AN OVERVIEW OF WOOD DEGRADATION PATTERNS AND THEIR IMPLICATIONS FOR TREE HAZARD ASSESSMENT

Summary

The identification of decay fungi in tree hazard assessments is of little value unless information about the likely mechanical effects of the decay can thereby be gained. To this end, knowledge of the broad category of decay caused by the fungus concerned brown-rot, white-rotor soft-rot, is useful but generally insufficient, since the mechanical effects within each category may vary greatly. High resolution light microscopy, combined with strength tests, can provide useful details of the wood degradation patterns that occur in a given host/fungus combinations. Studies of several such combinations have shown the biomechanical importance of the preferential degradation of particular zones within the woody structure in the earlier stages of decay. In this context, the ability of certain white-rot fungi such as Inonotus hispidus to switch between different modes of degradation, including soft-rot in some cases, is of considerable significance. These new data help to explain previous, anecdotal observations; for example the different effects of decay by I. hispidus on its host species, and the brittle decay caused by Ustulina deusta. Such information can provide objectivity in tree hazard assessments, allowing the residual strength of partially decayed wood to be taken into account.