Character of Warm-Temperate Quercus Forests in Asia

The concept of warm-temperate deciduous forest was re-proposed, from mid-temperate forest (Mid-Zone of Tanaka 1887), by Kira (1949, 1991, 2011), based on climatic data and values of his Warmth and Coldness Indices. T. Suzuki (1966) recognized this as the intermediate-temperate zone (Tsugion sieboldii). What kind of forests are warm-temperate forests in Asia? This chapter treats deciduous forests in eastern Asia, especially deciduous Quercus forests, and compares them, based on forest composition and climate data, with more typical temperate and cool-temperate Quercus forests. Quercus serrata forests, in most of eastern Asia, occur in drier, warmer climates than do Fagus forests and in climates that are colder in winter than the evergreen forest area. In Japan such forests are composed mainly of deciduous Quercus serrata, Q. acutissima, Q. variabilis, Castanea crenata, Carpinus tschonoskii, and C. laxiflora. This kind of forest occurs mainly as secondary forest preceding evergreen broad-leaved forest, in both Japan and Korea. Q. serrata and Q. variabilis forests occur naturally and secondarily in Korea and China too, the latter in particular as natural forest in Chinese protected areas. In Japan there is a natural Quercus serrata forest region in inland Honshū, around Nagano and Ueda, as mentioned by Kira (1949) and described by Wada (1977, 1982a, b). We compared these drier, warmer deciduous Quercus forests with Quercus forests in cooler climatic zones, dominated mainly by Q. mongolica var. crispula, Q. mongolica, and Q. wutaishanica. As a result, it appears that Quercus forests can be classified into ten forest types (see main text), which can be grouped into three broader forest classes: (1) warm-temperate forests, with Q. serrata, Q. brevipetiolata Q. variabilis, Q. acutissima and Q. aliena; (2) temperate forests, with Q. mongolica var. crispula and Q. dentata in Japan, Q. mongolica in the Beijing area and southern Chinese Manchuria, and Q. wutaishanica in drier southern Inner Mongolia and the northern Qinling Mts.; and (3) cool-temperate forests, especially mixed forests of Q. mongolica and conifers (Pinus koraiensis, Abies holophyla and A. homolepis) on the Asian mainland (China, Korea and Russia), plus Q. mongolica var. crispula and Abies sachalinensis in Japan. Under human impact, species from the warm-temperate Quercus serrata and Q. variabilis forest invade both the cooler Quercus mongolica and Q. mongolica var. crispula forest in China, Korea and Japan and the warmer evergreen broad-leaved forests in Japan and Korea. Potential natural sites of Q. serrata and Q. variabilis forest in East Asia are subject to laurophyllization, i.e. invasion by planted evergreen species, but laurophyllization from Quercus serrata forests to Q. mongolica forests does not occur in China. Q. variabilis forests occur in areas much drier than those of Q. mongolica and evergreen broad-leaved forests. Conclusions: (1) Quercus serrata and Q. variabilis forests are the main warm-temperate forests in East Asia; and (2) these species also invade as secondary elements into both temperate (deciduous) forests and warm-temperate evergreen broad-leaved forests in East Asia. Similar laurophyllization also occurs in western Mediterranean areas with good soil, where evergreen broad-leaved species invade Quercus pubescens forests, especially in Insubria (southern low slopes of the European Alps) and near the glacial lakes. (3) These warm-temperate forests can be characterized by values of the Warmth and Coldness Indices and an annual moisture index (Box and Fujiwara 2013 and herein).