Analysis of the Plant Individual Behaviour During the Degradation and Restoring Succession in Steppe Community Mechanism of Degradation Succession in Leymus chinensis+Stipa grandis Steppe Community Morphological Plasticity and the Biomass Allocation Models of Miniaturized Leymus chinensis EFFECTS OF GRAZING ON FOLIAGE BIOMASS ALLOCATION OF GRASS-LAND COMMUNITIES IN XILIN RIVER BASIN, INNER MONGOLIA