An introduction to poroide fungi
7. Forest regions of Europe
The distribution of polypores and other wood inhabiting fungi is dependent on many factors such as climate, type of vegetation and host range. These factors are of course interlinked, but it is often that a single factor is the main limitation to the distribution of a species.
After the description of each species we have included a section on its distribution and used the terms: "boreal", ”Mediterranean", "boreal conifer forests" etc. See fig. 12.
Northern Coniferous forest
This type of forest invaded Europe from the south (Pinus sylvestris) and partly the east (Picea abies) after the last glaciation and the latter is still moving westward, at least on the Scandinavian Peninsula. This forest region stretches further to the east and also covers the Northern parts of North America and it is often in its drier and cooler aspects called "taiga". The region has a common set of hosts and a similar complex of polypores. Almost all polypores listed from this region are circumglobal in the boreal regions.
In the boreal part, the region is dominated by Picea and Pinus, the former occuring on better soils, the latter on poorer and drier soils. In the central European mountains Abies and Larix are also common.
Deciduous woodland is dominated by species of Betula in northern areas where they constitute a very conspicuous zone along the timberline, the so called subalpine birch forest. Other hosts include Salix spp. especially Salix caprea and Sorbus aucuparia, Populus tremula, Prunus padus and Alnus incana.
Central European hardwoods
This region stretches across Europe between the northern boreal coniferous forest and the Mediterranean evergreen forest. The zone may also be called the Fagus-zone after its most prominent hardwood tree.
When man settled in Europe after the last glaciation he soon started to clear this type of forest and only in some national parks there are remnants and small pockets left of this once coherent forest.
The most prominent coniferous trees are Pinus, Taxus and Juniperus. The dominating hardwood trees are Acer, Aesculus, Alnus glutinosa, A. nigricans, Carpinus, Corylus, Cotoneaster, Crataegus, Fagus, Fraxinus, Ilex, Laurus, Platanus, Populus, Quercus, Tilia, and Ulmus.
The Mediterranean evergreen forest
This forest is even more degraded than the Central European hardwood forests. Some 2000 years ago overcutting and overgrazing started, and slowly the soil and the forests disappeared. Today only remnants remain, usually with some degree of degradation. Small pockets, national reserves and parks have been established in the best areas in an effort to restore some of the splendour of this forest type.
This region is characterized by a number of species of conifers with evergreen needles and evergreen hardwoods, especially Quercus spp. The climate is harsh with most of the precipitation falling in winter and early spring. The summer is very dry and hot. In many areas there are thickets of thorny bushes making up a special type of vegetation called macchia in Italian and maquis in France and Spain. The mycota of the wood inhabiting species in this vegetation is characterized by few species, partly because of the climate and partly because of the lack of suitable substrata.
In addition to the trees and plants mentioned above, there are numerous exotic trees planted all over Europe and many of them are today also naturalized. Typical examples are Acacia spp., Robinia pseudoacacia, Eucalyptus spp. and some American and Japanese gymnosperms.
Most polypores are strictly saprotrophic and utilize dead wood as a food source. A few species of Albatrellus, Boletopsis and Coltricia, are terrestrial and utilize soil organic material or are mycorrhizal (Danielson 1984). The saprotrophic polypores are extremely important in their role as decomposers in recycling of carbon in the world ecosystem.
Polypores that grow and produce basidiocarps on living hosts are of two kinds. Some are restricted to the non‑living heartwood in living hosts and do not invade and kill the outer living tissues and are commonly referred to as heart rot fungi.
A relatively small number of polypores, often called biotrophs, are true pathogens and are capable of invading and killing living sapwood and causing death of living hosts. Polypores that are particularly important pathogens in Europe as heart rot fungi include Heterobasidion annosum, Fomitopsis pinicola and Phellinus pini (the major causes of volume losses in conifers), Phellinus igniarius in hardwoods, and numerous other species in various genera.
Virtually every important timber species in Europe is invaded and decayed by at least one polypore species and most are hosts to several. They are also important causes of decay of timber in houses and other structures, utility poles, pilings, guard rails, mine timbers etc. Most of these are brown rot fungi.
Gloeophyllum sepiarium and a number of Antrodia spp. are probably the most important polypores that cause decay in houses. Gloeophyllum sepiarium is especially common on wooden roofs due to its high temperature tolerance while the Antrodia spp. occur in basements and similar places where the temperature rarely exceeds 30° C.
Brown rot fungi are also major causes of decay of conifer wood mine timbers and utility poles in Europe. Antrodia serialis, Antrodia xantha and Oligoporus spp. are important in this respect. White rot fungi also decay wood in service but are mainly found on hardwoods. Trametes versicolor and T. hirsuta are examples of white rot fungi in this category.
Fig 12. Forest regions of Europe. 1: Northern coniferous forest, 2: Central European hardwoods, 3: Mediterranean evergreen forest (modified after Polunin & Walters 1985).
Fig. 13. Distribution of (1) Picea abies and (2) Pinus in Europe.
Fig. 14. Distribution of (1) Fagus sylvatica and (2) Abies alba in Europe.
Fig. 15. Distribution of Quercus in Europe.