Heart-rot and associated fungi in Alnus glutinosa stands in Latvia

The interest in Alnus glutinosa (L.) Gaertn. as plantation species has increased during last years, but its prospects should be evaluated from the perspective of forest health. The aims of the present study were to: (1) estimate the incidence of stem decay in Latvian A. glutinosa stands, (2) measure the extent of decay within individual stems and on a stand level and (3) identify decay-causing fungi. In four A. glutinosa stands, 450 trees were randomly sampled with an increment borer and the presence/absence of decay was recorded. As a result, 112 sound-looking and 338 decayed trees were detected, and a corresponding number of wood samples were collected for fungal isolations. A total of 34 stems with decay symptoms were cut to measure the extent of internal decay. The incidence of decayed stems in studied stands was 75.1% on average. The length of the decay column was 7.7 +/- 5.4 m on average, and that of spongy rot was 4.2 +/- 4.5 m on average, implying that yield losses for fully stocked 80-years-old A. glutinosa stand would comprise 49.2% of the total stand volume, and the losses from spongy rot alone -30.5%. In total, 1134 isolates representing 68 fungal taxa were obtained. The most common decay-causing fungi were Inonotus radiatus and Armillaria sp.