Internal decay assessment using drilling resistance in mature common alder (Alnus Glutinosa (L.) Gaertn.) Stands

Abstract

The occurrence of wood decay in common alder stems (Alnus glutinosa (L.) Gaertn.) was studied based on data obtained in seven matured stands in Latvia age ranging from 65 to 122 years. The study was intended as a pilot study to test the possible use of nondestructive micro-drill (Rinntech Resistograph® R650) for detection of the different stages of wood decay within common alder stems. The drilling profiles were visually compared with the wood samples obtained from increment borer or cross-cut sections at actual drilling height. The study confirmed initially proposed hypothesis that drilling profiles obtained using the Resistograph enabled the diagnosis of the common alder stem health condition. Wood decay stages – spongy rot and cavity can be detected successfully by the Resistograph; however, this non-destructive method does not detect discoloration in the wood, which is the earlier stage of wood decay. We found significant (p<0.05) positive correlation between decay occurrence and some of examined forest stand characteristics such as mean stand diameter, stand age and mean tree volume. The tree inspection showed that the preservation of old common alder stands can lead to a significant loss of wood quality. Based on this pilot study, we conclude that if the economic interests are prioritized in management of studied stands, the reduction of actual harvesting age of the common alder stands have to be considered.