| Content:The content of this paper was on the study of the north slope of Mt. Laotudingzi in the Laotudingzi Natural Reserve,based on the method of field plots investigation,a total of 9 sites were set along the altitude gradient to investigate the types and characters of plant community,the changes of species diversity of herb layer along the altitude gradient.The results obtained as follows:1.The species composition and plant community typesWe recorded 27 tree species,32 shrub species and 102 herb species in 9 plots on the north slope of Mt.Laotudingzi,in which,there were 102 herb species belonging to 81 genera and 34 family.Umbelliferae,Labiatae,Liliaceae,Compositae and Cyperaceae were frequently appeared.According to composition of the life type of herb plants,perennial plant had 98 species covered 96%of the total plant recorded, and therophyte covered 4%which existed 967m below.Because of the peculiar geographical condition,there was a clear vegetation vertical belt on the north slope of Mt.Laotudingzi with the name of communities along the altitude gradient were deciduous broad-leaf forest,mixed and broad-leaved forest community,sub-alpine coniferous forest community,mixed and broad-leaved forest community,alpine birch forest community,shrub and Alpine meadow respectively.2.The changes of herb layer species diversity along the altitude gradient on the north slope of Mt.Laotudingzi①The changes of herb layer species richness along the altitude gradient The changes of herb layer species richness on the north slope of Mt.Laotudingzi along the altitude gradient was complicated that it was high on two sides of the mountain and low in the middle altitude,that means the minimal and maximal values appeared continuously at the altitude of 1067m and 1167m,which named sub-alpine coniferous forest community and mixed and broad-leaved forest community with the species amount of 6 and 38 respectively.②The changes of herb layer a diversity along the altitude gradient The changes of Shannon-Wiener index and Simpson index along the altitude gradient were the same as that of species richness,Shannon-Wiener index fluctuated more greatly than the other.Two indexes were at the range of 1.026-2.655 and 0.607-0.911 andthe maximal value appeared at the altitude of 1367m and 1317m respectively,the minimal value were all appeared in sub-alpine coniferous forest community at 1067m.The pattern of PIE index was also similar to that of species richness,the maximal and minimal values appeared in the same community which Simpson index did with the value of 0.894 and 0.291.The evenness index Jsw and Jsp had the similar fluctuation along the altitude gradient,the maximal value came to 0.955 and 0.980 at the altitude of 767m and 1317m,the minimal value of two indexes all appeared in mixed and broad-leaved forest community with the value of 0.889 and 0.904.③The changes of herb layerβdiversity along the altitude gradient The maximal value of Whittacker index is 37.44 at the sub-alpine coniferous forest community where the species richness was the lowest along the altitude gradient;the minimal value appeared at 1317m,the mountaintop.The peak values of Cody index appeared at the 767～867m and 1167～1267m which showed the transition zones from deciduous broad-leaf forest to mixed and broad-leaved forest community and from mixed and broad-leaved forest community to alpine birch forest community respectively.Bray-Curtis index and Morisita-Horn index which belonged to the types of quantitative property had the same function which the Jaccard index and Sorenson index had to indicate the similarity of communities.The first peak value of the four indexes were appeared in the mixed and broad-leaved forest community at 867～967m,and the second peak value appeared at 1267～1317m except that Morisita-Horn index was at 1167～1267m.The changes of two property index had indicated the difference of species composition in different communities on the north slope of Mt.Laotudingzi directly.
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