Cluster Analysis on Change Laws of the Vegetation under Different Grazing Densities in Horqin Sandy Pasture

The results are got by field grazing experiment as follows: ① As the grazing density increases, vegetation coverage, height and forage production decrease obviously, of which degenerated grassland tends to recover under light grazing and the vegetation tends to deteriorate under overgrazing and the vegetation changes with climate change under moderate grazing; ② Perennial plants and palatable annual plants withdraw in succession from grassland and annual plants of poor quality dominate absolutely under overgrazing; Ratio of domination index between perennial plant and annual plant is 2∶3 under no grazing and light grazing; The change of domination plants is slow and domination index ratio between perennial plant and annual plant is 1:4 under moderate grazing; ③ Sandy grassland is very susceptible to disturbance in grazing, obvious change appears in the vegetation as soon as the grassland is grazed. The vegetation changes along individual direction under different grazing densities, and the speed relates to the grazing density, especially to the duration.