The Fungal World of the Beech Forest

Forest and Bird, Volume 21, Issue 2, 1 May 1990, Page 30

The Fungal World of the Beech Forest

by

and

Peter Buchanan

Peter Johnston

EXT TIME you walk through a beech forest, take a closer look around you. You will find a lot more there than just trees and birds. Among the plant world, you will also see the ferns, mosses, and liverworts; among the animal world, the insects. But there is yet another world separated from both the plants and the animals — the world of the fungi. In fact, so different are the fungi from all other organisms, they are considered to belong in a kingdom of their own. Mushrooms are one group of fungi, but there are many other different kinds. Fungi occur in vast numbers and live in all parts of the forest, from high in the beech tree to below the forest floor. An individual fungus grows as a cottonwool-like network of fine filaments called hyphae. The hyphae absorb the food essential for the fungus to grow. A single hypha is so narrow that it is usually invisible to the naked eye. But hyphae can be clearly seen when they mass together to form the reproductive or spore-producing structure, called a fruit-body. Common types of fruit-bodies include mushrooms, brackets, and puffballs. The fruit-body has the same function for a fungus (singular form of ‘fungi’) that a flower has for a green plant. Fruit-bodies enable fungi to produce spores, which are equivalent to the seeds produced in flowers of green plants. Just like seeds, the spores of a fungus can be distributed over wide areas and, when conditions are favourable, can germinate and grow into a new fungus. When the flower of a plant

is picked, the plant continues to grow. So too with a fungus; after the fruit-body has been picked, the hidden hyphae of the fungus keep on growing. Fruit-bodies of different fungi vary enormously in shape, and range in size from less than a pin-head to about half a metre across. Many fungi found in a beech forest are not found in other types of forest. Many of the species found in New Zealand beech forests are unique to this country. Different species of fungi have different roles in the forest ecosystem. Some are parasites feeding on a living beech tree, others (the saprophytes) are like scavengers and grow on fallen wood, dead leaves, or insect honeydew. Still others grow in the soil along with the living roots of trees, but without causing any harm to the tree. The world of the fungi, although rarely noticed, is one of amazing diversity.

Fungi Growing on Living Trees

Beech trees often look as if their trunks are covered with a lumpy, black carpet. This carpet is made up of millions of dark-coloured hyphae of many different types of fungi called ‘sooty moulds’. Sooty moulds appear to be feeding on the bark of the tree, but are in fact growing on honeydew produced by scale insects that are themselves sucking sap from the beech tree. The sweet honeydew is also food for nectar-feeding birds, lizards, wasps and other insects (see Forest & Bird November 1987). Sooty moulds are one group of fungi that do not produce their spores within

a visible fruit-body. Instead, their spores form amongst the carpet of hyphae, and are spread in the wind currents and by honeydew feeders. The ‘polypore’ fungus, Piptoporus, produces a large fruit-body. This fungus causes a wood-rotting disease of beech trees, and has a fruit-body similar in shape to a horse's hoof, but measuring up to half a metre across. The fruit-body has a texture like cork, with a water resistant skin on the upper side, and an underside covered with very tiny pores. About 15 pores would stretch across the head of a pin. The pores are the openings from the vertical tubes in which spores are produced. The spores form on cells lining these tubes and fall out to be carried away in the wind. Because this fungus produces its fruit-body high up in a beech tree, it is rarely seen in fresh condition. It may be better known to trampers and bush walkers in its fallen state; a sodden, amorphous, white mass on the forest floor, reminiscent perhaps of the carcass of some odd albino animal. Cancer-like swellings on trunks and branches of beech trees are caused by an unusual fungus called beech strawberry, beech orange, or more formally, Cyttaria. A tree infected by this parasite fungus shows a reaction similar to that of cancer in humans. Cells in affected parts of the tree grow and divide more rapidly than usual, and form hard, woody galls. In spring the fungus forms its pear-shaped or round strawberry-like fruitbodies on these galls. Spores develop in pits

on the surface of the fruit-body and after being released are dispersed by rain and wind. The often brightly coloured fruit-bodies are eaten by pigeons, possums, and insects. Different Cyttaria species are also found in beech forests of other parts of the southern hemisphere. In South America, some species are popular with the native Indians as food. Fungi on Fallen Wood and Leaves A quite different group of fungi live on fallen wood and leaves. These fungi are the decomposers. By decomposing dead plant parts, not only do the fungi grow and reproduce, but living plants can use the nutrients which are returned to the soil. Decomposer fungi are called saprophytes, as opposed to the parasites (or pathogens) that attack a living tree. Many species of polypore fungi, with fruitbodies similar to those of Piptoporus, are saprophytes on fallen wood. They produce enzymes that break down parts of the plant cell wall, and in so doing cause the wood to rot. Depending on which parts of the cell wall

are destroyed, the polypore fungi are divided into two groups, brown rot and white rot fungi. Brown rot species cause a rot in which the decayed wood becomes brown, cracked, and eventually collapses into a fine powder. White rot fungi are more common than brown rot fungi and cause the wood to become white to pale brown, often wet, and stringy. Ganoderma is one of the most common white rot fungi in beech forests, and in other forest types. Its fruit-bodies are like shelves or brackets sticking out from the wood. Their

appearance, especially when on a dead standing trunk, has led to a number of amusing popular names — in Stewart Island, for example, they are known as ‘moa droppings’ (although you have to believe that the droppings are carried aloft as the tree grows!), and in Japan as ‘monkey seats’. The upper side of Ganoderma fruit-bodies is usually covered with a brown powder, a deposit of thousands, if not millions, of spores. The lower, pore surface, from which the spores are produced, is either white or dark brown, depending on the stage of

growth. When the pore surface is white, it can be scratched easily to show the brown tissue beneath. Artists (graffiti and otherwise) can exploit this, and hence Ganoderma is also known as the ‘artist's conk’. Each year, the long-lived, woody-hard fruit-bodies develop a growth ring, similar to the annual rings of trees, and in time the fungus can grow to a large size. Many species of mushrooms are also saprophytes. Mushrooms are familiar to most people as a delicious vegetable bought at the supermarket, or as the object of expeditions

across farmland on crisp autumn mornings. But the word ‘mushroom’ in a botanical sense refers to all fungi that have fruit-bodies with gills on the underside of a cap, including all those species popularly called ‘toadstools’. A mushrooms spores are produced on the gills, and are spread by the wind. Many types of mushrooms are edible, but there is no simple rule to distinguish edible from poisonous types. Accurate identification of any mushroom is the first and most important step before thinking about eating it. For many species of mushroom in New Zealand, however,

there is no information about whether they are edible or not. One common mushroom on wood in beech and broadleaf forest throughout New Zealand is Armillaria. It grows in tight clumps with several mushrooms arising from a single point. To the Maori it is known as ‘harore’ and is one of a small number of fungi eaten by the tangata whenua. The most common species of Armillaria has a slimy cap, and when cooked makes a tasty soup. Even if mushroom fruit-bodies of Armillaria are not found, its effect in the forest can often be seen in the unusual patterns left in rotted wood. Wood in a late stage of decay by Armillaria is black with many oval pockets, a so-called large pocket rot. Surprisingly, the same fungus outside of the beech forest environment becomes a damaging parasite of pine trees, and even of kiwifruit vines. In some parts of New Zealand, conversion of native forest to pine plantations has proved to be uneconomic due to the death of pine

seedlings caused by Armillaria spreading from dead stumps and roots of the cleared forest. ‘Fungus icicles’ is the apt nickname for an intriguing looking, rare fungus called Hericium. The fruit-body, which forms on wood, is made up of fleshy lobes or branches with coral-like cascades of circular, pointed teeth. The spores are formed on the surface of these teeth. The fungus was known to the Maori as ‘pekepekekiore’ and was occasionally eaten. On the floor of a beech forest, there is usually a thick layer of fallen, often brightly coloured leaves. If the upper layers of leaves are swept aside to reveal the older, partly decomposed leaves, fine stands of fungal hyphae may be seen binding the leaves together. Some of these hyphae will belong to mushrooms growing in the litter. Others may be from fungi with smaller, semi-microscopic fruit-bodies. With careful examination of the upper layers of leaves some of these fruitbodies may be seen. One such fungus is the

cup fungus, Lanzia, in which the spores form in a cup and are forcibly shot out like bullets into the wind currents. Another is Hypoderma which produces spores within enclosed sac-like fruit-bodies partly embedded in the leaf tissue. The slit-like opening of this fungus is marked by a line of bright red cells, and in wet weather the sides of the opening fold apart, like an opening mouth, to allow the release of the spores. Fungi Growing Within the Soil Walk through a beech forest in autumn and you can't fail to be impressed by the colourful array of mushrooms fruiting on the forest floor. Most of these will be fungi that are only able to grow in a close relationship with the roots of beech trees. Such a mutually beneficial (‘symbiotic’) relationship between plant roots and fungi is very common and is called a ‘mycorrhiza’. Hyphae from the fungal partner of the mycorrhiza form a mantle surrounding the root, much like a sock covers

a foot, and although the hyphae penetrate between the outer cells of the root, the root is not damaged. In this association between tree and fungus both partners derive benefits; the fungus takes organic compounds such as carbohydrates from the tree, while the tree uses the fungus as an extension of its own root system, to absorb minerals from a larger mass of soil. Mycorrhizas form only between certain tree/fungus combinations, and beech trees, along with tea tree, are the most prolific mycorrhizal forming trees in New Zealand. Many species of mushrooms are involved as mycorrhizas including species of Amanita, Russula, Cortinarius, and Paxillus. These mushrooms are often brightly coloured, such as the green Russula, violet and red Cortinarius species, and the orange-brown Paxillus. Another closely related group of mycor-rhiza-forming fungi are the boletes. With their stalked, mushroom-shaped fruit-bodies and pores instead of gills on the underside of the cap, they look like they might be a cross between a mushroom and a polypore. Among the boletes are some good edible species, including in France the famous ‘CEG, Yet another group, the hydnoid fungi, has mushroom-like fruit-bodies but the underside

is covered not with gills or pores but with pointed teeth. And then there is the elegant violet pouch fungus, Thaxterogaster, that looks a bit like a puffball, but is in fact a mushroom that has lost its way, forgetting how to open up its gills. Other fungi related to Thaxterogaster grow only below the ground, but such ‘hypogeous’ species are unlikely to be encountered except by kiwis and the most persistent fungal enthusiasts. In parts of Europe, it is the hypogeous ‘truffle’ that is so sought after, but so hard to find unless you own a pig trained to sniff out the delicacy. If the fruit-body is below the ground, how are the spores released to allow the fungus to spread? It would seem that in New Zealand where native fungus-eating mammals are absent, slugs, insects, and birds such as the kiwi and weka may eat and hence spread the fungus. The tremendous variety of shape, colour, texture, and structure of fungi mentioned by no means exhausts the range. Within the beech forest live hundreds of other types of fungi, such as those growing on dead insects, on dung, and even in water. The fungi are a integral component of the beech forest. In number and diversity they far exceed the meagre range of green plants, and without them the forest could not survive.

Nothofagus (beech) forests are restricted to certain parts of the southern hemisphere, and their origins can be traced back to similar forests of 100-150 million years ago that grew on the giant land mass of Gondwanaland. The present distribution of both Nothofagus and of beech fungi provide evidence for the breakup of Gondwanaland and for continental drift. Many species of fungi in New Zealand beech forests have close relatives on beech in Tasmania and in South America. For further information on fungi of New Zealand, consult the excellent illustrated guide: Mushrooms and Toadstools, by Marie Taylor (1981), Mobil New Zealand Nature Series, A.H. & A.W. Reed. Peter Buchanan and Peter Johnston are mycologists employed by DSIR Plant Protection, Auckland to study identification and classification of New Zealand fungi. They

work in the fungal herbarium, PDD, which contains over 50,000 dried specimens of fungi, in particular from New Zealand and nations of the South Pacific. The authors thank Mary Bedford for making available the transparencies of the late Jack Bedford. #