DEVELOPMENT OF DECAY IN THE SAPWOOD OF TREES WOUNDED BY THE USE OF DECAY DETECTING DEVICES

Abstract

Summary The effects of drilling holes with the IML-Resistograph and an increment borer were examined in London plane Platanus x hispanica Muench. and ash Fraxinus excelsior L. trees naturally infected with Inonotus hispidus. Eight months after inflicting the wounds on the lower stem, trees were felled and dissected. Microorganisms were isolated in pure culture and identified from the decayed wood, host-fungus interface, discoloured wood and the sapwood. In both hosts the extent of discoloration and decay within the sapwood and also the frequency of isolation of I. hispidus from these altered zones were greater after wounding with the IML-Resistograph than with the increment borer. These differences may be related to micro-environmental conditions. Tightly packed wood shavings are retained within the IML-Resistograph drill holes, whereas the holes created with the increment borer remain open, allowing ingress of air into the sapwood. Such alterations in growth conditions seem to be unfavourable for growth of Inonotus hispidus, which reacted by forming mycelial plugs that firmly sealed each of the increment borer holes. As mycelial plugs were never observed in wounds induced with the IML-Resistograph, it appears possible that pre-existing conditions are not greatly modified and that the fungus can therefore grow out into the adjacent sapwood more readily. Additional laboratory studies on a naturally infected beech (Fagus sylvatica L.) and ash showed that cross-infection via drills contaminated with fungal propagules appears unlikely.