Summer green forest - Karyokurin

A forest that loses its leaves in the winter due to cold weather (average temperature of the coldest month is below 2°C). It is used to distinguish it from rain-green forests that lose their leaves in the dry season. Summer-green forests are distributed in the cool temperate zone of the Northern Hemisphere and are divided into three parts: East Asia including Japan, North America, and Europe. In all cases, oaks, beeches, and maples are the dominant species. The diversity of species varies greatly depending on the extent of the influence of glaciers during the ice age. The diversity of species increases in the order of Europe, North America, and East Asia, and there are many relict endemic species. In the area from Japan to China and the Himalayas, as well as in North America, there are also relict coniferous forests of Paleogene to Neogene periods such as hemlock and cypress. In the Southern Hemisphere, deciduous forests of Antarctic beech are distributed at the southern tip of South America, but they are localized and do not form vegetation zones like in the Northern Hemisphere.

The structure of the forest is such that the trees reach a height of 30 meters, and the tree, shrub, and herbaceous layers are clearly separated. Here, semi-subterranean plants (plants whose dormant buds are in contact with the ground surface during the period when they are not suitable for life) account for 50% of the species.

[Masahiko Osawa]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

冬期に寒冷（最寒月の平均気温が2℃以下）で落葉する林。乾期に落葉する雨緑林と区別するときに使う。夏緑林は北半球の冷温帯域に分布し、日本を含む東アジア、北アメリカ、ヨーロッパの3部分に分けられる。いずれもナラ類、ブナ類、カエデ類が主要優占種である。氷期の氷河の影響の大きさによって、種類的な多様性は大きく異なる。ヨーロッパ、北アメリカ、東アジアの順に種の多様性は高くなり、遺存固有種も多い。日本から中国、ヒマラヤにかけた地域や北アメリカには、ツガ、ヒノキなどの古～新第三紀の遺存型針葉樹林も分布する。南半球では、南アメリカの南端にナンキョクブナの落葉樹林が分布するが局在し、北半球のように植生帯をつくることはない。

　林の構造は樹高30メートルに達し、高木層、低木層、草本層が明瞭(めいりょう)に分けられる。ここでは、半地中植物（生活に不適な時期を越す休眠芽が地表面に接している植物）が種数の50％を占める。

［大澤雅彦］

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