Biogeographical Study of Japanese Beech Forests Under Diffe- Rent Climatic Conditions

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Ber. d. Reinh.-Tüxen-Ges. 20, 179-194. Hannover 2008

Biogeographical study of Japanese beech forests under different climatic conditions

- Yukito Nakamura, Tokyo -

Abstract The Fagetea crenatae are endemic in the Japanese Archipelago and compromise two con- trasting alliances on the Japan Sea side and the Pacific side. Here we show that this distribution pattern is not just caused by the actual environmental differentiation but also results from its synchorological vegetation history. The European Fagetalia sylvaticae are diverse due to continental glaciations. It shares species with the Vaccinio-Piceetea, Rhamno-Prunetea and Galio-Urticetea. The Japanese Saso-Fagetalia crenatae has its own forest species and is clearly distinct from other classes. The long south-north chain of the Japanese Islands functioned as a bridge facilitating migration and isolation of forest species during the glacial age. The Sasamorpho-Fagion crenatae on the Pacific side is vicarious to continental China and Taiwan. By contrast, the Saso kurilensis-Fagion crenatae on the Japan Sea side is characterized by newly evolved species of the Camellietea japonicae, which adapted to the heavy-snow climate which became established in the interglacial period of the Pleistocene.

1. Introduction Fagus is one of the most important canopy trees in the temperate forests of the Northern Hemisphere. There are about 10 species found in regions with mild, humid, oceanic climates (Fig. 1). Along the eastern coast of North America Fagus grandifolia forests belong to the Querceto-Fagetea grandifoliae Knapp 1957 ex Okuda 1994 (KNAPP 1957, 1965, OKUDA 1994). In Eurasia beech has two distribution regions: Eastern Asia and Europe. Fagus sylvatica is a species characteristic of the European Fagetalia sylvaticae. F. crenata and F. japonica are species of the Japanese order of Saso-Fagetalia crenatae. The American Querceto- Fagetea grandifoliae, the European Querco-Fagetea and the Japanese Fagetea crenatae belong to the Querco-Fagea. The two Eurasian classes share taxa such as Milium effusum and Gali- um odoratum, but most of the component taxa are not the same because of different geological events such as global climatic change and isolation of the vegetation territories. The geographical distances of the habitats are proportional to their period of isolation. In two different regions the proportion of common taxa, related taxa (var. & subsp.) and vicarious taxa of the plant communities depend on their geographical distance. In general, vegetation differentiation results from niche segregation which developed as a result of global environmental changes. There were three big geological events in Japanese Archipelago. BP. 25Mln the Arcto-Ter- tiary flora advanced southward to low latitudinal regions. Until BP. 18Mln Fagus antipofi, Castanea, Cercidiphyllum, Ulmus, Aesculus, Acer, Alnus, Betula, Pterocarya, Stewartia, Metasequoia, Tsuga, Pseudotsuga, Picea and others of the so-called Aniai-type flora were characteristic, but as from 18Mln to 14.5Mln it became warmer. The expanded ocean divided the Japanese Archipelago and a warm current emptied into the Japan Sea. This resulted in the Daijima-type flora in which Cinnamomum, Elaeocarpus, and evergreen Quercus are diagno-

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Fig. 1: Distribution of Fagus species. stic. The Mitoku-type flora in the late Miocene to Pliocene shows a cold climate, because of the closing of Tsushima-sea trail (TANAI 1961), and contains species such as Fagus plae- ocrenata, Castanea miocrenata, Quercus protoserrata, Betula miomaximowicziana. In the middle Pliocene the Japanese Archipelago got its present form and through the Tsushima-sea trail a warm current emptied into the Japan Sea again. In this period the Japan Sea side became wet and Metasequoia and Nyssa dominated in the lowlands. Around BP. 0.6Mln the warm sea-current led to a heavy snow climate, the so-called Japan Sea-climate on the mountains of the Japan Sea side. It is hypothesized that the Palaeo vegetation of the Fagetea crenatae is based on the Arcto- Tertiary flora of about BP. 25Mln, and through the orogenic movement the basic form of the Japanese Archipelago was established and the Fagetea crenatae became isolated from continental China in the Miocene. In the interglacial epoch of the Pleistocene the warm sea-current reaching the Japan Sea through the open Tsushima-sea trail caused a heavy snow climate on Japan Sea side. As a result the Fagetea crenatae induced the differentiation of the Sasamor- pho-Fagion crenatae and the Saso kurilensis-Fagion crenatae.

2. Materials Historical events such as global climatic and geological change conduces the differentiation of plant communities. Comparing phytosociological tables of different regions of beech forests with Japanese ones, we discuss the component taxa from a geographical point of view. The following regions are selected: Hannover/Germany, Huangshan/China, Taipin-shan/Tai- wan, Nagano/Japan Sea side and Yamanashi/Pacific side of Japan.

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3. Results Present beech forests occur mainly in Europe and westernmost Asia, eastern North Ame- rica and East Asia. The species composition of the beech forests is based on the Arcto-Terti- ary flora. In comparing the three territories geographical patterns should be found. European beech forests are classified into the Fagetalia sylvaticae Pawlowski in Pawlowiski, Sokolo- wski et Wallisch 28. The North American beech forests are classified into the Querceto-Fage- tea grandiflorae Okuda 1994. Common genera among the Japanese Saso kurilensis-Fagetalia crenatae Suz.-Tok. 1966, the Querceto-Fagetea grandiflorae and the Fagetalia sylvaticae are Fagus, Quercus, Euonymus, Acer, Sorbus, Prunus, Tilia, Fraxinus, Cornus, Viburnum, Car- pinus, Corylus, Polygonatum, Hepatica, Asarum, Actaea and Prenanthus (OBERDORFER 1992, LOHMEYER 1951, OKUDA 1994; RIVAS-MARTINEZ et al. 2002). The flora of the eastern part of North America and Japan is similar (GRAY 1846). Component elements of American beech forest are closer to Japanese beech forest than to the beech forests of other areas. Common genera in both regions are Ostrya, Hydrangea, Callicarpa, Lindera, Hama- melis, Rhododendron, Magnolia, Smilax, Trillium and Disporum. American beech forests are classified into two groups (OKUDA 1994). Northern regions such as Ontario, Quebec, Nova Scotia in Canada and Maine, New Hampshire, Pennsylvania, New York and Massachusetts in the USA are vicarious to the Japanese cool-temperate beech forests. The southern regions such as Appalachian Mountains and Piedmont area, however, are characterized by a flora which is found in fossils of the Miocene in Japan (HOTTA 1974). Representative genera are Carya, Nyssa, Liriodendron and Liquidambar, and these also occur in the subtropical/warm- temperate zone of Eastern China (SONG 2001, NAKAMURA et al. 2004). It seems that the beech forest of the southern type became extinct in Japan. The leaf assemblage from the Seto porcelain clay formation of the late Miocene shows extinct species such as Metasequoia japonica, Liquidambar miosinica, Nyssa pachycarpa, Carya striata, C. ovatocarpa, Fagus stuxbergii, F. palaeojaponica (MIKI 1941, OZAKI 1991). In comparison, the European beech forests (Tab. 1) show three associations of beech forests in Hannover of which the Galio odorati-Fagetum has the same or vicarious species as Japanese beech forests. Galium odoratum, Milium effusum, Maianthemum biflorum, Adoxa moschatellina and Moehringia trinervia are the same. We consider these the continental element, and these species are found mostly in the inland side of central Japan, in the so-called subcontinental climate where Quercus crispula forests are dominant. Fig. 2 shows the syntaxonomical element values calculated from the phytosociological tables. The component species of Japanese beech forests are more than 85% Fagetea crenatae species. However in Hannover beech forest are composed of 35 to almost 60 % with forest species. Other elements consist of species of fringe communities such as the Rhamno-Prunetea, Galio-Urticetea and Artemisietea vulgaris. In Europe, during the ice-age, the continental glacier eradicated the forest species all the way down to the Alps, but in Japan and Taiwan the archipelagos were like a bridge of migration of vegetation. Fagus hayatae is found in Japan in the Elbe Ice Age (HOTTA 1974), but presently Fagus hayatae forest which contains many evergreen species and some common species such as Pourtiaea villosa, Viburnum erosum and Hydrangea paniculata, is a relict in Taiwan (Tab. 2). In eastern Asia, China has three common beech species, Fagus engleriana, F. longipe- tiolata and F. lucida. Chinese Beech forests occur in the subtropical/warm-temperate zone as in Taiwan, and the forests are mixed with evergreen species (NAKAMURA et al. 2004, WANG et al. 2005). The Chinese Aceri davidii-Fagion lucidae occur under warmer climatic conditions in comparison to Japanese beech forests. The Warm-Indices of Chinese beech forests are 70-90 ºC/month and 45-85 ºC /month in Japan (WANG et al. 2005). At Mt. Huangshan/Anhui Province, Chinese beech forests are related to the Japanese Sapio japonici-Fagetum crenatae of the Sasamorpho-Fagion crenatae or the Styraco shiraianae-Fagetum japonicae of the Car-

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Table 1: Summergreen broad leaved forests mixed with beech, Fagus sylvatica in Hannover (LOHMEYER 1951) a: Betulo-Quercetum roboris R. Tx. (1927) 1937 b: Galio odorati-Fagetum Sougnez & Till 1959 em. Dierschke 1989 c: Stellario holosteae-Carpinetum betuli Oberd. 1957

Spalte: a b c Anzahl der Aufnahmen in der Originaltabelle: 15 49 18 Mittlere Artenzahl: 21 22 26 Kenn- u. Trennarten d. Ass.: Dryopteris austriaca ssp. spinulosa IV(+-2) . . Frangula alnus IV(+-2) I (r-3) . Polytrichum attenuatum IV(+-2) r (+) . Pinus silvestris IV (2-3) . . Molinia coerulea III (1-2) . . Dryopteris austriaca ssp. dilatata II (+-2) . . Betula pubescens III (+-2) r (+) + (+) Agrostis capillaris III (+) . . Mnium hornum II (1-2) . . Betula pendula II (+-1) . . Brachythecium rutabulum II (+-2) . I (+-2) Mnium affine III (+-3) . . Festuca silvatica III (+-3) IV (+-4) . Galium odoratum +(1) III (+-3) . Moehringia trinervia I (1) II (+-1) . Convallaria majalis +(1) II (+-5) . Melica uniflora . II (+-4) . Festuca gigantea . + (+) . Carex remota . + (+-1) III (+-2) Arum maculatum . II (+-2) III (+-2) Euonymus europaeus . I (+-1) III (+-2) Cornus sanguinea . r (+) III (+-3) Crataegus oxyacantha . + (+) II (+-2) Ranunculus repens . . II (+-1) Equisetum hiemale . . II (+-4) Geum rivale . . I (+-2) Sonstige Arten: Quercus robur III (+-4) V (+-5) IV (+-4) Carpinus betulus II (+) IV (+-4) IV (+-4) Milium effusum 5 (+-3) V (+-3) IV (+-3) Rubus idaeus III (+-1) II (+-1) II (+-2) Rubus spec. 5 (1-4) III (+-3) I (1-2) Sorbus aucuparia 5 (1-4) III (+-3) II (+-4) Anemone nemorosa l (+-2) V (1-4) III (+-4) Hedera helix I (+) V (+-4) IV (+-3) Fagus silvatica III (+-1) V (+-5) I (+-2) Poa nemoralis II (+-1) II (+-2) II (+-3) Polygonatum multiflorum II (+) IV (+-2) II (+-1) Acer platanoides + (+) III (+-4) III (+-2) Acer pseudoplatanus + (+) IV (+-3) II (+-3) pino-Quercion serratae on the Pacific side (NAKAMURA et al. 2004). Taxa common to the Japanese Sapio japonici-Fagetum crenatae and the Chinese Sapio japonici-Fagetum englerianae are Lindera obtusiloba, Prunus grayana, Kalopanax septemlobus, Sapium japonicum,

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Fig. 2: Syntaxonomical element values calculated from Phytosociological tables. Hydrangea paniculata, Ilex macropoda, Clethra barbinervis, etc. (Tab. 3). Vicarious species are Sasamorpha sinica (S. borealis), and Stewartia sinensis (S. monadelpha) which are characteristic species of the Sasamorho-Fagion crenatae. In addition Kirengeshoma palmata and Magnolia sieboldii, the so-called Sohayaki-flora element which is characteristic of the Paci- fic side of western Japan, occur in China. That is to say the Sapio japonici-Fagetum crenatae and the Styraco shiraianae-Fagetum japonicae are vicarious to the Chinese Sapio japonici- Fagetum englerianae. Taxonomically F. japonica belongs to same affinity group as F. engleriana (MINAKI & OKAMOTO 1985). Thus we conclude that the oldest beech forest type of Japan that is related to continental China occurs in southwestern Japan on the Pacific side. In contrast, the Saso-Fagion crenatae on the Japanese Sea side is characterized by new endemic species (Tab. 4). In contrast to the Sasamorpho-Fagion crenatae the Saso-Fagion crenatae has in its understory many evergreen shrubs deriving from the Camellietea japonicae. They are

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Table 2: Beech forest in Taiwan Date (2007): 29-Oct Height of tree-layer 1 (m): 18 Height of tree-layer 2 (m): 9 Coverage of tree-layer 1 (%): 70 Coverage of tree-layer 2 (%): 20 Height of shrub-layer (m): 4 Height of herb-layer (m): 1.2 Coverage of shrub-layer (%) 30 Coverage of herb-layer (%) 80 Exposition: NE Elevation (m): ### Graduent: 40 Quadrat size (m2) 15 x 15 Species number: 42 in Japan in Japan Fagus hayatae T1 4.4 Smilax sp. H + Cyrtococcum accrescens H + Dryopteris formosana H 2.2 Viburnumfoetidum var. rect- S + Yushania niitakayamensis H 4.5 angulatum Acrophorus stipellatus H + Carex sp. H 1.2 Viburnum erosum S 2.3 o Oxalis griffithii var. formosana H 1.1 Viburnum sympodiale S 1.1 o Asarum macranthum H + Symplocos arisanensis S 1.2 Elatostema sp. H 1.2 Symplocos arisanensis H +.2 Plagiogyria formosana H 1.2 Neolitsea acuminatissima S + Salvia sp. H + Neolitsea acuminatissima H + Viola formosana H 1.2 Hydrangea paniculata S + o Rubus pungens var. oldhamii H + Illicium anisatum S + Arachniodes sp. H + Pourthiaea villosa var. S 2.3 o Ardisia japonica H +.2 parvifolia Litsea elongata var. S + Selaginella remotifolia H + mushaensis Lepisorus sp.-1 H +.2 Rubus corchorifolius H + Lepisorus sp.-2 H + Tripterospermum taiwanense H +.2 Acer palmatum var. pubescens H + o Sarcopyramis nepalensis var. H 1.2 bodinieri Pellionia radicans H + Ardisia crenata H + Arachniodes rhomboides var. H + Dendropanax dentiger H + yakusimensis Lithocarpus hancei H + Damnacanthus angustifolius H + Eurya crenatifolia H 1.2 Stauntonia obovatifoliola H +.2 Plagiogyria rankanensis H +.2 Schizophragma integrifolium H +.2 o var. fauriei

morphologically adapted to the deep snow cover protecting from the coldness as shown. e.g., by their nano-form. Camellia japonica is a sub-tree and its height is less than 12m, but subsp. rusticana is prostrate and reproduces vegetatively. Aucuba japonica var. borealis differs from A. japonica of the Camellietea japonicae. Similarity, Ilex leucoclada differs from I. integra, I. crenata var. paludosa, as well as Daphniphyllum macropodum var. humile and Cephalota- xus harringtonia var. nana from their elementary taxa (Tab. 5). Dwarf Sasa species such as S. kurilensis, S. palmata, S. megalophylla and S. senanensis need a snow depth of more than 75 cm for the protection of their buds (SUZUKI 1961). They have also withy stems against the snow pressure. In the montane belt of the Pacific side the mean snow depth is less than 50cm. Here Sasa nipponica is a characteristic species of the Sasamorpho-Fagion crenatae. It forms its buds at the soil surface and does not need deep snow for its protection. Sasamorpha borealis, however, a character species of the Sasamorpho-Fagion crenatae, is even cold tolerant, and forms its buds at the height of more than 1m. Sasamorpha borealis is a vicarious species

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Table 3: Chinese Beech forests Sapio japonici-Fagetum englerianae Height of tree layer TI(m): 15 13 Height of tree layer T2(m): 9 Coverage of tree layer TI(%): 70 70 Coverage of tree layer T2(%): 20 Height of shrub layer S(m): 3 4 Height of herb layer H(m): 1.2 Coverage of shrub layer S(%): 50 40 Coverage of herb layer H(%): 80 Aspeet & Slope: SE2 20 Altitude (m): 1460 0 Ch. & Diff. species of ass.: Vicarious to in Japan Fagus engleriana T1 3.2 4.3 Pacific Ocean-side T2 + . H . +.2 Sapium japonicum S 1.2 1.2 o Prunus grayana S + +.2 o Viburnum simpodeale S 1.1 + Enkianthus chinensis S 2.3 . Amelanchier asiatica S 1.1 . o Sasamorpha sinica H 5.5 . o Sa. borealis Stewartia chinensis T2 . 2.2 o St. monadelpha Symplocos anomala S . 1.1 Magnolia cylindrica T2 . 1.2 S . + Allantodia squamigera H . + Companions: Acer palmatum S + 1.2 o H . + Ainsliaea macroclinidioides H +.2 + o Carpinus fargesii TI . l.1 S 1.1 +.2 Castanea seguinii TI 2.2 l.1 Daphniphyllum macropodum S + 2.3 o Eurya alata S + 2.2 Evodiopanax trifidus S 1.2 1.2 o E. innovans Hamamelis mollis T2,S + ± o H. japonica Ilex macropoda T2,S + ± o Ilex pedunculosa S 1.2 . o H l.1 + Quercus stewardiana T2.S 1.1 1.2 H +.2 . Rhododendron ovatum S 1.1 1.2 H + . Rhododendron simusii S 2.2 2.3 o Schisandra sphenanthera H +.2 +.2 Schoefia jasminodora T2,S + ± o Skimmia revesiana H + + o Sorbus alnifolia T1 . l.1 o S + + Torreya grandis S,H ± + Tripterospermum chinense H +.2 +.2 Viola concordifolia var. ciliata H + +.2 Euscaphis japonicus T2 . l.1 o S,H + ±

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Table 4: Summerized table of beech forests in Central Honshu Community Nr.: 1 2 3 4 Endemic Prefecture: Nagano Nagano Yamanash Yamanash i i Number of stands: 3 13 4 15 in Japan Characteristic & differential species of Camellido-Fagetum crenatae: Aesculus turbinata 3(+-1) +(+) . . o Aucuba japonica var. borealis 3(+-1) +(+) . . o Camellia japonica subsp. rusticana 3(2-4) . . . o Lindera praecox var. pubescens 2(+-1) . . . o Characteristic & differential species of Hamemelido-Fagetum crenatae: Magnolia salicifolia . IV(+-2) . . o Daphniphyllum macropodum var. humile . IV(+-1) . . o Plagiogyria matsumureana . IV(+-1) . . o Ilex crenata var. paludosa . III(+-2) . . o Mitchella undulata . III(+-1) . . Rhododendron albrechtii . II(+-2) . . o Rhododendron nudipes ssp. niphophilum . II(+-2) . . o Shortia soldanelloides var. magna . II(+-2) . . o Shortia uniflora . II (1-3) . . o Species of Saso kurilensis-Fagion crenatae: Acer mono var. mayrii l(2) III (+-1) . . o Sasa kurilensis 3(1-3) V(+-5) . . o Lindera umbellata var. membranacea 3(1) V(+-3) . . o Cephalotaxus harringtonia var. nana 3(+-1) IV(+-2) . . o Acer palmatum var. matsumurae 3(1-2) IV(+-2) . . o Vaccinium japonicum l(+) III(+-2) . . Ilex leucoclada l(+) IV(+-1) . . o Hamamelis japonica var. obtusata l(+) II(1-2) . . o Carex foliosissima l(3) II(1-2) . . o Characteristic & differential species of Fagetum crenato-japonicae: Meliosma myriantha . . 4(+-2) . Acer tenuifolium . . 3(1) . o Lindera obtusiloba . . 3(+-1) . Acer mono var. marmoratum . . 3(+-1) . Schisandra repanda . . 3(+) . Hydrangea scandens . . 3(+-1) . o Stephanandra incisa . . 3(+) . Clinopodium gracile var. multicaule . . 2(+) . Characteristic & differential species of Corno-Fageteum crenatae: Acer micranthum . . . IV(+-1) o Rhododendron wadanum . . . IV(1-3) o Pieris japonica . . l(+) III(+-2) o Abies homolepis . . . III(+-1) o Enkianthus campanulatus . . . III(+-3) o Hamamelis japonica . . . II(+-2) o Stewartia pseudo-camellia . . . II(+-1) o Species of Sasamorpho-Fagion crenatae: Sasa borealis . . 4(2-4) V(1-5) o Tsuga sieboldii . . 3(+-2) IV(+-4) o Rhododendron semibarbatum . . 3(+) II(+-3) o Fagus japonica . . 3(2-3) IV(+-4) o Rhododendron dilatatum . . 3(+-2) II(1-3) o Acer plamatum var. amoenum . . 3(+-1) I (+-1) o Hydrangea hirta . . 3(+) II(+-1) o Abies firma . . 3(+-1) II(+-2) o Fraxinus sieboldiana var. pubescens . . l(1) II(+-2) o Species of Fagetea crenatae: Fagus crenata 3(2-4) V(2-5) 4(+-3) V(1-5) o Quercus crispula 2(3) III(+-5) 4(+-1) IV(+-5) o Clethra barbinervis 2(+) IV(+-3) l(1) V(+-3) o Acer japonicum 3(+) V(+-2) . IV(+-3) o Fraxinus lanuginosa 2(+) IV(+-2) 4(+) III(+-1) o Viburnum furcatum l(+) V(+-2) . III(+-2) o Acer sieboldianum l(+) II(+-1) 3(1) IV(+-2) o Schizophragma hydrangeoides 3(+-1) IV(+-1) l(+-1) II(+) o

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Table 5: Distributional pattern of understories of beech forests in different climatic regions Pacific Japan Sea-side Ancestor Ocean-side Dwarf bamboo: Sasa nipponica o - Sasa hayatae o - Susamorpha borealis o - Sasa kurilensis - o Susa palmata - o Sasa senanensis - o Sasa megalophylla - o Evergreen shrub: Aucuba japonica var. borealis - o Aucuba japonica Camellia rusticana - o Camellia japonica Ilex leucoclada - o Ilex integra Skimmia japonica var. repens - o Skimmia japonica Daphniphyllum humile - o Daphniphyllum macropodum Cephalotaxus harringtonia var. - o Cephalotaxus harringtonia nana Summergreen shrub: Acer palmatum var. amoenum o - Acer palmatum var. matsumurae - o Lindera umbellata o - Lindera membranacea - o Lindera umbellata Hamamelis japonica o - Hamamelis japonica var. obtusata - o Hydrangea serrata o - Hydrangea serrata var. megacarpa - o Ilex geniculata o - Ilex geniculata var. glabra - o Stewartia monadelpha o - Symplocos coreana o - Magnolia salicifolia - o Rhododendron albrechtii - o of S. sinica and occurs in the understories of deciduous forests such as Quercus stewardiana and Fagus engleriana forests in the montane belt of Eastern China (Tab. 3).

4. Discussion Temperate summer-green broad-leaved forests in the northern hemisphere, in particular beech forests, develop in the maritime regions under oceanic climate conditions. The beech forests of eastern North America, Europe and East Asia are classified into the Querco-Fagea and the common genera of this class group are Carpinus, Corylus, Ostrya, Fagus, Quercus, Castanea, Ulmus, Euonymus, Rhododendron, Viburnum, Aesculus, Acer, Tilia, Fraxinus, Amelanchier, Cornus, Maianthemum, Polygonatum and Tsuga. The beech forests of Eastern China and Taiwan are vicarious to the Japanese Sasamorpho-Fagion crenatae (Figs. 3, 4). The Japanese beech forests are clearly distinct from the warm temperate evergreen forests, the Camellietea japonicae. The physiognomy and species composition are more like the Europe- an or North American beech forests. The common environmental characteristic is the oceanic climate in the temperate zone and this also is the main environmental factor for the Fagetea

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Fig. 3: Similarity of plant communities, genus-level (DCA analysis). crenatae (Fig. 5). Endemism in the Fagetea crenatae was brought about by the geological events in the Miocene. Many fossil plants of the late Miocene, 9-8Ma, are vicarious to present species. Fagus stuxbergii (Nathorst) Tanai is similar to F. crenata and F. palaeojaponica Tanai & Onoe to present F. japonica (OZAKI 1991). However, characteristic new endemic species of the Saso kurilensis-Fagion crenatae, such as evergreen shrubs, did not appear until the Japan Sea climate developed during the Pleistocene. Presently the Fagetea crenatae are very rich in isolated endemic species, which together add up to more than 85% of the total

Fig. 4: Similarity of plant communities, species-level (DCA analysis).

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Fig. 5: Bioclimatic map of East Asia (KRESTOV 2006).

Fig. 6: Paleogeographical maps of Mindel (A) and Riss (B) glacial ages (MINATO & IJIRI 1976).

189 ©Reinhold-Tüxen-Gesellschaft (http://www.reinhold-tuexen-gesellschaft.de/) characteristic species in central Honshu (Tab. 4). It seems that the Miocene beech mixed forests looked like the Sasamorpho-Fagion crenatae. Mitochondrial DNA variation in Fagus crenata shows three phylogeographic patterns (TOMARU et al. 1997, 1998). Pattern I is similar to the distributional area of the Saso kurilensis-Fagion crenatae. Pattern II is similar to the Sasamorpho-Fagion crenatae in Kii, Kanto and southern Tohoku on Honshu. Pattern III is similar to the Sasamorpho-Fagion crenatae in Chugoku, Shikoku and Kyushu. Allozyme variation of Fagus crenata is homogenous in the

Fig. 7: Distribution of beech forests-1 (NAKAMURA 1990).

Fig. 8: Distribution of beech forests-2 (NAKAMURA 1990).

Fig. 9: Distribution of beech forests-3 (NAKAMURA 1990).

Japan Sea side until southern Hokkaido, and in contrast to the Pacific side (TOMARU 1997, 1998). In the Pleistocene interglacial period, in response to the glacio-eustatic sea-level change, the Tsushima-sea trail was opened, and then the warm current emptied into the Japan Sea and a heavy-snow climate, so-called Japan Sea climate, became established (Fig. 6). As a result the Saso kurilensis-Fagion crenatae spread out in a short period. This is thought to explain why the allozyme variation of Fagus crenata is homogenous on the Japan Sea side. But it is heterogeneous on the Pacific side. A corresponding finding is that the Sasamorpho- Fagion crenatae is also more diverse. During the glacial periods Pacific beech forests had suf- ficient time to differentiate and this occurred as a result of isolation in refugia. The evolution of beech forests in Japan is summarized as follows: Querco-Fagea (Arche- type) contained the Arcto-Tertiary flora, and spread southward. The Fagetea crenatae (Archetype) became established under the oceanic climate in the cool temperate zone and was isolated in the Japanese Archipelago at the late Miocene. The Saso-Fagetalia crenatae (Archetype) and Sasamorpho-Fagion crenatae (Archetype) developed as a result of orogenic movement. In the interglacial periods of the Pleistocene the warm sea current created the heavy snow climate on the Japan Sea side and the Saso kurilensis-Fagion crenatae became established (Figs. 7-9).

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Prof. Dr. Yukito Nakamura, Tokyo University of Agriculture, Sakuragaoka 1-1-1, Setagaya- ku, Tokyo 156-8502, Japan [email protected]

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