The Species Hierarchy Classification And Important Value Method Improvement In Grassland Community

Basing on the study of the relationship between the species and its biomass proportions in grassland community,we established the species hierarchy classification method of grassland community,and tested the validity of the method.Using Gini coefficient,we evaluated the equilibrium on species and biomass proportions for the first time.Furthermore,basing on the comparion of the effects of Ar,Br,Cr,Fr,Hr and their combinations on the species important value(IV)calculation,and the evaluation for the error size of species IV calculation in different formulas,we improved the species IV estimation method in grassland community.The results were as follows:According to the relationship of species and biomass proportions,the species in grassland community were divided into the dominant and sub-dominant species,main companion species,secondary companion species and occasional species,and their respective biomass proportions were 55%,25%,19.5% and 0.5%.Their species proportions were 0%~15%,5%~20%,40%~60%and 20%~40% in the community level,and 5%~20%,10%~25%,35%~55% and 15%~35% in the quadrat level,respectively.The species and biomass proportions followed “20-80” rule in the community level,being20% of the species provide 80% of biomass in the grassland;while in the quadrat level it followed“30-80” rule,being 30% of the species provide 80% of biomass.The grassland equilibrium evaluated by Gini coefficient was consistent with the pattern of relationship between species and biomass proportions.The relationship is un-equilibrium under a higher Gini coefficient.For the single relative index,the correlation coefficients between the species IV and their respective CAr(tiller),CBr or CCr were better than those between the species IV and the CAr(plant),CFr or CHr;while for the two relative indices excluding of Ar+Hr and Fr+Hr,and for the three relative indices and the volume,their correlation coefficients were highly significant.In this study,we proposed the resonable threshold in species proportions of dominant andsubdominant species,main companion species,secondary companion species and occasional species in grassland community,and recommended the use of Vr or Cr+Hr in alpine shrubs herb layers and Cr in alpine meadows to estimate the species IV,respectively.