The urea treatment of silver birch (Betula pendula Roth) logs promotes wood decay and wood discoloration

Silver birch Betula pendula Roth is a widely distributed tree species in northern Europe, the wood of which is extensively used to produce plywood and veneer. However, birch wood is highly susceptible to fungal decay and discoloration. This study investigated the effectiveness of urea treatment against fungi causing discoloration in birch logs. The effect of urea treatment was evaluated in two settings, i.e. in the forest and in the log yard. In the forest, 80 one-meter-long stem segments were produced and half of them were treated with 35% urea solution and the other half with water. To simulate mechanical bark injury, half of the segments were deliberately damaged before storage. In the log yard, 60 stem segments were similarly prepared to assess fungal species colonizing wood during long-term storage. The results showed that urea-treated and bark-damaged logs exhibit the highest rate of wood discoloration, which increased with prolonged storage. Fungal isolation from wood samples identified a higher diversity of fungal species in samples from the log yard. The most frequently isolated fungi were ascomycetes from the genus Ophiostoma. In conclusion, the results demonstrated that the urea treatment is an ineffective measure against fungi causing discoloration in birch wood.