黄土高原上水热自东南向西北有规律递减,在旱中生和中旱生植物组成的草甸草原背景上,稀疏的分布着一些旱中生矮乔木,称疏林草原,这类群落乔木覆盖度一般不超出20%,通常10%左右,有时低于5%.大致420—520mm 隆水量是决定黄土高原森林草原存在的主要因素.
The Loess Plateau is situated at 33°3′-40°6′N,100°5′-114°3′E. It is covered with loess of 50-150 m thick. As it is eroded by flowing water for a long time,it formed alone yuan,beam-ridges and hill-gullies topography. Humidity and heat decrease gradu-ally from southeast to northwest in the Loess Plateau. The forest is replaced by the steppe, and an obvious transition zone formed between them, it is a forest steppe. Its characteristic is that stunted exro-mesophilous trees are distributed sparsely on the meadow steppe. The meadow steppe mainly consists of xero-mesophytes and meso-xero-phytes,the trees cover degree is usually less than 20%,generally about 10%,sometimes below 5%. Precipitation of about 420-520 mm is a decisive factor of the existence of the forest-steppe in the Loess Plateau.
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