Early Warning Indicators Of Grassland Degradation In Three Steppes Ecosystems In Inner Mongolia

Grassland degradation is more and more serious in recent years.And 90 percent of grassland degradation can be attributed to overgrazing.Continuous grazing leads to obvious spatial heterogeneity in family rangeland in Inner Mongolia.Restoration of degenerated grassland is very time consuming and needs a lot of money.Therefore,the early warning indicator of grassland degradation can be considered as an important theoretical basis for grassland management and grassland degradation.There are three types of steppe in Inner Mongolia: Stipa baicalensis meadow steppe,Stipa grandis typical steppe and Stipa breviflora desert steppe.Representative samples were selected in each type.Plots were classified into light(L),moderate(M)and heavy(H)grazing intensities based on preliminary investigations of vegetation in 2004 and the cluster analysis,which corresponded with the distances from the centre points.An enclosure area that had not been grazed near family ranch was chosen to be the control plot.Vegetation investigation was applied under 4 grazing intensities and continued five consecutive years in three difference steppe types.This research studied the effects of grazing on plant community composition,further explored the early warning indicators of grassland degradation by early warning model.The results showed that:(1)In Stipa baicalensis meadow steppe,with the increase of grazing intensity aboveground biomass decreased;in Stipa grandis typical steppe,aboveground biomass in CK plot was significant higher than other grazing plots,however there was no significant difference among the other three grazing intensities;in Stipa breviflora desert steppe,aboveground biomass decreased as grazing intensity increased only in wet year.(2)In Stipa baicalensis meadow steppe,relative biomass of perennial forbs reduced when grazing intensity increased,while annuals/biennials and perennial rhizomatous grasses showed opposite trend;in Stipa grandis typical steppe,relative biomass of perennial rhizomatous grassesand perennialbunchgrasses declined;while shrubs and annuals/biennials and perennial forbs arised following the grazing intensity gradient;in Stipa breviflora desert steppe,relative biomass of perennial rhizomatous grasses,bunchgrasses and shrubs/semi-shrubs decreased,while annuals/biennials and perennial forbs increased.(3)Leymus chinensis and Stipa plant relative biomass were reduced with the increase of grazing intensity;Cleistogenes plant had highest relative biomass in moderate grazing intensity;Artemisia frigida had highest relative biomas under heavy grazing intensity.(4)In Stipa baicalensis meadow steppe,native community dominated by perennial bunchgrass was transited to degradation community that dominated by perennial forbs.The relative biomass of perennial forbs was more than60% in degeneration community,that was the early warning indicator of Stipa baicalensis meadow steppe.In Stipa grandis typical steppe,native community dominated by perennial bunchgrass was transited to degradation community that dominated by perennial forbs.The relative biomass of perennial forbs was above 44% in degeneration community,that was the early warning indicator of Stipa grandis typical steppe.In Stipa breviflora desert steppe,native community dominated by perennial bunchgrass was transited to degradation community that dominated by shrubs/semi-shrubs and perennial forbs.The relative biomass of shrubs/semi-shrubs was more than 33%,and the relative biomass of perennial forbs was more than 28% in degeneration community,that was the early warning indicator of Stipa breviflora desert steppe.