Pure coniferous forests planted repeatedly on the same area have many defects. Planting mixed coniferous broad-leaved forests is one of the most available methods to dispel these defects. Significant effects have been seen from experiments done in the past seven years. It was found that the mixed forest of Cunninghamia lanceolata-Michelia macclurei with rational proportion of arrangement has shown significant economical and ecological benefits.The advantages of mixed forest are as follows:increasing biological productivity and utilization of solar energy,accelerating the decomposition process of organic matters and accumulation of nutrients and humus on the woodland,improving the mechanical composition,aeration condition and capacity of water retaining and supply of the soil, promoting the activities of microbes, and decreasing insect pests.

The characteristics of percolation of different vegetation-soil types and land uses were studied at Jianfengling in Hainan Island, China. Seepage water was collected by a number of open dish collectors from different layers of soil. The relationship between rainfall and seepage water in the area, and characteristics of substance movement in tropical forest ecosystem were analysed. According to two-year observation, it was shown that the annual percolation within 100cm depth of the lateritic yellow soil under the mountain rain forest was 355 mm, equal to 15.9% of the annual rainfall, while in the cinnamon latosol under the semideciduous monsoon forest it had only 30mm which was 1.8% of the annual rainfall. The litter cover and the upper 30cm of surface soil hold the maximum seepage water. The forest has an excellent function of soil and water conservation. The seepage capacity is positively correlated with rainfall, but the deeper the soil, the less the significant correlation is.

Aneurolepidium chinense steppe and Stipa grandis steppe are two main community-types of the typical temperate semi-arid steppe in eastern part of the Eurasian continent al steppe region, widely distributed in the eastern part of the Mongolian plateau. Their structures are closely related to grazing pressure. This relationship was analysed based on two typical gradients of grazing pressure. The fuzzy cluster expressed the divergence of the similar communities under different grazing pressure and the convergence of the different communities under heavy grazing pressure, i.e., both Aneurolepidium chinense steppe and Stipa grandis steppe will change into Artemisia frigida steppe through the regressive succession if sustained grazing pressure is imposed.

This thesis is a preliminary study of the litter in Aneurolepidium chinense meadow. The dynam cs of the litter’s decomposition, accumulation and nutrient contents are examined.Based on the collected data, the simulation models for decomposition and accumulation of the litter have been built by computer analysis.Disappearance rate is 0.4065g/g·a. The seasonal change of the rate of lost weight is in accord with the Logistic curve. The decomposition activity is very strong from May to September. The lost weight of litter during this period makes up 90 per cent of the annual lost weight. Decomposition action nearly ceases in winter. Under the present condition of Aneurolepidium chinense meadow, it will take about 7—8 years to approach a steady accumulation quantity of 95 per cent. The maximum accumulation quantity is about 572g/m2.The contents of chemical composition continuouly declined in comparison with the early stage of the decomposition process. The loss of N, P and K is relatively faster than that of the other elements. Cellulose decomposes more slowly. The order of loss of every chemical composition is K>P>N>Na>Ca>Mg> Fe>cellulose.

Flatstalk Bulrush is a perennial, notorious weed which spreads over the paddy-rice fields and lowlands in the world. It has a distinct growth rhythm. Its sexual reproduction is more limited than vegetative propagation in relation to the growing season. Under the semi-sunshine condition, it cannot produce seeds, and its vegetative propogation is retarded.The stage of development of Flatstalk Bulrush is correlated to leaf age. The equation of linear regression of its regrowths can thus be predicted by the leaf age of main stalks as: Ŷa= –36.74+6.24x (1983), and Ŷa= –32.42+6.28x (1984) ; The equation of linear regression for predicting its tuber is. Ŷt= –67.97+l0.12x (1983) , and Ŷt= –33.91+ 8.04x (1984). The weed control with machine and man-power can suppress forming tuber and producing seeds but help its regrowths spread out.The occurrence and distribution of Flatstalk-Bulrush are correlated with cropping system. The emergence of its seedling is later and concentrated than its regrowths which are the main object to control. The farm practices show that the better way to kill the weed is an integrated control, i. e. the combination of agricultural, biological chemical and other methods as well.

The present paper is a study of the SO2 elimination capacity of some plants in Taiyuan to assess the biological elimination parameters in the environmental atmospheric capacity in the city. The study includes three parts. 1) Investigation on the annual biomass of plants; 2) Determination of the SO2 absorptive intensity of plants and the period of SO2 absorption-transformation-transportation by their leaves by means of simulated fumigation; 3) Assessment of the total SO2 elimination capacity of the plants in this area.In Taiyuan, the biomass of tree leaves is 180,000 tons per year and their average SO2 absorptive intensity is 1.89%. The period of SO2 absorption-transformation-transportation of the leaves is about 30 days, and the activity duration of the leaves is 90 days, three times as long as the period.. Therefore, all the trees in Taiyuan can absorb about 10,000 tons of SO2 every year.In the suburbs of this city, the crop biomass is 250,000 tons per year. The absorptive intensity is 0.45%, The period of SO2 absorption-transformation-transportation is 20 days. The activity duration of crop is about 40 days, two times the period. So the crops in the suburbs could absorb about 2,000 tons of SO2 per year.The total amount of SO2 absorbed by both trees and crops, about 12,000 tons,is regarded as the total SO2 eliminating capacity of the plants over the area every year. Within the investigated range of 525 square kilometers, the maximum average potential SO2 eliminating capacity of the plants is 24.0 tons/sq.km/year.The results suggested that the elimination of SO2 from the air with, plants is an economic, convenient and effective way, in addition to treatment of pollution sourses and control of pollutant discharge.

The authors investigate the ecogeographical distribution of Toona Ciliata var. pubescens and analyse its growing regularities, climatic and soil adaptabilities, utilization ratio of sunlight energy and nutrient absorption, accumulation, and cycling characteristics of the young trees introduced in Nanjing.