Evaluation On The Ecosystem Services Of Urban Green-land In Industrial Areas

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, noise reduction and health care have been selected as main variables of study. These indexes allow quanlitative assessment of ecological services based on the leaf area and GIS during the field work in Wugang industrial districts. Generally, the identified indexes were calculated from the observed data collected in field survey. The vegetation quantity of leaf area was obtained through investigation of synusia (No.2 synusia 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 industrial districts of interest includ CO₂ absorption with the carbon tax method, O₂ release with the shadow price method, heat absorption by transpiration in summer with the substitution of electricity, SO₂ absorption and dust retention with the market valuation method, noise reduction and health care with the result reference. The ecological value of different region and different structure type of green-land in urban industrial areas were estimated by measuring the ecologic benefit per unit. The results showed:(1) The LAI of synusia is different and it is determined by the LAI of ornamental plants which composed the synusia, and the LAI of urban ornamental plant depends not merely on the single leaf area, also on the shape of tree crown and the intensive degree of branches and leaves. According to the LAI size of different synusia, the sequence was as follows: hedge(13.62)＞evergreen shrub(ll.4)＞deciduous broad-leaved arbor (10.75)＞evergreen broad-leaved arbor (10.07)＞herb (7.61)＞coniferous arbor (6.61)＞deciduous shrub (5.78).(2) The leaf area vegetation quantity of green-land is determined by the area of green-land and the LAI of main ornament plants and the leaf area vegetation quantity of Wugang industrial districts was 12588.23 hm². Of them, the majority was of arbor decent. and the leaf area vegetation quantity was the highest in different synusia. The evergreen and deciduous arbors were 2834.12 hm² and 4263.49 hm², which occupied 22.51% and 33.87% of leaf area vegetation quantity, respectively. The green-land are dominated by arbor＋shrub and arbor＋shrub＋herb that occupies 34.65% and 33.40%of green-land area and33.48%, 33.43% of leaf area, respectively.(4) The ecological benefits of green-land mainly depended on the amount of green space. The capacity of the ecological service of plant was determined by the environment factor, 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. The transpiration rate of herb was highest in summer at 2.33 mmol. m^-2. s^-1 in all synusia. The transpiration rate of evergreen broad-leaved arbor and evergreen shrub was small, which was 1.07 mmol. m^-2. s^-1 and 1.16 mmol.m^-2. s^-1, respectively.The ability of SO2 reduction absorbed by evergreen broad-leaved arbor was the highest in all synusias at 1.6104 g.m^-2.a^-1, while that of deciduous shrub was the lowest at 0.2152 g.m^-2.a^-1. And the ability of dust retention of evergreen shrub and deciduous shrub was stronger, which was 0.8026 g.m^-2.d^-1 and 0.8568 g.m^-2.d^-1, respectively, while that of the herbaceous plant was the weakest at 0.2501 g.m^-2.d^-1.(4) In 2004, the amount of CO2 absorbed, O₂ released, SO₂ absorption and dust retention reduced by green-land in Wugang industrial districts were 168.07x103 t.a^-1, 120.65x103 t.a^-1, 106.78 t.a^-1, 2884.51 t.a^-1 and 25234.21 t.a^-1, respectively. And the amount of those per unit area were 14.085 kg-m^-2.a^-1, 10.111 kg·m^-2·a^-1, 8.950 g·m^-2·a^-1 and 2.115 kg·m^-2·a^-1, respectively. While the amount of heat absorption by transpiration in summer was 25.63x109 kJ·a^-1 and that of per unit area was 2147.951 kJ·m^-2·a^-1.(5) In 2004, the total value of ecological benefits of green-land in Wugang industrial districts was 273, 386, 000 Yuan. Among them, the value of CO₂ absorbed was the highest at 209, 240, 900 Yuan and the value of SO₂ reduction was the lowest at about 64, 100 Yuan. The difference of ecological vale of per unit green-land area among different regions is small, and it was between 22.310 yuan·m^-2·a^-1～23.290 yuan·m^-2·a^-1. Among the 7 structural types green land, the ecological value of per unit area of the shrub＋herb, the arbor＋shrub and the arbor＋shrub＋herb was relatively high, in above 20 yuan. m^-2. a^-1, that of the herbaceous was the lowest, only 10.642 yuan. m2. a^-1.(6) The effective measure to increase the ecological value of urban green-land include enlarging the green cover area and and increasing the leaf area vegetation quantity per unit area in industrial districts planting. The one measure was most probable enlarging the green cover area and increasing the vertical greening, the other measure was planting the species with better adaptation and better ecological effect based on the function of green-land. At the same time, the structural type of the shrub+herb, the arbor＋shrub and the arbor＋shrub＋herb should configure to increase the vegetation quantity per unit area. Then, the ecosystem services of green-land will be enhanced and the environment quality of industrial districts will be improved.