| The urban green belt ecosystem plays an important role in maintaining the urban ecosystem balance, and protecting the urban environment. Urban forest ecosystem is the major compartment of the urban greenbelt system, and the main contributor improving urban ecological environment. Therefore, forest ecosystem is the core policy in environment construction project carried out in processes of urbanization and sustainable development in the Pearl Delta region.To evaluate the environmental and ecological benefits of the "green hill green ground and urban forest belt" project in Guangzhou, the forest belt structure and ecological function of urban forest ecosystem in Guangzhou was studied using experimental and monitoring approaches. The result in this study is helpful for providing theory and scientific proof for the "ecological Guangzhou" project. It is also helpful for providing new basis for urban forestry ecological development in national wide.1. Landscape diversity index of the "green hill green ground - urban forest belt and region" was 2.3889, and the evenness index was 0.7619, the path forest belt and region had increased, patches were rich and evenly distributed, but the difference among patches was obvious. With the succession of urban forest belt to natural forest, the secondary broad-leaf forest patch should be introduced. the forest mottling community composing structure should be improved, at the same time, the floristic component increased, the forest community's multiple indices of forest belt region advanced, and the community was increasingly stable, the ecosystem structure and the function were more perfect, the environmental ecological benefit was more remarkable.2. Comparison study in eight 0.2 hm2 forest plots in 13 road forest belts in Guangzhou showed that:mean carbon sequestration in 6a forest belts was 39.5T·hm-2, which were 8.6 and 7.9 times of that in 3a and 4a forest belts, respectively. The 6 a forest belts sequestrated 26.3 T·hm-2a-1 CO2 from the atmosphere and released 19.2T·hm-2 a-1 oxygen to the atmosphere, respectively, which were 4.3 and 5.3 times of those in the 3a and 4a forest belts, respectively. The result therefore highlighted the environmental ecological benefit of carbon fixation and oxygen release of urban forest belt. The biological nitrogen fixation in 6a forest belts ranged from 285.8 to 371.5 T·hm-2, with the mean nitrogen fixation of 328.7 T·hm-2, which was 11.8-14.6 times of those in 3-4a forest belts. The biological sulfur fixation in 6a forest belts varied between 73.6 to 75.9 T·hm-2 with mean value of 74.8 T·hm-2, which was 11.7-15.2 times of those in 3-4a forest belts. For the measurement of forest biological attracting quantity, On average, the 6 a forest belt can absorb 163.2 and 19.3kg·hm-2·a-1 of NO2 and SO2 respectively from the atmosphere, and 3-4a forest belts can absorb 30.5 kg·hm-2·a-1NO2 and 3.7kg·hm-2·a-1 SO2 from the atmosphere, respectively. It can be seen that the 6a forest belt has remarkable ability on alleviating atmospheric greenhouse gases and carbon hydrate compounds. It is also indicated such ability will getting prominent with forest succession.3. Comparison study of biological fixation of heavy metal elements ability in different forest belts indicated that the highest heavy metal element fixation ability was found in forest belt along airport road with the amount of 463.5 g·hm-2Cu,221.1 g·hm-2 Pb,3.3 g·hm-2 Cd, and 2.3 g·hm-2Hg, respectively. The annul fixation ability of heavy metal elements Pb, Cu in 6a forest belt was 36.5 g·hm-2,71.1 g·hm-2, respectively, and that was 4.9g·hm-2 of Pb and 18.4 g·hm-2 of Cu in 3a forest belt. It is obvious that forest belt in this study has significant ability on heavy metal pollutant fixation. The content of heavy metal elements was high in leaf organ of trees in forest belts. Leaves are the organs with sensitive functions, so leaves'absorption mechanism was very apparent.4. Monitoring of tree organ chemistry in 26 species in forest belts showed that the highest organic C content was found in stem, which was higher than that in leaf and branch. Contents of other 6 chemical elements followed the trend of leaf> branch>stem. Contents of S, Pb, and Cu in leaf were remarkably higher than those in the stem, S, Pb, Cu contents in leaf was 4.9,3.3, and 1.8 times than those in stem, respectively, which was on the contrary to the rule of biomass accumulating (stem>branch>leaf). The contents of N, S, Cu, Pb, Cd, Hg in leaf was higher than in branch and stem, indicating leaf has remarkable ability in absorbing metal elements compared with branch and stem.5. The 6a forest belt with 20m in width reduces 35.5% of atmospheric SO2 and 33.8% of NO2, respectively, which was 2.96 and 16.9 times of that in the 3a forest belt. The differences of climate adjustment ability of the two forest belts including:3-4a forest belt with 20m in width reduced 0.6℃in air temperature, and increased 1.7% of air humidity, while 6a belt with the same width reduced 2℃in air temperature, and increased 2% of air humidity. The ability of decrease air temperature and increase humidity of 6a forest belt were 3.3 and 1.2 times to the 3-4a forest belt, respectively. and reduced wind speed 50%.6. Environmental ecological effects of different forest belts varied greatly with belt with:the 20-m forest belt absorb 7.6%,3.3%, and 9.9% of SO2,NO2,and NO, respectively more than those by the 10-m forest belt. Continuous forest belt is effective in reducing pollution gas density. The 20m width forest belt community reduces 20.0% of SO2 and 27.6% of NO2 compared with the non-forest belt.7. The temporal and spatial characteristics of pollutant gas reducing ability in forest belts with different width varied with weather condition:in the cloudless days, the 10m forest belt reduced from 50% to15% of SO2 gradually from 10:00 to 14:00, then gradually increased to about 45% at 18:00. While in cloudy days, the 10m forest belt reduced 20% of SO2 from 9:00, and gradually increased to 55% at 18:00; In the cloudless days, the forest reduction rate from 10m to 20m forest belt increased gradually from 45% to 55% at various time intervals. While for forest belts with 20m to 30m in width, the reduction rate decreased gradually from 20% to 46% at various time intervals. The highest SO2 reduction rate was observed in the 20m forest belt at 10:00 and 18:00. But in the rainy days, the SO2 reduction rate for forest belt with width increased from 10m to 30m with time, and the reduction rate was inclines increase, varied from 25% to 70%. And the highest reduction rate was found in 30m forest belt from 15:00 to 18:00. So the temporal and spatial characteristics for reducing SO2 of the two types of weather conditions were apparently.8. The spatial and temporal characteristics of different forest belt width effect on NO2 reduction in different climate condition reflected:in cloudless days, the 10m forest belt reduced NO2 to the highest at 10:00-12:00, which was more than 55%. Forest belt with 30m in width the amount of reduced NO2 increased to the maximum value of 85.6% at 12:00-14:00. and the increase gradient was higher than that in the 10m and the 20m forest belts. In cloudy days, N2O reduction rate in 10-30m width forest belt increased from 32% to 82% from 9:00 to 12:00. The NO2 reduction rate of the whole forest belt increased gradually above to 85% at 12:00-17:00 interval, then it decreased to 75% at 18:00. Therefore, in both cloudless and cloudy days, the highest NO2 reduction rate occurred at 12:00-17:00.9. In the cloudless days, the 10m forest belt along road decreased air temperature gradually from 0.6℃to 1.3℃from 9:00 to 14:00, then fell to 0.8℃from 14:00 to 18:00. The temperature reduction in the 20m forest belt, increased from 1.1℃to 2.1℃from 9:00 to 14:00, then fell to 0.8℃at 18:00. The temperature reduction in the 30m forest belt increased from 0.1℃to 2.5℃from 9:00 to 14:00, then fell to 1.0℃at 18:00. It was the watershed of temperature reduction at 14:00, and the lowest temperature was observed at 30m forest belt. From 9:00 to 11:00, the temperature reduction increased with the width increased from 10m to 20m, and decreased from 20m to 30m; From 14:00 to 18:00, temperature reduction increased in 10m-30m forest belts. In cloudy days, temperature reduction increased with the increase of forest belt width from 10m to 30m at 9:00 to 15:00, the temperature deduction was 0.7℃at 9:00, it increased to 1.0℃at 15:00, then decreased to 0.1℃. The temperature reduction decreased with the time in the 0m-30m width forest belt from 15:00 to 18:00.10. Soil organic carbon stock in the 6a forest was 91T·hm-2, which was 1.8 times than that of the 3a forest. It was apparent for the the forest belts in decreasing heavy metal elements.11. The contents of heavy metal elements, including As, Cu, and Zn, in the soil was significantlynegatively correlated with Catalase. They were negatively correlated with Urease and the acid phosphatase, while positively correlated with Protecses, but the correlation between heavy metal elements and Protecses was not statistically significant. Excessive heavy metal elements in the soil strongly suppressed the activeness of soil Catalase, indicating that soil Catalase can sensitively reflect soil heavy metal pollution condition. Therefore, the activity of Catalase can present As, Cu and Zn pollution conditions in forest soils.12. Forest belts had various functions of alleviating noise. The relationship between forest belts and noise weakening ability can simulated by the equation y=axb. Among the 5 different forest belts, the forest belt with entire arbor - scrub - grass structure was more efficient in alleviating noise than the belt has only arbor layer. The maximum difference between these two belts in noise reduction is 12.5dB.
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