Study On The Community Characteristics And Geographic Distribution Of Stipa Grandis Steppe In China

Stipa grandis is a perennial xeromorphic fasciculate herb,belonging to the family of Poaceae,and its floristic geographical element is Loess Plateau-eastern part of Mongolia Plateau distribution.S.grandis steppe is one of the most representative and widespread vegetation types in the north temperate zone.Its distribution area is an important animal husbandry base and ecological barrier construction area in northern China.The geographical distribution of S.grandis steppe has recognizable zonal characteristics,systematic study on its community characteristics and geographical distribution can provide a scientific basis for the vegetation division of China's grassland,and has important practical significance for the vegetation preservation of S.grandis steppe and the proper arrangements for grazing and livestock production.Based on the systematical understanding of the community characteristics and spatial distribution of S.grandis steppe and the detailed investigation of 120 plots in S.grandis steppe,we obtained the following conclusions:1.Based on the quadrat recorded,229 plants belonging to 39 families and 125 genera?including the subspecies,varieties and forma?were recorded in the S.grandis steppe of China.The main life form is perennial herbs,with 166 species,accounting for 72.49%of all species.As for the Raunkiaer's living form,the hemicryptophytes plants are absolutely dominant,accounting for 63.76%of the total species,with 146 species in total.According to the statistics of water ecological type,xerophyte is the dominant type.There are 133xerophytes species?super-xerophyte,xerophyte and mid-xerophyte?,accounting for 58.08%of the total species,95 species?41.48%?recorded in the mid-xerophyte group,accounting for 41.48%of the total species.According to the statistics of floristic geographical components,there are 157 species?68.56%?recorded in temperate elements?Pan-temperate elements,Holarctic elements,palaearctic elements and East palaearctic elements?.The floristic characteristics fully reflect the temperate nature of the regional geography of S.grandis steppe,and reflect the adaptation of S.grandis steppe to the semi-arid environment from the life type and water ecological type.2.According to the Vegetation Map of China?1:1000000?recorded,S.grandis steppe is distributed in Inner Mongolia,Gansu,Ningxia,Shanxi,Shaanxi,Hebei and Jilin,with a total area of 713700 km².Based on Vegetation Map of China?1:1000000?and CNLUCC?2018?,21.25%of S.grandis steppe habitat has been lost,the main way of habitat loss is from grassland to cultivated land?9.79%?,turn to unused land?6.38%?,turn to forest land?3.16%?.3.20 dominant species were selected according to the frequency and important value of species.Based on the important value-species matrix,the interspecific association analysis was carried out.Pearson's correlation and Spearman's rank correlation test mainly shows negative correlation,with the proportion of 61.05%and 53.68%respectively;?²test mainly shows positive correlation,with the proportion of 46.32%.According to the calculation of overall correlation of the dominant species by variance ratio method,the results show that,based on the analysis of the important values-species matrix,the results show significant negative association,which indicates that the important values relationships of the dominant species vary greatly between sample plots.Based on the analysis of the binary data,the results show no significant positive association,which indicates the dominant species composition is relatively stable.4.120 plots of S.grandis steppe are divided into 9 association group and 98association by the dominant species classification method.This plots also can be divided into 7 groups by UPGMA method,and 16 groups at the fourth level of classification by TWINSPAN method.Based on the results of dominant species classification method,the geographical distribution and community characteristics of each association groups and associations was systematically described.5.The 120 plots were divided into three groups by geographical distribution:Loess Plateau,Xilingol plateau and Hulunbeier plateau geographical distribution areas.In terms of species richness,the Loess Plateau is significant higher than the other two distribution areas,there is no significant difference between Xilingol plateau and Hulunbeier plateau.Simpson index and Shannon-Wiener index have no significant difference in the three geographical distribution areas.Pielou index of Hulunbeier plateau is higher than that of Loess Plateau,and there is significant difference.6.On the local scale,the phylogenetic structure(NRI_phy)shows overdispersion,the function character structure(NRI_fun)shows clustering and which is negatively correlated with mean annual temperature.On the regional scale,the phylogenetic structure(NRI_phy)shows clustering,which is negatively correlated with mean annual precipitation.