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Birds benefit from evergreen trees in fir forests –

During the 1990s, new requirements were introduced to be considered generic when forests were felled, meaning that evergreen trees and groups of deciduous trees were left behind. It is also part of the testimony of the forest that came around the same time. The question is how this works in the long term, when the new forest grows on the cuttings and surrounds the preserved deciduous trees.

To see how bird life was affected by this consideration, a research group led by SLU compared 32 groups planted with fir trees in the early 1990s. Half of it was crystal clear from the start and half of it was preserved from older deciduous trees. By analyzing old photographs (aerial photographs), the researchers succeeded in finding suitable areas in Skåne, Småland, Halland and Västergötland.

It wasn’t quite easy, but in the end we had all the pieces in place and were able to get out into the field and assess the bird life, says Professor Mats Lindblad, who conducted the study with researchers Adam Felton and Johann Elmberg.

Immortality trees looking at trees

Trees which are left when one is out of consideration for nature are called evergreen trees or considered trees. The idea is that they should stay until they die and disintegrate in a natural way.

Beech, birch and oak were common

To reduce the risk of study areas being affected by the surrounding forest landscape, platforms of at least three and up to ten hectares in size were selected. And in order not to confuse abandoned eternal trees with naturally renewed birch, the remaining trees were selected with a diameter of at least 20 cm in chest height. The number of trees remaining was an average of 10 per hectare, with fairly large differences between the 16 pavilions. The most common evergreen trees were beech, birch, and oak.

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The results clearly show that there are more species and more individuals in the stands with the preserved deciduous trees. The most obvious difference was the difference between burrow and leaf specialists, including the crow, the nutcracker and the entita. The ringed pigeon, which is not an uncommon species, was also three times more common in deciduous stands, compared to pure spruce forest.

Deciduous trees are important to birds

Typical fir-forest birds were equally common in all groups and were therefore not deterred by deciduous trees. Among them are the kingfisher and the black dream.

Our conclusion is that general consideration works well in this case. Although deciduous trees make up a fairly small portion of the population, they contribute to the diversity of birds, says Mats Lindblade.

Other studies show that individual perennial oaks also benefit insect diversity. In other words, diversity benefits from several aspects.

– These are the terraces where today the individual deciduous trees are surrounded by a rather dense and lush forest of fir, even if once thinned. Now the fir forest continues to withdraw. It is important to cut down and trace deciduous trees so that they do not suffocate in the surrounding spruce forest. Mats Lindblade concludes that when it comes to the final cut, there is every reason to identify deciduous trees and preserve them for at least another generation with spruce.

Scientific material:

Broadleaf retention benefits of bird diversity in mid-rotating conifer production platforms. Forest environment and management .

Contact:

Mats Lindbladh, Professor Emeritus, Department of Southern Swedish Forest Sciences, Swedish University of Agricultural Sciences, Nareb, [email protected]

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