Geographic Distribution Zones

The boreal zone is climatically represented by short summers and long winters. It is also climatically divided into oceanic parts with higher precipitation and continental areas with lower precipitation, for example western parts of Fennoscandia have an oceanic climate, while towards the east the climate becomes more continental (e.g. Ahti et al., 1968; Tuhkanen, 1980). The boreal zone has also been divided latitudinally, that is hemiboreal, southern boreal, middle boreal and northern boreal vegetation zones (Ahti et al., 1968). The hemiboreal zone is characterized by temperate broad-leaved tree species such as oak (Quercus robur in Europe or Q. mongolica in the Far East) and ash (Fraxinus excelsior in Europe or F. mandschurica in the Far East) mainly on better soils, and spruce (Picea) or pine on poorer soils (Esseen et al., 1997; Dai and Penttila, 2006). All the other zones are characterized by the dominance of coniferous tree species, together with deciduous tree species typically belonging to the genera Betula, Populus or Salix. Due to the dominance of coniferous tree species the boreal zone is also often called the northern coniferous forest region (e.g. Gilbertson, 1980). In the boreal zone, the host tree species have wide distributions, and although they are not circumpolar, the species in different continents are closely related both taxonomically and ecologically (e.g. Hallenberg, 1991). This, in addition to the rather continuous forest belt across the boreal zone and the ability of fungi to spread long distances via spores, contributes to the fact that a very large proportion of boreal wood-decay basidiomycetes seem to be widely distributed or circumpolar (e.g. Gilbertson, 1980; Hallenberg, 1991, 1998; Chapter 13).

Gilbertson (1980) analysed the distribution of wood-decay polypores and corticoid basidiomycetes shared between North America and other continents and found that the highest number was from the boreal zone (80-90% shared species) and that the fraction of shared species decreases in warmer regions. For example, less than 60% of the polypores found in temperate forests of East Asia are also present in North America (Nunez and Stokland, 2000) while only 30% of the polypores species found in New Zealand are shared with North

America (Gilbertson, 1980). We conducted an analysis of the distribution of po-lypores in the northern hemisphere using two datasets collected from different zones of boreal East Asia (Table 2). The number of shared polypore species between different continents and the number of circumpolar species were approximately 10% higher in the more northern Kamchatka and Magadan areas in Russian Far East than in the hemiboreal zone in north-eastern China (Table 2). The lower number of shared and circumpolar species in the hemiboreal zone in north-eastern China can largely be explained by the high number of endemic species (21 species; Dai and Penttila, 2006) in comparison with the Kamchatka and Magadan areas (5 endemic species; data collected by Parmasto, Kotiranta and Mukhin, personal communication). A similar trend is also present for vascular plants, especially trees (Adams and Woodward, 1989; Latham and Ricklefs, 1993; Qian and Ricklefs, 2000). The lack of Pleistocene glaciations compared to other parts of Eurasia or North America, including Kamchatka and Magadan (Zhang et al., 2006), favourable geography (continuous dispersal routes between East Siberia and South-East Asia for millions of years allowing coexistence of boreal, temperate and tropical species) and high numbers of host tree species are the likely explanations for the higher species diversity of polypores in north-east Asia (Dai, 1996; Nunez and Stokland, 2000; Dai and Penttila, 2006).

A comparison of the climatic specialization of wood-inhabiting fungi is presented in Table 3. Although records are far from complete, very few polypore species are predominantly boreal and have a restricted distribution. In the temperate zone the number of endemic polypore species is definitely higher in East Asia than in Europe or North America, probably because of limited spread of glaciers in East Asia during the Ice Ages (Dai, 1996; Nunez and Stokland, 2000). Species richness of polypores and the number of endemic polypore species are higher in the hemiboreal zone of East Asia than, for example in the boreal Fennoscandia (Dai and Penttila, 2006). However, we need more information on the species distribution from boreal East Asia and North America to verify whether the boreal zone in East Asia is more species rich and has more endemic species than Europe or North America.

In Europe, approximately 50% of the polypore species can be considered as strictly or predominantly temperate or Mediterranean, and up to 30% are equally common both in the boreal and temperate/Mediterranean zone (based on data in Ryvarden and Gilbertson 1993; 1994). Only 5% of European polypore species are totally restricted to the boreal zone and approximately 15% are predominantly boreal with scattered occurrences mainly in the mountains of central and southern Europe. Species that predominantly occur in the boreal region, and especially in the continental parts, have been called taiga (Russian expression for boreal conifer forests) species (Eriksson, 1958; Ryvarden, 1993a, 1993b). The majority of taiga species prefer coniferous hosts—which primarily occur in the boreal and mountainous regions—and a large number of them are also brown-rot fungi (Gilbert-son, 1980, 1981). Brown-rot fungi are more efficient in obtaining energy from wood for growth and reproduction than white-rot fungi and, hence, better suited for cold and dry habitats with a short growing season (Gilbertson, 1980). Ryvarden (1993a, 1993b) speculated that the restricted distribution of 'taiga-species'

Table 2 Examples of boreal and boreal/temperate polypore species showing restricted distribution patterns

Distribution of species

Examples of species

Endemic to Europe

Endemic to Asia

Endemic to North America

Eurasian species

European-North American species

Oligoporus septentrionalis Oxyporus borealis Phellinus populicola Postia luteocaesia Sistotrema albolutea Anomoporia vesiculosa (temperate) Antrodiella gypsea (temperate) A. ussurii (temperate) Castanoporus castaneus (temperate) Ceriporiopsis cremea Daedaleopsis sinensis (temperate) Nigroporus ussuriensis (temperate) Oxyporus bucholtzii (temperate) Perenniporia maackiae (temperate) Polyporus choseniae Poriodontia subvinosa (temperate) Rigidoporus camschadalica Spongipellis sibirica Echinodontium tinctorium Ganoderma oregonense Hapalopilus mutans (temperate) Inonotus glomeratus Junghuhnia zonata Oligoporus anguliporus Oxyporus nobilissimus Oxyporus similis Perenniporiu ellisiana Phellinus repandus Trichaptum subchartaceum Tyromyces subgiganteus (temperate) Antrodia mellita Antrodia pulvinascens Antrodiella citrinella Ceriporiopsis resinascens Diplomitoporus flavescens Junghuhnia pseudozilingiana Piloporia sajanensis Skeletocutis jelicii S. papyraceae

Heterobasidion annosum sensu stricto Lindtneria trachyspora (temperate) Oligoporus mappus

246 Jan Stenlid et al. Table 2. (Continued )

Distribution of species Examples of species

Oligoporus ptychogaster North American-North East Asian Anomoporia flavissima species

Auriporia aurea

Cryptoporus volvatus (temperate) Ganoderma tsugae (temperate) Oxyporus cuneatus (temperate) P. variegate (temperate) Phellinus vaninii

Trametes conchifer Pil. (temperate)

Source: Gilbertson and Ryvarden (1986, 1987), Ryvarden and Gilbertson (1993, 1994), Nunez and Ryvarden (2000, 2001), Dai (2000) and distributional information from some other relevant literature were used as sources in estimating the distributional pattern of the species. Nomenclature of the species is according to the above sources (excluding Dai, 2000) and Niemela (2005). Predominantly temperate species with scattered occurrences in the boreal zone are indicated.

Table 3 The number of shared and circumpolar polypore species from two datasets collected from Russian Far East (Kamchatka peninsula, Parmasto, 1963; Magadan Area, Kotiranta and Mukhin, unpublished data) and north-eastern China (Fenglin Nature Reserve, Hemiboreal Region, Dai and Penttila, 2006)

Area Number of Percentage in Percentage in Circumpolar sp.

species North America Europe (%)

Russian Far 118 87 94 86

East

North-eastern 153 80 83 76

China

Note: A few species in the datasets (e.g. recently described new species in the genera Antrodiella and Skeletocutis) were omitted from the comparison, since their existence especially in North America could not be reliably identified.

is caused by an adaptation to a lower optimum growth temperature which makes them less competitive, and thus often non-existent, in areas with a warmer climate. According to Ryvarden (1993a) coniferous-living Amylocystis lapponica and Antrodia albobrunnea among polypores, and corticoid Laurilia sulcata and Phlebia centrifuga are good examples of the so-called taiga species. Other polypores showing a restricted distribution in coniferous forest regions with a more continental climate include Antrodia crassa, Diplomitoporus crustulinus, Gloeophyllum protractum, Inonotopsis subiculosus, Piloporia sajanensis, Pycnoporellus alboluteus, Skeletocutis stellae and Trichaptum laricinum on coniferous hosts, and Daedaleopsis septentrionalis, Haploporus odorus, Phellinus populicola and Polyporus pseudobetulinus on deciduous hosts (Gilbertson and Ryvarden, 1986, 1987; Ryvarden and Gilbertson, 1993, 1994).

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