Environmental Effects on Distribution and Composition of Desert Vegetations in Alxa Plateau:I.Environmental effects on the distribution patterns of vegetation in Alxa Plateau

This study aims to provide an analysis of vegetation and environment relationship in the Alxa Plateau of Inner Mongolia,China.Seventy species representing 46 genera and 16 families are collected.The largest families are Leguminosae,Polygonaceae,Gramineae and Compositae,representing 200%,157%,143% and 143% of the total flora,respectively.Phanerophytes and hemicryptophytes are the most abundant life form.Classification of the vegetation is conducted by using two-way indicator species analysis(Twinspan)techniques.There are six vegetation groups,each group and its soil characteristics can be linked to a specific geomorphologic unit.Ordination techniques as detrended correspondence analysis(DCA)and canonical correspondence analysis(CCA)are used to examine the relationship between vegetation and environmental parameters.Analysis with DCA gave results similar to CCA,suggesting that there is a relatively strong correspondence between vegetation and environmental factors.CCA axis 1 is highly associated with organic matter,total nitrogen,silt and clay content,elevation,Kira moisture index and relative humidity,and CCA axis 2 shows significant correlation with chlorine,calcium ion,magnesium ion and electrolytic conductivity.The first two canonical axes can explain the 60% causes of the species-environment relationship in the study sites,implying that the environmental factors expressed by these two axes are the key determining the distribution of desert vegetation in study area.Understanding relationships between environmental variables and vegetation distribution in this area helps us to apply these findings in management,reclamation,and development of arid and semi-arid grassland ecosystems.