The fruiting bodies of fungi are the visible evidence of the vast and intricate breakdown process which is happening all the time in our woodlands.
Fungi not only appear on living trees as parasites, they are also active on dead and decaying matter as saprophytes, most of them playing an important part in the breakdown of organic matter. Whereas green plants build up complex food substances from simple ones, using energy from the sun, fungi do the opposite. They have to take their sustenance from living and dead plants, since they lack the chlorophyll necessary to manufacture their own food. Therefore, they break down complex substances into simple ones on which they can feed and grow.
There are several hundred wood-inhabiting fungi in Britain and most of them are remarkably selective in the conditions they demand for survival. Some need wet or even soggy conditions while some prefer the relative dryness of standing trees. Generally, they need damp conditions in order to produce their fruit bodies and wet woodlands provide the ideal setting. Most are host specific, that is they infect only one species or group of species.
Infection of wood by fungi can take place in two ways. Standing trees are infected bythat land on them and. In damp conditions, start to grow. They send out threads known as hyphae. Which form a fine cobweb-like net – a mycelium – that penetrates the wood. Secondly, trees that have fallen down or are cut down are infected by the mycelium that is everywhere on the forest floor, living on the large amount of dead material – leaves, twigs and branches – which fall from the trees.
At certain times of the year the mycelium produces a fruit body-the mushroom or toadstool that we see. This fruit body distributesthat land and develop into a new mycelium, starting the process again.
Penetrating the wood
Once the tissues of the wood have been entered the mycelium often grows down the phloem and xylem, the sap and water conducting channels. Some fungi live off the food stored by the tree in its sap wood, while others actually absorb the substance of the wood, producing a condition known as heart rot.
An entire tree trunk can be full of mycelium, usually of one species, although some fungi extract all they can from the wood, leaving another to follow on and break it down further. One such example is the white, Pear-shaped, stump puffball (Lycoperdon pyriforme) which attacks wood that has been broken down by other fungi, such as the dark brown deer toadstool (Pluteus cervinus).
Fruiting times In general, the mushrooms and toadstools that grow in grassland fruit in late summer or autumn-earlier in the north and later in the south. Those that grow on wood tend to fruit later although there are exceptions. Autumn and early winter are good times to see interesting and attractive specimens in deciduous woodland.
Species to look out for include the aptly named beefsteak fungus (Fistulinci hepatica), which has a dark red, sticky upper surface and oozes a red juice when cut. It usually grows on oak, causing the wood to develop a deep, rich colour, which makes it very popular with cabinet makers. Oyster mushroom (Pleitrotus ostrecitus), has widely spaced gills on its underside and a grey-brown cap. It grows mainly on beeches, attached by the stalk that appears on its side. The razor strop fungus (Piptoporus betulinus) has a smooth, greyish skin which develops a corky texture with age. It is widespread on dead birch trees in the south of the British Isles, while its place is taken in the north of Scotland by the hoof-shaped tinder fungus (Fomes fomentarius), which causes white rot in the trees which it infects.
Hardly any deciduous wood lies on the ground for long without producing a crop of the banded bracket fungus (Coriolus versicolor), which has a velvety upper surface, banded with shades of yellow, brown and grey. Appearing at ground level, growing from the wood of the roots of beech tree stumps, is a remarkably large fan-shaped bracket fungus, Meripilus giganteus, which can measure up to 80cm (33in) across. It often grows in tiers, forming very large and conspicuous colonies.
Pholiota is a genus of yellow fungi with varying degrees of scaliness of the cap and stem, and is particularly common on dead beech trees, while charcoal pholiota (Pholiota carbonaria) grows in large numbers on burnt ground. These species are often confused with the beautiful golden Gymnopilus junonius, which is distinguished by the marked ring on its often swollen stem. It is generally found growing in dense clusters at ground level.
When the wood has been broken down into pulp or sawdust, some of the cup fungi, such as the wavy-edged Peziza repanda start to grow, the fruit bodies appearing in the autumn. If it is wet enough a remarkable species, Lycogala epidendrum may appear. It is a slime fungus, which is capable of spreading out into a thin layer until it is ready to fruit. The thin film then actually moves until it has gathered itself into pink balls about 1cm (2/5in) across which harden. Turn brown and break down to reveal a powdery mass of spores in the centre.
Elms killed by elm-bark disease are subsequently broken down by the autumn fruiting Lyophyllum ulmarium or by the velvet shank (Flammulina velutipes).