©Reinhold-Tüxen-Gesellschaft (http://www.reinhold-tuexen-gesellschaft.de/) Ber. d. Reinh.-Tüxen-Ges. 20, 179-194. Hannover 2008 Biogeographical study of Japanese beech forests under diffe- rent 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 distribu- tion 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 clear- ly 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 sylva- tica is a species characteristic of the European Fagetalia sylvaticae. F. crenata and F. japoni- ca 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 geologi- cal 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 vica- rious taxa of the plant communities depend on their geographical distance. In general, vege- tation 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- 179 ©Reinhold-Tüxen-Gesellschaft (http://www.reinhold-tuexen-gesellschaft.de/) 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 beca- me 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 conti- nental 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 differentia- tion 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. 180 ©Reinhold-Tüxen-Gesellschaft (http://www.reinhold-tuexen-gesellschaft.de/) 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 japo- nica, Liquidambar miosinica, Nyssa pachycarpa, Carya striata, C. ovatocarpa, Fagus stux- bergii, 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 odo- rati-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 crispu- la 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 conditi- ons 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- 181 ©Reinhold-Tüxen-Gesellschaft