Green-land is a vital component of an urban ecosystem and plays an important role in purifying the environment. Especially in large-scale industrial districts, the ecological services provided by vegetation are beneficial to protecting local environments. In this study, amounts of CO2 absorbed, O2 released, heat absorbed through transpiration, SO2 reduced, dust retention and noise reduction have been selected as main variables of study. These indexes allow qualitative assessment of ecological services based on the leaf area during the field work in the workshop area of the Wuhan Iron and Steel Company. Generally, the identified indexes were calculated from the observed data collected in field survey.
The green-land leaf area was obtained through investigation of synusia (No.2 synusian devised by H.Gams in 1918) structure and covering, leaf area index (LAI). All the indexes were calculated based on the estimated leaf area. This was combined with an assessment of value through brought by the ecosystem. The areas of interest included CO2 absorption with the carbon tax, O2 release with the value of marketed products, heat absorption by transpiration with the substitution of electricity, SO2 absorption and dust retention with the market valuation, noise reduction with the will-paying. The ecological services of green-land in urban industrial areas were estimated by measuring the ecologic benefit per unit. The results showed:
(1) Most trees planted in the workshop area were native species. Of them, the majority were of arbor decent. The leaf area was highest in different synusia. The evergreen and deciduous arbors were 409.0 hm2 and 399.8 hm2, respectively. And the sum of leaf area in different workshop areas was 1694.21 hm2.
(2) The ecological benefits of green-land mainly depend on the amount of green space. The capacity of the ecological service of plant was determined by the physiological characteristic of plant and leaf surface as well as by the structure of tree crown. Since the synusias were composed by various plants with different capacity, their ecological benefits were different. While the SO2 reduction absorbed by evergreen was the highest at 0.81 g•m-2•a-1of all synusias. And the ability of evergreen shrub and deciduous shrub was stronger, while that of the herbaceous plant was the weakest.
(3) In 2001, the total green-land area was 312.38 hm2 in the workshop area of the Wuhan Iron and Steel Company. The amount of CO2 absorbed, O2 released and dust retention reduced by green-land in the workshop area were 23850.50 t•a-1, 17345.82 t•a-1 and 2884.51 t•a-1, respectively. The total value of ecological benefits was 201,002,100 Yuan. Among them, the value of heat absorption was the highest at 163,305,600 Yuan, followed next by that of CO2 absorption at 29,693,900 Yuan. The amount of SO2 reduction was lowest at about 3,900 Yuan. In addition, the value of O2 released, dust retention and noise reduction were 6,938,300, 490,400 and 570,000 Yuan respectively.
In summary, the plants with better adaptation and ecological effect should be strategically chosen and combined in different ways for their diverse benefits in varying ecological environments. The leaf area also could increase by combining the arbor, shrub and herb to realize the maximum ecological benefits, giving greater ecological service for improved environments in industrial districts.