Retention trees are burned, and controlled burning of forest is carried out because, thanks to effective fire protection, there are not many natural forest fire sites in Finland. This means that many species that depend on burnt wood have become rare or endangered. Burning retention tree groups creates small fire environments that benefit species dependant on burnt down forest areas. Fires accelerate the formation of decayed wood, which also benefits species other than fire-dependant ones.
Groups of retention trees have been burned as part of the Metsä Group Plus forest management model since 2024. Under this forest management model developed by Metsä Group, some of the retention tree groups left on felling sites are burned in a controlled and planned manner. Retention trees are trees preserved during forest management. Under the Metsä Group Plus forest management model, 30 retention trees and 10 biodiversity stumps are left standing per hectare, which is more than the established practices.
“The burning of retention trees is one tangible measure of regenerative forestry embraced by Metsä Group to advance its goal of improving the state of forest nature by 2030. Burning retention tree groups is a cost-effective and safe way to create small-scale fire habitats in forests for species that need them. We will continue to burn groups of retention trees in the coming years for the benefit of forest nature around Finland,” says Silja Pitkänen-Arte, Sustainability Manager at Metsä Group's Wood Supply and Forest Services.
Burnt wood is needed by a large group of insects, and the first head to the fire site within a few hours after the fire. The insects found in the burned retention tree groups can show very rapid effects on species, which has been observed on the monitoring sites established by Metsä Group in south-eastern Finland. For example, in Taipalsaari, several rare insect species were found in the 2025 follow-up surveys at a site that was burned in the summer of 2024, including the endangered species Drapetes mordelloides and Chrysis equestris. The wood decaying process that starts as a result of a fire also has long-term positive effects on the species in the area.
The burning of retention trees is already taken into account when the felling of a site is planned. The location of retention tree groups to be burned is planned to ensure safety. The area is prepared in connection with soil preparation. Crown wood is piled under the trees to be burned to boost burning. A firebreak is dug around the site with an excavator, and the supply of fire water is ensured.