Since 2.5Mabp, under the influence of periodical change of globe orbit and periodical uplift of the Qinghai-Xizang Plateau, the dry and wet periods of climate on the Loess Plateau have occurred alternately, but the general tend of climatic evolution is to drought. The herbage on the Loess Plateau has been thriving since the Quaternary, but xylophyta flourshed during only few periods. The problem of low moisture layer of soil (LMLS) exists in almost all artificial vegetation conditions on the recent Loess Pl...
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