Stem discoloration of planted silver birch

The spread of discoloration in planted silver birch (Betula pendula Roth.) stems was investigated in 137 stands in Finland and the role of microbes was investigated in 71 stands. The colour changes noted in the pith of planted silver birches (18–65 years old) were very common but restricted and did not show unacceptable quality or reduction in veneer yield over 30 years. The horizontal spread of discoloration was generally less than 4 cm. The mean vertical spread of pith discoloration in planted silver birch trees was 3.2 m to 5.3 m in 30‐year‐old and younger stems, respectively. Dead and broken branches seem to be the main reason for harmful stem discoloration. The most common microbial community found in discoloured xylem includes primary invaders such as the non‐decaying fungi, Phialophora fastigiata, Phialemonium‐spp. and yeast‐like fungi and Enterobacter‐ and Pseudomonas‐type bacteria.