The tropical seasonal rain forest of Xishuangbanna is one of the typical tropical rain forest of China. The study has been made on the floristic elements of Pometia tomentosa forest community, a very widely distributed and representative type in Xishuangbanna. There are 83 families, 181 genera and 236 species (including 98 tree species) distributed in a 0.25 hac area. The taxonomy, geographic characteristics, ecological components and historical components of the community have been studied and analysed. The results indicate that this community type has a typical characteristics of Southeast Asia tropical rain forest, and the floristic elements reflect the connection and identical characters. The ecological analysis reflects its inclined dry characters , which is caused by the southeast seasonal wind from South Asia. The historical analysis reflects that this community has resulted from very ancient and different forms.

This paper deals with the biomass of the ravine tropicalrain forest at an elevation of 720m(N 22°4/-16/; E 100 ° 32/-44/) in Xishuangbanna. The result showsthat the total biomass is 335.036 t.hm-2 ,of which the tree- layer is 321.185 t.hm-2(95.86%), shrub layer 2.664 t.hm-2(0.80%), herb layer 1.635 t.hm-2/(0.49%), liana 4.078t.hm-2(1.22%), epiphyte 0.092% t.hm-2(0.03% ),litter 5.382 t.hm-2(l1.61%).

By using statistical and analytical methods of the computer data base, this paper deals with statistical data of the floristical elements of the tropical rain forest in Xishuangbanna and mainly the areal-types of families, genera and species, for the purpose to reflect the diversity fea-tures of the floristical elements of the tropical rain forest in this region. The results of this research are as below.

This paper studies the net primary production of ravine tropical rain forest in Xishuangbanna at an elevation of 2300m (N 25 24'E 102 45' ). The estimated NPP(net primary production)of ravine tropical rain forest is 2298.0 g.m-2.a-1, of which 33.32% is stems,18.22% branches,29.56% leaves,14.84%roots,0.39 %flowers,1.26% fruits, and 2.40% leaf biomass grazed by insects.The NPP percentagesoftree-layer.shrub.herb and inter-layer are 88.42% , 3.74%, 4.44%and 3.39% respectively.

In this paper, the phytocoenological method is used to analyse the species structure of the Pometia tomentosa community, a tropical seasonal rain forest community in Xishuangbanna area. The component structure can be devided into five layers, i.e. three tree layers, one tree-shrub layer and one herb layer. There are total 81 tree species with over 2.5 cm in diamter breast high(DBH). The important value index(IVI) of these trees is got through caculation.6 spe-cies of the trees are dominent species by comparing IVI with other species, and Pometia tomentosa is the most dominant species in the community.77 tree-shrub species.21 herbs, 43 lianas and 5 epiphytes are also recorded in the 25 quadrats which are 2x2m (4m2) large in area.

This paper studies the composition of tree population in Pometia tomentosa Communi-ty in Xishuangbanna. The result shows that there are a few adults in tree populations and no dom-inant species in the community. In tree populations.the spatial distribution of individuals is ran-dom and clustered. Most of populations at layer A are random distribution, but at layer C are clustered. The spatial pattern of juveniles and adults might be different. Adults tend to be more uniformly distrubited than expected from the models of their juveniles at layer A populations, but more clustered than juveniles at layer C of tree layer. Number of species and individuals is most at the lower layer, least layer A. Most of populations are continuous population types.

Pometia tomentosa is a canopy species and a characteristic species of the tropical season-al rain forest in Xishuangbanna. With quadrat sampling method for field data, the diameter class structure, height class structure, static life table and survival curve of the trees were set up, and the dynamic rules of the population was analyzed. The result shows that the Pometia tomentosa popu-lation is a continuous increasing population. The mortality rates of seedings is great, suvival rates increased with increasing plant size. There are a lot of seedlings in the population, which are sup-pressed in the understory of the community. The seedlings are of great significance for population recruitment success. The regeneration of the population is related to gaps.

In this paper, the relationship between tree population dynamics and stability in ravine tropical rain forest in Xishuangbanna has been studied. The result shows that the composition of tree populations is unstable and changes with time. The stability of structure and function (photosynthesis production) of the ravine tropical rain forest is maintained by a lot of tree popula-tions, and relative constancy of individuals in each layer. The ravine tropical rain forest has quite resistant to perturbation.

Applying the method of size structure, this paper studies the population dynamics of constructive species of the tropical montane rain forest in Xishuangbanna. In the overstory, size-structure of constructive species Nephelium chryseum is an increasing population which will maintain relative stability over a long period of time. Winchia colophylla papulation has seedlings and saplings, but is short of young trees. Paramichelia baillonii population is short of seedlings and saplings, and is hard to reproduce itself in the dense shade of a forest or tree gap. It appears to be a senescent population. Paramichelia baillonii, Schima wallichii population is short of seedlings and saplings, but it may reproduce itself under tree gaps.

Using the phytosociological method, a preliminary study was made on the Pometia tomentosa forest community. The community is one of the representative types of the tropical sea-sonal rain forest in Xishuangbanna. 25 plots was made in the forest and a synthetic table of the community was got from the study. In the table, the character and function of each plant in the community can be reflected through its abundance-coverage, presence and coefficient of coverage.The horizontal distribution of the species in the community and the classification units under the community can also be obtained from the study.

The various actions of liana in the ravine tropical seasonal rain forest are more abun-dant than that in the tropical moist rain forest, and the young parts of stems possess variable char-acteristics in filling space. The climbing styles of liana can be divided into three types: self-twiner, climbing depending on other species and compound climbing. All of three actions show the secon-dary features in the succession of liana, and they are the results of longterm evolution and adapta-tion among plants and between plant and environment.

Based on the 2 vegetation-types, 9 formations and 16 associations of the tropical rain forest in Xishuangbanna, which have been summarized, revised and renamed by the author, this paper deals with the statistical data of 434 main plant species of 16 association tables of the ecological structure features. A computer data base of all species has been established with the fea-tures of their presence in vegetation types, structure layers, life form types and the ecological morphological features of their leaves. Based on the data base, it has summarized the diversity fea-tures of ecological structures such as the horizontal and altitudinal structures, the spectrums of life form, leaf scale, leaf pattern, leaf texture.leaf margin, leaf apex in the tropical rain forest of Xishuangbanna . These features are similar to those of the typical tropical rain forest of Sutheast Asia, but the tropical rain forest of Xishuangbanna has several north-margin features. As for the features of ecological structures of all plant species, there are more diversity features in this transitional north-margin rain forest than in the typical ones.

Based on the investigation of the tropical rain forest (each one for tropical seasonal rain forest and tropical montane rain forest) in Xishuangbanna, all published and unpublished plant community types from 1980's to nowaday have been summarized, revised and renamed. Then, a regional complete system of vegetation classification has been sorted out:2 vegetation-types(TSRF and TMRF) ,9 formations and 16 plant community types(associations), each community type with a brief association table to show the diversity features of community type of tropical rain forest in Xishuangbanna. The tropical seasonal rain forest (TSRF) is a longitudinal zonational vegetation type in the southern part of Xishuangbanna, in which the hill rain forest is a more typical type. The tropical montane rain forest (TMRF) is an altitudinal zonational vegetation type in the southern part of the Xishuangbanna while it is a longitudinal zonational vegetation type in the northern part of same area, and a non-zonational (azonational) vegetaion type exists also in the southern part of the same area at higher altitude. All of these show the diversity features of zonational vegetaion types in the tropical rain forest of Xishuangbanna.