STEM DISCOLORATION OF PLANTED SILVER BIRCH

The spread of discoloration in planted silver birch (Betula pendula Ro th.) stems was investigated in 137 stands in Finland and the role of m icrobes 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 vene er yield over 30 years. The horizontal spread of discoloration was gen erally 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 yo unger stems, respectively. Dead and broken branches seem to be the mai n reason for harmful stem discoloration. The most common microbial com munity found in discoloured xylem includes primary invaders such as th e non-decaying fungi, Phialophora fastigiata, Phialemonium-spp. and ye ast-like fungi and Enterobacter- and Pseudomonas-type bacteria.