| Under the backgrounds and developing trends of ecology, forestry and forest of national urban environmental construction, this article combined particular terrain and layout planning of road system in main urban areas of Chongqing, and regarded natural vegetation, semi-natural vegetation and man-made vegetation in either sides of main road in main urban areas as study subject. Then, this research choosed the typical transect of community, investigated the existing status, furthermore, studied and analyzed the main community types, composition characteristics and changes of community species, the minimum sampling area and width of community survey of forest belt, as well as the environmental effects of forest belt in different kinds of forest belt. Moreover, this article discussed the visual landscape structure of different kinds of viatic forest-belt construction in connection with the characters of main urban areas in Chongqing, to provide scientific theoretical foundation for the similar forest-belt construction in Chongqing.The results were as follows:1. According to the difference of constructral function of viatic forest belts in Chongqing main urban areas, the forest belt were divided into 3 types such as belt of ecological protection, belt of leisure and recreation and belt of landscape appreciation. Furthermore, according to the succession order and disturbed degree of forest belt communities, the forest belt could be divided into such 3 main types as natural forest belt, semi-natural forest belt and man-made forest belt.2. Community types and species composition characteristics of different viatic forest belts. In natural belt, the tree layer was mainly constituted of Moraceae, Lauraceae, Leguminosae and Scrophuluriaceae. Top 5 plant species in the shrub layer were Oleaceae, Rosaceae, Liliaceae, Euphorbiaceae and Araliaceae. While in man-made forest belt, Moraceae, Lauraceae and Euphorbiaceae were the chief plants in the tree layer. In the composition of species, natural forest belt was more than man-made, however, the shurb plant species of man-made belt was richer relatively.On dominant index, the quantity of dominant species in tree layer of man-made forest belt was lower than natural belt, and concentrative degree was lower too. Although natural belt had artificial disturbance to a certain degree, the concentrative degree of dominant species was relatively higher. The dominant index of tree layer of different man-made forest belts had differences because of different types of forest belt. For example, compared with other forest belts, the dominant index of belt of leisure and recreation decreased significantly. On diversity index, the species of forest belt communities in Chongqing main urban areas were rich relatively, especially the natural forest belt. The tree layer species of man-made viatic belt was low in diversity, but high in quantity, and the dominant species of it were not obvious usually.3. The minimum area of viatic forest-belt communities in Chongqing main urban areas were calculated according to the species-area curve equation. The results showed that when 60% species of forest belt were included, the average critical area of tree, shrub and herb plant species as well as all the plant species in communities were 118.5 m~2, 97 m~2, 79 m~2 and 82m~2 respectively, and the minimum area of sampling area was about 99 m~2 after analysis. When 80% were included, the average critical area of these were 362 m~2,232 m~2,154 m~2 and 315m~2,and the minimum sampling area was 266m~2 after ananlysis. When 90% were included, the average critical area of these were 641 m~2, 604 m~2,391 m~2 and 571m~2.After analysis, the minimum sampling area was 552m~2.4. The viatic-forest-belt width in survey regions of Chongqing main urban areas were determined preliminarily by analyzing variation of species diversity of viatic forest-belt communities that was on the vertical direction of road. The study showed that edge effect of forest belts in Chongqing main urban areas was between 22.5 m and 27.5 m, so this study suggested that the width of viatic forest belt should be more than 50 m. And according to the analysis of improved degree that viatic belts were to microclimate, the width of viatic belt should bo more than 51.2 m.5. Viatic forest belt had the obvious effect of cooling and humidification,and there were differences of cooling and humidification in different forest belts. In terms of the influence of community canopy density of different forest belts on exertion of community ecological effects, big planting density of man-made forest belt had the remarkable relationship with the effect of cooling and humidification of community, and community canopy density of 3 types' belts had the similar relationship with the effect of cooling and humidification. That was, the greater canopy density, the better the effect of cooling and humidification.
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