Study On Population Ecology Of Thuja Sutchuenensis--A Rare And Endangered Endemic Plant Of China

This paper focuses on Thuja sutchuenensis, a rare and endangered endemic plant of China. The bio-ecological characters, species diversity of its communities, population size-classes structure, distributional pattern and genetic diversity of populations were studied, which are the scientific basis for the efficient conservation of Thuja sutchuenensis. The main results are as follows:The bio-ecological characters of Thuja sutchuenensis are photophilic, oligotrophy tolerant and slow growing. The types of soil where the species exists are usually the brown ones which pH value is close to be neutral or slight slkalis.Thuja sutchuenensis is dominant species or one of codominant species in the communities. Generally, the species richness order, in all communites is that the shrub layer﹥herb layer﹥tree layer, the diversity index order is the same as above. But the evenness order is that tree layer﹥shrub layer﹥herb layer. At the level of community, both of the species richness and diversity index in T.sutchuenensis- B. sinica community (Ⅳ) are the highest one and species evenness in A. caudatum var. multiserratum- T.sutchuenensis community (Ⅰ) is too. As for eco-dominance, the order is tree layer﹥herb layer﹥shrub layer and that of T.sutchuenensis- B. sinica community (Ⅳ) is the lowest one among four community types. Richness index R2 is very sensitive to the number of individuals, so it is suggested to use prudently.The types of population size structure which is of serious imcompletion are classified into the growing type, the initial declining type, the mid-declining type and declining one. Combining with the high death rate of seedling and sapling, shown in the field surveying, T.sutchuenensis populations are thought as senescent populations.Population pattern of T.sutchuenensis turns out to be manifestly contagious distribution. At the small sampling scale (communityⅠ, Ⅲ, Ⅳ is 4m2；Ⅱ6m2 ), the contagiousdegree is the highest than other scales.And with the extention of the sampling scale,the degree of contagition get fewer and fewer.As regard contagious degree of four different communities, the order is A. caudatum var. multiserratum- T.sutchuenensis community(Ⅰ)﹥T.sutchuenensis-T.chinensis community (Ⅱ)﹥T.sutchuenensis-Q.engleriana community (Ⅲ)﹥T.sutchuenensis-B.sinica community (Ⅳ).Compared with other species of Pinale, percentage of polymorphic loci (77.27%), Shannon genetic diversity index (0.3992) and Nei's gene diversity (0.2668) of T.sutchuenensis show that the species'genetic diverstiy lies at higher level.Genetic variation within populations cover most variation within species(Hpop/Hsp＝0.647),but variation among population occupy relatively fewer((Hsp-Hpop)/Hsp＝0.353,Gst=0.3368).Gene flow among populations is very low (Nm =0.4932),so genetic shift become the main factor to make up genetic variation among populations.The relationship between genetic distance and spatial distance is insignificent.In summary, although the genetic diversity level of Thuja sutchuenensis is at high level, many factors, such as human disturbtions, lower level of gene flow, high death rate of seedling and sapling etc, have made it very difficult to regenerate naturally. Measures to be taken to conserve the species effectively are very necessary.