A mixed forest is defined as a forest in which the main tree species does not exceed 75% of the growing stock. It may consist of coniferous trees (such as spruce or pine), broadleaved trees (such as birch), or a mixture of both. These kinds of forests are the environments where biodiversity prospers: especially broadleaved trees create vital habitats for many endangered species. Currently, broadleaves are a minority in boreal forests, which is why concrete actions are needed.
As a new endeavor, forestry operations in Finland have expanded their biodiversity programme with the plan to decrease the density of spruce seedlings. Unlike many other tree species, spruce thrives also in the shadow. This means that when planting density is reduced, the spruce seedlings will let in more sunlight and thus create better conditions for other natural tree species, such as pine and birch. Forests that consist of diverse tree species are also more adaptive to the changes and risks posed by climate change.
”The effects of climate change, such as drought and storm damages, are intensifying, and this poses a risk to forest health. By planting less spruce, we create better requisites for mixed-species forests that are more resilient. Quality seedlings from nurseries, together with natural seedlings, ensure that the forest becomes diverse and adaptive in the face of changing weather and nature conditions,” says Antti Rantanen, Forest Service Manager, Stora Enso Forest Finland.
Going forward with forest owners
In Finland, Stora Enso sources wood from forest owners and starts to offer the new spruce planting model for new forest service contracts. This means that the reduced spruce density will take place on planting sites from spring 2025 onwards. However, even though the density of spruce is reduced to 1,600, Stora Enso keeps planting at least 1,800 seedling plots per hectare in soil preparation to give room also for natural seedlings and ensure successful afforestation.
There are benefits for forest owners as well: since there are less seedlings and planting work, the forest owner can save costs. In later phases of forestry, mixed forests can be further enhanced in young stand management and thinnings. The PEFC and FSC certification criteria also encourage forest owners to preserve mixed forests.
“Mixed forest is one solution to the challenges of climate change and a concrete biodiversity action. From an economic point of view, preference of mixed forests is also about managing risks and ensuring return when forests remain strong and healthy,” Rantanen explains.
How about Sweden?
While the changes in spruce density concern Stora Enso’s biodiversity action programme in Finland, similar actions are taken forward to increase the share of broadleaved trees in Sweden as well. In Sweden, Stora Enso owns 1.4 million hectares of land (with 1.1 million hectares of forests) that provide the opportunity to pilot and make agile decisions for biodiversity.
“In our own forests, the long-term target is to increase the share of broadleaf-dominated forests on our land to 5%. We do this by identifying the areas where broadleaved trees will have the most impact and creating 1,000 hectares of broadleaved forests annually. We also have a set of actions to plant certain species ourselves, such as birch, and trail-plan temperate broadleaved seedlings,” summarizes Emma Wikström, Biodiversity Programme Manager, Stora Enso Forest Assets.
Whether talking about Finland, Sweden, or the global scale, mixed-species forests build a resilient, climate-proof asset for needed renewable materials, create vital habitats for various species, and thus support the health of the planet. This is why promoting diverse forests is an essential objective for forestry and remains one key focus area in Stora Enso.