This paper is a part of studies of the mangrove forests in Dongzhai harbour of Hainan island, China. It deals mainly with the accumulation and biological cycle of K and Na elements of 55-year-old Bruguiera sexangula community.

The main results of the measurements are as follows:

1. The amounts of K and Na elements in standing crop of this community were 669.9kg/ha and 2591.3kg/ha in which the amounts of two elements in aerial part of biomass were 425.6 for K and 908.9 for Na (kg/ha), and that of below ground biomass were 244.3 for K and 2042.4 for Na(kg/ha) respectively.

2. In biological cycle of K and Na of this stand, the annual value of vegetation mineral uptake were 89.6 for K and 204.4 for Na(kg/ha), of its return were 49.0 for K and 99.8 for Na(kg/ha) and of its retention were 40.6 for K and 104.6 for Na(kg/ha), respectively.

3. The turnover period of K (14 yrs.) is faster than that of Na (30 yrs .)

This paper deals with the biomass and production of roots,stems,foliages and branches of Tapiscia sinensis in the seedling and its forest. We have investigated the allocation of the biomass and energy in T. sinensis forest. The biomass dynamics of grass is determined by periodical harvest method, the model tree method to the biomass of forest and the CA-3 type calorimeter to the plants caloric values.

(1)The biomass of one-year old seedling sheltered from the sun with traditional is 1777.5g/ha. The biomass of seedlings sheltered by one layer of plastic sheeting from the sun is heaviest, that in full time illumination is second and that sheltered by three layers of plastic sheeting is lightest.

(2)The biomass of the above-ground part of naturally regenerated T. sinensis individual of 16 years old is 107.77kg.

(3)The total biomass of artificial T. sinensis forests of 8 years old and their mean net production of arborous layer are 80.63t/ha and 9.563 t/ha·a respectively. These data show that the biological productivity of T. sinensis is higher than that of Cunninghamia lanceolata in Huitong county, Hunan Province and in southern Jisngsu Province.

(4)The net primary production in T.sinensis forest is 1219.18g/m2·a; among them the arborous layer is 956.25g/m2·a; the grass layer and naturally seedlings are 161.10g/m2·a; the litter layer is 101.83g/m2·a. The utilization rate of solar energy in T. sinensis is 0.527 per cent and that of arborous layer is 0.417 during the growing season.

The wild grass communities extensively distributed in North China is a secondary coenotype into which the primeval vegetation was turned by artificial destroy. Now, papers studying wild grass communities by the quantitative method are rare. This paper made a cluster analysis of the wild grass communities on Mount Tai by a group-average method. At the level d=2100, we can distingush 12 coenotypes. The results also show that;

1. It is practical to completely classify the wild grass communities by the numerical method.

2. The major coenotypes are coincident with the traditional classification, in which there are eight communities defined as association types.