A study carried out in 2021 found that significantly more species inhabit high biodiversity stumps than regular logging stumps. In addition, all the discriminating species found in the study inhabited biodiversity stumps.
"In the study, I analysed regular logging stumps and high biodiversity stumps in the same areas. Significantly more species inhabited the diversity stumps than the regular stumps. In addition, many species were found in the biodiversity stumps that were not found in the regular logging stumps," says Juha Siitonen, a researcher at Natural Resources Institute Finland, who carried out the study.
The importance of high biodiversity stumps for forest species cannot be proved without a comparison with conditions in which no high stumps remain. The species found in biodiversity stumps were therefore compared with those found in regular logging stands. The species found in the regular logging stumps were present in the forest even without biodiversity stumps.
"It's worth the effort to make biodiversity stumps, because they increase the number of species dependent on decaying wood in the forest. About a third of the species were found only in biodiversity stumps. In addition, all the discriminating species found in the study were found in biodiversity stumps, which means they improve the survival of rare species in commercial forests," says Siitonen.
A total of four beetle species was found in the biodiversity stumps that were previously endangered, but whose situation has since improved.
Biodiversity stumps increase the amount of decaying wood
"A biodiversity stump is a tree trunk that has been cut at a height of a few metres during felling. We make biodiversity stumps during felling to increase the amount of vertical decaying wood in the forest, which is important for many forest species, as this study shows," says Vesa Junnikkala, Metsä Group's Director of Sustainability.
Metsä Group started to leave two high biodiversity stumps per hectare in 2016. At the beginning of 2020, this was increased to four. Biodiversity stumps are made, no matter which logging method is used. Making biodiversity stumps is voluntary for forest owners. Last year, the forest owner decided to leave high biodiversity stumps in the forest in 88 per cent of wood sales.
One of Metsä Group's 2030 sustainable objectives is to increase the amount of decaying wood in forests. Leaving high stumps is one means to this end. Other means include leaving retention trees and sparing existing dead wood during forestry operations.
Metsä Group commissioned a study of biodiversity stumps, because there is currently little published research on the contribution of biodiversity stumps to biodiversity in Finland. We have relied on research data from Sweden so far. Several studies have investigated the importance of biodiversity stumps there.
"Swedish studies have also found that there are more species in biodiversity stumps than in regular logging stumps. In Sweden, endangered beetle species have also been found in high biodiversity stumps," says Junnikkala.
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