Effect of Forbidden Pasturing on Biomass of Different Degraded Degree Grassland in Area of Yollow River Source

The change of above-ground and under-ground biomass in different degraded degree grassland was studied after forbidder pasturing four years in the area of Yellow River source,The results showed that total above-ground and under-ground biomass in the region of forbidden pasturing were lower than those in grazing land for non-degraded grassland(P0.05).The total above-ground and under-ground biomass in the region of forbidden pasturing were significantly higher than those in grazing land for moderately degraded grassland(P0.05).The total biomass in the heavily and extremely degraded grassland was the increase tend afrer forbidden pasturing(P0.05).There was the increase tend in the above-ground biomass of grasses and sedges(P0.05 in moderately degraded grassland,P0.0.5 in other),and the decrease tend in the total biomass of forbs for all grassland(P0.05) after forbidden pasturing.The ratio of under-ground biomass to above-ground biomass in the region of forbidden pasturing was lower than that in grazing land for non-degraded grassland(P0.05),but the one increased for moderately,heavily and extremely degraded grassland(P0.05).