NEW AVENUES FOR UNDERSTANDING PROCESSES OF TREE DECAY

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Abstract
The interrelationships between trees, and the fungi that inhabit and decay their xylem, are dynamic, complex and difficult to analyse into simple sequences of cause and effect. This is because both participants function, and interact, as highly versatile, open-ended or “indeterminate” hydrodynamic (“self-plumbing”) systems. As such they are capable of varying their pattern of development to accord with environmental circumstances by means of local feedback processes that lead to the opening up or sealing off of internal and external boundaries. Boundary-sealing, or “insulating” processes involve metabolic pathways that in leading to the production of water-resistant compounds and cell death would be detrimental within organisms with determinate development (e.g. many animals). However, they enable trees and fungi to switch functional modes, to conserve and redistribute resources, and to protect and repair their communication channels. The primary circumstance in trees that creates the opportunities and defines the avenues for exploitation by decay fungi is the dysfunction of xylem as a water-carrying tissue. Such dysfunction can be due to a variety of both intrinsic and extrinsic factors and, providing that it is sealed off from life-supporting tissues, need not in itself be detrimental to the tree; it may even be beneficial. It is therefore inapt to regard decay, or its containment, purely as the outcome of conflict between the “aggressive” forces of fungi and the “defensive” responses of trees. Better understanding may be achieved by identifying the varied processes by which dysfunction is induced and how they relate to the spectrum of types of behaviour, or “colonization strategies” that enable decay-causing fungi to become established. Such understanding may help in the development of a more systemic practical approach to tree decay.