| Because of the abominable environments, such as serious soil and water loss, limestone mountain region has long been considered unsuitable for trees. However, a natural secondary forest including dominant Ulmaceae species like U.gaussenii, U.chenmouii, P.tatarinowii, Z.schneideriana has taken shape on the Langya mountain, Anhui province, because long-term strict protection has been carried out here. Among the four speices mentioned before, U.gaussenii and U.chenmouii are rare and endangered, the other two are important north subtropical species, with very unique ecological significance. On the one hand, Ulmaceae species has evolved into the dominant populations of the climax community; on the other hand, strong internal competition among Ulmaceae community occurs all the time. When the environmental factors overload, U.gaussenii often fails in the competition with P.tatarinowii which demands a similar niche, leading to death. So it's urgent to take protective measures according to their different ecological characteristics in order to maintain a steady relationships between species and within species.In order to understand the population structures, distributions, mechanisms of endangerment and other issues of Ulmaceae species on the Langya mountain, we have field research and comparative study on the photosynthesis of the four different speices. We also have a comparative study of individuals of different age. In a word, we set two goals: (a)give a explanation of the supersedure and competition situation of Ulmaceae species; (b)give reasonable proposals for the protection of endangered speices of Ulmaceae species on the Langya mountain. The results showed that: (1) The physiological and growth characteristics of Ulmaceae species (low LCP: 9.219-20.823μmol·m-2·s-1, low Rd:0.367-0.458μmol·m-2·s-1, and high SLA:202.328-332.885 cm2·g-1, etc.) contribute to the evolution into the climax community, however, the survival of Ulmaceae species still face such challenges as the environment degradation and human disturbances.(2) The competitive ability Ulmaceae species differs considerably. P.tatarinowii and Z.schneideriana, which have higher Pn:6.218μmol·m-2·s-1 and 6.547μmol·m-2·s-1, lower LCP: 9.219μmol·m-2·s-1 and 13.934μmol·m-2·s-1 and higher LSP:479.422μmol·m-2·s-1 and 496.156μmol·m-2·s-1, etc., have much stronger photosynthesis than the two endangered speices:U.gaussenii and Uchenmouii; During the process of competition, the two endangered speices always lose the resources gradually and die out at last.(3) Narrow distributions, small populations and isolations will significantly enhance genetic drifts and inbreeding effects, which will lower individual fitness and population viability through inbreeding depressions and Loss of heterozygosity. Also the genetic depression of endemics was significantly higher than the other speices. So it's rather urgent to have comprehensive analysis of the genetic structure of these populations and provide a theoretical support for their conservations.(4) Selective pruning of the canopy, increasing the number and size of gaps, may also be effective in promoting growth and regeneration of inferior species and ground seedling. "Species recovery project" plays an active role in protecting species in the short term, but not necessarily to achieve goals:long-term protection of endangered species, particularly the conservation of endemic species with extremely narrow distributions and special habitats. Species recovery project combined with scientific restorations and strict protection of the habitats may be effective for protection of the endangered endemics and ecosystems.(5) We developed 6 nd 5 SSR primers for U.gaussenii and Uchenmouii respectively, which can be used for further study of genetic characteristics of them.
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