Distribution pattern of plant sexual system diversity in Populus lasiocarpa Oliv. community.

The diversity of plant species and sexual system in a Populus lasiocarpa Oliv. community in the Dalaoling Nature Reserve of Hubei Province were assessed by richness index, diversity index and evenness index. In total, 182 species representing 143 genera in 73 families are recorded in P. lasiocarpa community. The genera with only one or two species occupy the dominant position in community. The species richness in P. lasiocarpa community is affected by the elevation, slope and the forest microenvironment. It reaches the maximum value at the quadrat 3. The more common families and less common species among the four quadrats are related to the degrees of difference among their microenvironments. The P. lasiocarpa community is in the process of succession. The age structure of P. lasiocarpa belongs to an increasing type in the quadrat 1, but a declining type for the other three quadrats. The sexual system of plants is diverse in P. lasiocarpa community. Hermaphroditism has the highest proportion and monoecious and dioecious plants also play the important role in the community. In the tree layer, the most important type is dioecy, which is consistent with the sexual system of the constructive species. The hermaphroditism is the most important type in the shrub and herb layers and the proportion of hermaphroditism increases with the increasing number of species in the herb layer. In addition, the importance values of the constructive species, P. lasiocarpa, is the maximum in the tree layer, especially in the quadrat 3. The changes of species diversity index are consistent with sexual system diversity index in the four quadrats. The diversity index of the tree layer change little, but it increased gradually with the increasing elevation in the shrub layer and reached the maximum at the quadrat 3 in the herb layer, which is affected by the number of species in different layers. The evenness index is the maximum in the lowest elevation in all three layers, indicating that the most even distribution of plant species and sexual system.