The Huan County is situated at the north of the Loess plateau of Gansu eastern. The area is 9 326 km2. The natural vegetation is situated at the regions transition from forest-steppe to desert-steppe. The comparative studies on natural grassland vegetation at 40 years ago and present have been made. Under the influence of nature factor and human activity together

the evolution results of natural grassland vegetation are as follows. The natural distributed original vegetation is replaced almost by secondary vegetation. The vegetation constitute tend to simplify

the formation of arbor and shrub natural grown disappeared. The typical zone formation of stipa brevi-flora

stipa bungeana

and stipa grandis vanished

and some of formation distributed small area faded out. The dominant species of each formation and the ecological characters of vegetation changed

and ecological function reduced. The natural grassland vegetation is serious degeneration

and the main reason caused those is human activities

that is cultivate

felling with axe

and excess graze

not the natural factors.