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In physical geography, a steppe () is an ecoregion, in the montane grasslands and shrublands and temperate grasslands, savannas, and shrublands biomes, characterized by grassland plains without trees apart from those near rivers and lakes. The prairie (especially the shortgrass and mixed prairie) is an example of a steppe, though it is not usually called such. It may be semi-desert, or covered with grass or shrubs or both, depending on the season and latitude. The term is also used to denote the climate encountered in regions too dry to support a forest, but not dry enough to be a desert. The soil is typically of chernozem type. Steppes are usually characterized by a semi-arid and continental climate. Extremes can be recorded in the summer of up to 40 °C (104 °F) and in winter, –40 °C (–40 °F). Besides this huge difference between summer and winter, the differences between day and night are also very great. In the highlands of Mongolia, 30 °C (86 °F) can be reached during the day with sub-zero °C (sub 32 °F) readings at night. The mid-latitude steppes can be summarised by hot summers and cold winters, averaging 250–500 mm (10-20 inches) of precipitation per year. Precipitation level alone is not what defines a steppe climate; potential evapotranspiration must also be taken into account. ==Two types== Two types of steppe can be recorded:〔(Ecological Subregions of the United States )〕 * Temperate steppe: the "true" steppe, found in continental areas of the world; they can be further subdivided, as in the Rocky Mountains Steppes〔 * Subtropical steppe: a similar association of plants that can be found in the driest areas with a Mediterranean-like climate; it usually has a short wet period Peculiar types of steppe include shrub-steppe and alpine-steppe. The Eurasian Grass-Steppe of the temperate grasslands, savannas, and shrublands had a role in the spread of the horse, the wheel, and the Indo-European languages. The Indo-European expansion and diverse invasions of horse archer civilizations of the steppe eventually led to, e.g., the rise of Mycenaean Greece by amalgamation of Indo-Europeans with the autochthonous pre-Greek population and also its destruction during the Dorian invasion in the Late Bronze Age collapse, followed by the demise of the Achaeans, the spread of the Sea Peoples, and eventually the rise of Archaic and ultimately Classical Greece. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Steppe」の詳細全文を読む スポンサード リンク
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