There are two fungi that cause butt rot: Fomitopsis annosa and Bjerkandera borealis. The losses they cause in pine forests are relatively mild, the share of rotten trees is between 6 and 12 % and the rot is restricted to the butt end of the tree.
In forests dominated with spruce the losses to timber are more notable. The share of trees infected with butt rot is between 10 and 40 % and of the volume at least 12 per cent. The more barren the heath forest site the greater the defect caused by decay. In the forests on peatland the pine swamps and spruce moors are the most affected.
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