline for managing forests in an ecologically sustainable way. Clearcutting, the practice of removing all trees from a large area, is widely used in boreal forests, which are found in northern regions of the world. While it is a common forestry technique, it has been linked to declines in forest biodiversity. Although the immediate effects of logging are well-documented, the long-term and cumulative impacts on ecosystems, especially at a landscape level, have been less clear. To address this, researchers analyzed bird-monitoring data from Finland between 2006 and 2020, along with maps showing the accumulation of clearcut areas across Europe. The study, published in the Journal of Applied Ecology, found that in areas where large amounts of clearcutting had occurred over 20 years, populations of both common and old-growth forest-dependent birds were lower. Senior Researcher Rémi Duflot from the University of Jyväskylä summarized the findings, noting the negative impact of prolonged clearcutting on forest bird populations. A major outcome of the study was the identification of a "safe operating space" for forest ecosystems. The researchers found that to maintain stable or recovering populations of old-growth forest birds, clearcutting should not exceed about 10% of the forest area over a 10-year period. This could be achieved either by extending the time between logging cycles to about 90 years or by protecting roughly one-fifth of the forest from clearcutting. Duflot explained that these measures would help ensure the long-term survival of forest bird species. The researchers caution that these thresholds might vary depending on the region and the species involved. For example, some organisms like lichens and mosses may require even more undisturbed habitat than birds. Therefore, they recommend that further studies on different species groups are needed before setting universal guidelines. The findings, however, provide a practical tool for decision-makers, forest owners, and the forestry sector to plan sustainable forest use that balances economic needs with biodiversity conservation. Professor Mikko Mönkkönen, an expert in applied ecology, emphasized that the method used in the study is adaptable and could be applied globally to help protect forest ecosystems.