Rusokääpä Mölylässä. Kuva: Keijo Savola

Pycnoporellus fulgens in Möylä. Photo: Keijo Savola

Decomposers of trees

Polypores, corticioid fungi and some tooth fungi are wood-decaying fungi that derive the nutrients that they need to grow by decomposing trees. Once the fungi have used up all the suitable nutrients, they eventually vanish from the tree trunk. By then, with any luck, they have already spread their spores to other suitable decaying tree trunks in the forest area.

Approximately 250 species of polypores and 400 species of corticioid fungi have been found in Finland. The number of decomposer tooth fungi species recorded is over 70.

Creators of biodiversity

As decomposers of trees, polypores, corticioid fungi and tooth fungi play a very important role in the ecosystem. They are the only organisms capable of decomposing wood and releasing the nutrients contained within in a form that other organisms can re-utilise.

The wood decomposed by polypores, corticioid fungi and tooth fungi also serves as a habitat for a wide range of different insects. These insects are, in turn, consumed by other animals, such as birds. Some birds, such as woodpeckers and willow tits, also excavate nesting holes in soft and decaying wood, which are also used by other bird species, such as various tits.

It has been estimated that as many as a third of the trees contained in a naturally developed forest are in different stages of decomposition or dead. Many wood-decaying fungi specialise in decomposing specific tree species or only feeding on trees that are in a specific stage of decomposition, so that once one species of fungus has decomposed the tree up to a certain point, it is replaced by another species of fungus. As such, leaving decaying wood in forests greatly increases natural biodiversity.

In efficiently managed commercial forests, trees are felled before they can start to decay. As a result, many wood-decaying fungi, as well as many of the species that follow in their wake, have become rare or endangered.

How to distinguish between polypores, corticioid fungi and tooth fungi?

Wood-decaying fungi are composed of two parts, the mycelium and the fruiting body. The web-like mycelium lives inside the wood and cannot be seen by the naked eye. Wood-decaying fungi usually live for several years as mycelium before producing a visible fruiting body on the surface of the wood.

Polypores usually form clearly protruding fruiting bodies. The fruiting bodies can grow quite large, and remain attached to the side of the tree trunk for several years. The underside of the fruiting body is composed of tubes, like the underside of a bolete mushroom cap. The fruiting bodies of corticioid fungi, on the other hand, are smooth and grow parallel to the tree trunk. The fruiting bodies of tooth fungi, meanwhile, have undersides composed of teeth, as the name implies.

The areas surrounding Vanhankaupunginlahti include old forests that surveys have designated as especially valuable category I polypore areas in Helsinki.

The old forest of Kivinokka

Nuori kantokääpä. Vanhemmiten punainen alue muuttuu tummanharmaaksi ja reuna puolestaan valkoisesta punaiseksi. Kuva: Taina Tervo

A young red-belted polypore. As the fruiting body matures, the red area turns dark brown while the edge turns from white to red. Photo: Taina Tervo

A young red-belted polypore. As the fruiting body matures, the red area turns dark brown while the edge turns from white to red. Photo: Taina Tervo

The old forest in the north part of Kivinokka has long been allowed to develop in a semi-natural state, as a result of which there is plenty of decaying wood in the area. Despite its small size at 13 hectares, an impressive 75 polypore species and 108 corticioid and tooth fungi species have been found in the area. These are some of the highest numbers of species recorded in areas of this size in Finland. The old spruce forest of Kivinokka is an especially important habitat for polypore and corticioid species that inhabit spruce trees, but the area is also home to many species that grow on pines and broad-leaved trees.

One of Kivinokka’s greatest rarities is the extremely endangered Physisporinus crocatus, which grows on large felled spruces and is only found in approximately a dozen places in Finland. Kivinokka has also been found to contain several regionally endangered and near-threatened species, as well as a whopping 43 indicator species, which reflect the conditions of natural forests that also have old trees in them. The number of indicator species found in Kivinokka is notably high.

Kivinokka seems to be experiencing an influx of demanding fungi that inhabit spruce trees, as over half of the area’s threatened or near-threatened species of fungi that grow on spruces were first recorded in autumn 2011 or later.

The forest of Mölylä

The forest of Mölylä has only been surveyed for polypores on one single day for a total of seven hours. That single survey resulted in the identification of a total of 64 different species of polypores, as well as five other indicator aphyllophorales. Considering the short survey period and the small size of the area (13 hectares), the number of species found is notably high. The forest of Möylä is an important habitat particularly for polypores inhabiting spruce trees, but the area is also home to many species that prefer decaying broad-leaved trees.

Möylä’s specialty is Antrodia cretacea, which inhabit large spruce trees decomposed by red-belted polypores. Besides Mölylä, the species is known to grow in only two other locations in Finland. Mölylä has also been found to house four regionally endangered and one near-threatened polypore species.

The herb-rich common alder forest of Pornaistenniemi

Pornaistenniemi is a seaside herb-rich forest, one of very few such forests that have been preserved in their natural state. Although Pornaistenniemi only covers an area less than eight hectares, it has been found to house 56 polypore and 99 corticioid and tooth fungi species. Of these, 30 are indicator species for valuable deciduous forests. The wide range of species is a result of the fact that the area has long remained a nearly unmanaged natural forest. Only dangerous trees have been felled in the area and left to decompose in place. As such, the area provides an excellent habitat for wood-decay fungi specialising in broad-leaved trees.

Pornaistenniemi has also been found to house several threatened and near-threatened polypore, corticioid fungi and tooth fungi species.