| Summary: | In Midelt high plain, alfa (Stipa tenacissima L.) is formed by mean to high density good state of health and tall tufts that can sometimes reach up to 1.2 m height. It there builds up a spontaneous steppic intramountain ecosystem, characterized by a good regeneration that attests topo-edapho-climatic conditions are favorable to its growth and reproduction. Climatic approach used for characterizing this plain steppe (in contrast with slope steppe) is based on two climatic criteria: raininess (and more generally rainfalls) and temperature. Each of these two parameters has been analysed from different points of view using different indicators. These criteria are not the only climatic factors that act on the life conditions of alfa and its accompanying steppic vegetal species; but they are predominant. Indeed, these factors have close correlations with other climatic parameters such as relative humidity, wind and insolation. Finally, the P/2T ratio of H. GAUSSEN has been used to delimit the modalities of dryness.
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