Niche differentiation characteristics of plant functional groups ondegraded grassland in the upstream of Shiyang RiverA case study of Heteropappus Altaicus type grassland

The Heteropappus Altaicus type degraded grassland and its original community were studied through spatialtemporal conversion method in the upstream of Shiyang River. Based on investigation of plant functional groups (PFTs) structures, the characteristics of seasonal dynamics were studied. The results indicated that the seasonal dynamics of niche breadth trends depended on the kind of the PFTs, and independent with successional stages which the PFTs belonged to, the niche quantity characteristics were affected by their succession period. During the observation period, gramineous functional group increased by 120.8% in degradation grassland, and 65.5% in nondegraded grassland. The forbs functional groups were different from gramineous functional goups, the niche breadth indexes decreased by 51.38% in degradation grassland, and 66.34% in nondegraded grassland. The niche overlap indexes also depended on the kind of the PFTs, independed on the successional stages. The niche overlap indexes of the GramineousForbs functional groups increased by 113.3% in degradation grassland, and 119.4% in nondegraded grassland with seasonal process, and niche overlap indexes in degradation grassland were lower than nondegraded grassland. The ForbsGramineous functional groups contrary to the Gramineous Forbs functional groups, the indexes of niche overlap decreased by 53.0% and 54.9% according to degraded grassland and nondegraded grassland, and there was a inflection point in the mid of July, before that period, the indexes of niche overlap in GramineousForbs functional groups were higher than ForbsGramineous functional groups. The causes of the phenomena may be associated with growth characteristics of the plant functional groups and grazing disturbing. The gramineous functional group regenerated early in the spring, it was just in the time that livestock graze, the continuous disturbance had an effect on the growth of gramineous functional groups, this effect could provide more resources and spaces to forbs functional groups, so that former functional groups structure changed in different seasons in different grassland. The Heteropappus Altaicus stage was the turning point in the plant community succession, if using the propriety grassland management measures, the degraded grassland could change to a new succession which have high yield and appropriate structure, while if the grassland kept the grazing form as before, the grassland would degraded aggravatingly, which will improve the unknown risk.