Fungi attacks: decay in trees is most likely a group effort

Adapted from ‘Trees & Fungi: Their Complex Relationship’ by Professor Lynne Boddy – Part 6 

There are broadly three types of decay, these being soft rot (which leaves the wood soft and spongy), brown rot, where the wood is left brittle and brown from decay enzymes, and white rot, where the decay enzymes bleach the timber.

Rarely will a single species of fungus be responsible for the decay of an individual tree, even if in theory that could be the case.

More often than not, several strains of the same species are present and these ‘communities’ change in relevance over time.

With soft rot, the wood is left soft and spongy. With white rot, sometimes with the lignin (glue) degrading before the cellulose, the tree loses its strength.

Identifying the extent and location of decay in trees is important for management and safety. 

We can use a range of tools. These include an incremental borer, which removes a core of wood which can then be analysed for decay. 

An endoscope (small camera on a cable) can be used to explore cavities to assess their extent and whether remaining wood is sound. A resistance drill measures the pressure needed to drill into the wood. Where there is greater resistance, the wood is more sound and stronger. In the previous issue of The World of Trees, the use of sonic tomography was detailed. This measures the speed of sound waves travelling from wave sensors. Sound travels faster through a solid material, and slower through spaces. This provides a picture of where sound and strong timber is. We can also use a plastic hammer as a basic instrument to detect more obvious decay.

Some fungi arrive at new food sources, namely ‘wood’, through the soil beneath them, but most fungi spread via spores. These need to land and germinate in suitable conditions during the brief period in which they are viable. Extremes of temperature are not conducive to germination, growth and ultimately survival.

Insufficient or excess moisture levels can also be problematic. However, if conditions are suitable, the spores can germinate and their mycelia can become established.

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