Study On Community Characteristics And Population Dynamics Of Rare And Endangered Plant Davidia Involucate Baill.

Davidia involucrata Baill which also called Shuilizi or Dovetree is famous as an ornamental plant in the world. It belonging to Davidiaceae with a single genus to China,is a relic species of paleotropical kingdom in tertiary period, it mainly distributed in Sichuan, Yunnan, Guizhou, Gansu, Shaanxi, Hunan and Hubei.The nature of the community is typical of mixed ever green deciduous broad leaf forests in mountain region of mid subtropics. In recent years,the increasing intensity of human activities and the increase of regional developing items led to a sharp decrease of natural distributed area and natural population number of rare and endangered species Davidia involucrate,and now. its natural distributed populationis on the point of extinction. This species has been listed as Chinese national first protective plant.This paper analyzed the community structure, natural regeneration and plant diversity characteristics of Davidia involucrata, The preliminary conclusions reached in this study are a result of field research in the Hupingshan Nature Reserve and the Badagongshan Nature Reserve by using the sample plot method and enquiry with inquiry:(1) The habitat and area-types of Davidia involucrate community. The suitable distributive area of the community is of warm and moist habitat with abundant rainfall,frequent cloud and few sun light,The land form is precipitous with deep cut valleys. The species of the community are very rich. There are 106-160 vascular plant species in the community belonging to55-73 families and 94-132 genera.The composition of Davidia involucrata community was that the East Asia Plants was the largest,Next was North Temperate Zone. Overall, the Temperate element component in the flora of the community of Davidia involucrate is larger than in the Torrid element, which was similar to that in Yunnan,Sichuan,Gansu.The component of species have the typical transition characteristics that from the subtropics to the temperate zone. In addition, the Cretaceous Period and Tertiary period floristic compositions in the Davidia involucrate community,That Davidia involucrate community with the nature of remnant plant communities.(2)The structure and life form spectrum of Davidia involucrate community.The community vertical structure was simple, which composed of tree layer, shrub layer, herb layer and interlayer plant. The Community composition based on the deciduous trees, which is larger than evergreen trees.the shrub layer coverage at 15% and herb layer is generally between 70%-80%.Davidia involucrata is generally difficult to form the dominant species in the forest community,Only in some local areas which is special habitat conditions, It formed a predominante community by Davidia involucrata. Herb layer was better than tree layer and shrub layer. By comparing Badagongshan, Wenxian,Wolong, Seven-sister, according to Raunkiaer's classification system of life form,the phanerophytes are the top in the community, Followed by the hemicryptophytes,the chamaephytes, the therophytes, the geophytes.(3) The species diversity of Davidia involucrate community.The Simpson diversity indices in herb layer (0.88-0.94) were higher than that in tree layer (0.79-0.93) and shrub layer (0.72-0.91). The Shannon-wiener diversity indices in herb layer (2.72-3.19) were higher than that in tree layer (1.93-2.88) and shrub layer (1.92-3.11).The Pielou indexs Jsw in tree layer (0.85-0.93) were higher than herb layer (0.65-0.87) and shrub layer (0.77-0.89). The community of Badagongshan and Hupingshan are rich in biodiversity.Davidia community diversity at different altitudes show that herbs species and numbers is decreased from low altitude to high altitude, In contrast,The purpose of the shrub layer is increased. By comparing Shannon-wiener diversity index and Evenness index in above 1500m sea level of Hupingshan, Seven-sister, Wolong, all levels of biological diversity for the herb layer> shrub layer> tree Layer.But the Shannon-Wiener diversity index is higher in shrub layer of the Seven Sisters Mountains in Hubei Davidia involucrata community, Evenness index is lower in the shrub layer,because of the shrub layer is dominated by one or two species.in general, the plant diversity of Davidia involucrata community is rich.(4)The population dynamics characteristics of Davidia involucrate. According to establish the Davidia involucrate size and height class structures, produce a time-specific life table in Badagongshan and Hupingshan; and survivorship curves were drawn. The results showed that the population structure of the Davidia involucrata population was a inverse-pyramid type. The death rate of young tree is high,it can be seen Davidia involucrata population was declined in Hunan province.and the survival curve has the trend to be the type between DeeveyⅡandⅢ, From early age to old age, the population was first characterized as unstable,then stable. The results is similar to Sichuan,Guizhou,Gansu area.The survey found young seedlings is so scarce in sampling plot.Natural regeneration ability of Davidia involucrata was weak and seed germination was low,which a little Seedlings and rely mainly on sprout regeneration.