External timber quality of birch in birch-spruce mixtures
The Swedish forest management model, largely based on monocultures of conifer species, has increasingly come under scrutiny. Its disadvantages to biodiversity, recreation and climate change susceptibility incentivize alternative ways of forest production. Mixtures with a secondary species is one...
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| Format: | Second cycle, A2E |
| Language: | Swedish Inglés |
| Published: |
2018
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| Online Access: | https://stud.epsilon.slu.se/13950/ |
| Summary: | The Swedish forest management model, largely based on monocultures of conifer species, has
increasingly come under scrutiny. Its disadvantages to biodiversity, recreation and climate
change susceptibility incentivize alternative ways of forest production. Mixtures with a
secondary species is one such alternative. Birch and spruce, two species native to Sweden, are
well-known to function together. Mixtures of the two exist today already, although the species
are usually treated with different goals in mind. Further encouragement of forest owners is
necessary for the practice to become more widespread.
This thesis attempts to reflect upon whether naturally regenerated birch in birch-spruce
mixtures have a high enough timber quality to make the birch valuable from an economic
perspective. The aim of the study was therefore to assess external timber quality of naturally
regenerated birch in birch-spruce mixtures in southern Sweden. The hypotheses to be
addressed was a) that naturally regenerated birch trees in Norway spruce plantations fulfill the
requirements for high quality saw timber and b) that the quality of the future crop trees of
birch is lower when the surrounding competition is of Norway spruce instead of other birches.
Birch quality was assessed externally in 27 birch-spruce mixture stands in Götaland.
Straightness, leaning, stem damage, spike knots and forks were among the studied variables.
The result showed that naturally regenerated birch trees in Norway spruce plantations
generally did not fulfill the requirements for high quality saw timber, but had a potential for
intermediate quality saw timber.
Furthermore, the quality of the future crop trees of birch was lower when the surrounding
competition was Norway spruce instead of other birches.
The actual cause for the differences is not possible to state with this type of forest survey,
where the earlier management is uncertain and the objectives of the different forest owners
are unknown. Further research is needed to clarify this, and to determine how to achieve an
optimization of birch-spruce mixtures, with yields of both high quality birch timber and
spruce timber. |
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