Altitudinal Distribution Pattern of Seed Plant Diversity in Shangrila County

The database of plant species was built based on the systematic survey of three provincial level nature reserves in Shangrila County, and the altitudinal distribution pattern of seed plant species in the county was studied by means of establishing the DEM digital elevation model integrated with the elevation distribution feature of the plant species. The results showed that there were 3 794 species belonging to 876 genera and 163 families of wild seed plants in Shangrila County. The richness and density of the species, genera and families all showed the singlepeak curve along with the elevation increment. There were principal consistences between the change in richness and density of the species, genera and families with the altitude variation. The maximum values of species density, the richness of genera and families appeared at lower altitude around 1 900-2 200 m range, whereas the maximum value of species richness appeared at mid altitude range of 3 100-3 400 m. The formation of vertical distribution pattern of species richness was related to water and heat conditions, and the boundaries of species distribution that were all reflected by the altitude, and also affected by the “middle expansion effect”. As seed plants are the composition of MidNorth Temperate Zone, and the major floristic type of Shangrila County, the proportion of north temperate elements was increased with the increment of altitude, whereas the proportion of tropical elements was decreased. There was a floristic balance point around 1 750 m in elevation.