Patterns of tree species composition of secondary natural vegetation along an altitudinal gradient on earthy-rocky mountainous area in western Shanxi Province

The patterns of dominant species and ligneous plant community diversity was analyzed at different altitudinal gradients in the earth-rocky mountainous area in western Shanxi Province.The result are as follows: the dominant species had regular change in different altitudinal gradients;the species richness of all the ligneous plants decreased with the increment of altitude.The tree species richness was high in the community of high altitude,but the shrub species richness was high in the community of low altitude.In most altitude the richness of shrub species was greater than that of arbor species.The α diversity of arbor layers was big in high altitude,however the α diversity of shrub layer decreased with the increment of altitude.In the β diversity research,the Cody index and Whittaker index were studied in the communities of this region.The result indicated that the β diversity index was low among the communities of neighboring altitude,but the index increased when the distance was high between the communities.The result showed the value of β diversity indices was maximal in the region of about 1 650 m altitude.