Dead Assets

With all the doom and gloom about dying ash trees in the news, maybe it's as well to bear in mind the wise words of Oliver Rackham - probably Britain's foremost authority on trees and woodlands - who observed that "a huge dead tree is still beautiful, and as good a habitat as a living tree". When a tree dies a whole host of organisms colonise and feed on it throughout its afterlife, which can last for decades. The National Trust owns two woodlands on the south bank of the River Swale at Richmond in North Yorkshire - Billy Bank wood and Hudswell wood - and has taken great care to ensure that there's a plentiful supply of dead wood lying around to act as a habitat for organisms that depend on this habitat.

This massive fallen beech is covered by a carpet of moss on its upper surface while ...

.. the underside hosts numerous fine young examples of Ganoderma fungus. This bracket fungus can live on the dead wood for a decade or more, producing a new layer of white sporing tissue on its underside every year.

I think this is probably a sycamore stump, hosting one of the densest populations of candlesnuff fungus Xylaria hypoxylon that I've ever seen.

There are also some decaying hazels that must once have been coppiced. Their decaying poles are the favourite substrate for hairy curtain crust fungus Stereum hirsutum. This is a young specimen ....

.... and here's a more mature example.

The Afterlife of Trees

I think it might have been Oliver Rackham, botanist and noted expert on woodlands, who once commented that the only object in woodlands more valuable than a live tree was a dead one, since they host so many species of wood-boring beetles and other insects that breed in dead wood. This ancient beech stump, in Durham University Botanic Garden’s new woodland nature trail, is riddled with emergence holes from insects that have bred in it, but its most conspicuous features are the magnificent specimens of the bracket fungus (Ganoderma sp.) that was almost certainly the cause of its death. This parasitic fungus weakens the tree and infected trunks typically snap somewhere above head height during gales. The fungus is perennial, so each year the bracket develops a new zone of spore-producing tissue around its periphery and generates so many spores that they cover the vegetation below with what looks like a layer of cocoa powder. You can estimate the age of the bracket by counting the number of ‘steps’ on its upper surface; each marks the end of a year’s growth. During their ten years of existence, these brackets must have produced billions of spores. You can read more about the woodland nature trail at http://www.dur.ac.uk/botanic.garden/?itemno=7173