The Construction And Application Of Evaluation Index System For Greening Vegetation In Saline Land

Saline land is largely and widely distributed in China. With the high-speed development of economy and the acceleration process of urbanization, a more prominent problem is the shortage of land resources. The reclamation and utilization of tidal flat resources in coastal areas have been speeded up, including the construction of many coastal new cities. Selection of salt-tolerant greening tree species and construction of plant communities are major problems the new cities facing and the latter is the main supporting technology of fast greening. There were different plant communities constructed based on principles of plant suitability or its aesthetics. Plant disposition will directly affect the overall landscape, the ecological stability and the eco-efficiency of green space system.The aritificial vegetation of Dongtan wetland park was selected as an object in this study. Combined with structure characteristics of the plant communities and coastal saline land conditions, evaluation index system for greening vegetation in saline land of coastal areas was established by analytical hierarchy process (AHP) and Delphi technique. The principle of ecology and aesthetics and the theory about community structure and function were used when constructing to provide a scientific basis and reference for the greening of Shanghai and other coastal saline areas. The system contained13evaluation factors belonging to three norms of ecology (overall growth vigour, level of community layers, diversity of species, diversity of life forms, proportion of native tree species), resistance (saline-resisting index, pest-resisting and disease-resisting index, lodging resistance) and landscape (ornamental type and ornamental period, seasonal changes, coordination degree of colors, balance degree of collocation, coverage).Main research results are as follows:(1) On horizontal structure, there were86species of woody plant which belonged to47families,70genera. The Rosaceae contained the most amount which were8families,10genera. The ratio was2.12:1between deciduous and evergreen trees,1.36:1between deciduous and evergreen shrubs,1.77:1between deciduous and evergreen species. The application of evergreen trees and evergreen shrubs were both insufficient, especially the evergreen trees. The ratio was2.07:1between exotic and local species, application of local species was insufficient. The average breast-height diameter of trees was8.64cm and77.27%of trees had breast-height diameter of5-15cm. As most of the trees were in growth stage, the landscape will change significantly as time goes on. The monotonous landscape type and single ecological function as only19species were with high important values (>20%) were not adapted to requirement about community landscape with rich species during the park greening in coastal saline areas.(2) On vertical structure, the arbor-shrub-grass ratio was4.19:4.38:14.15:29. The proportion of tree was too large while proportions of shrub and herb were both too small. There was a serious imbalance between proportions of tree and shrub as the number of trees was slightly lower than that of shrubs.49.21%of samples were two-layer structure and the three-layer structure which conformed to the natural plant community only accounted for30.56%. The plant communities could be divided into5groups of vegetation,12vegetations.(3) On seasonal changes and health condition,42.86%of samples had plant scenery only for two seasons. Plants with bad (1-2) and good (4-5) average growth potential accounted for20.93%and24.42%respectively. Among the plants with good average growth potential, there were9deciduous tree species,4evergreen tree species,5deciduous shrub species,3evergreen shrub species.(4) The proportions of plant communities with low and high ecology scores were both small.57.94%of samples had ecology scores between0.4and0.6. Only2.38%of samples had resistance scores below0.4, while61.51%of samples had resistance scores between0.6and0.8. The resistance scores of samples were generally higher, nearly30%of which were0.8-1. The proportions of plant communities with low and high landscape scores were both small also.49.21%of samples had landscape scores between0.4and0.6. In general, the proportions of plant communities with low and high comprehensive scores were both small, and comprehensive scores of most samples were0.4～0.8, among which plant communities of level Ⅲand Ⅱ accounted for51.98%and38.49%accordingly. (5) There were5recommended communities of level Ⅰ; communities of level Ⅱ and III got low scores on diversity of life forms, ornamental type and ornamental period, seasonal changes; communities of single tree layer occupied a large proportion among communities of level Ⅳ and Ⅴ. Evergreen trees and deciduous trees, fast-growing trees and low-growing trees, shallow-root trees and deep-root trees, tree species and shrub species, plant species with different florescence should be mixed in a strip or line pattern when allocating and colored-leaf and saline-resisting trees such as Prunus cerasifera, Sambucus williamsii’Aurea’ should be used more. No matter what kind of mixed type was used, the ratio of legumes plant such as Amorpha fruticosa and Robinia pseudoacacia should be large while the ratio of Pterocarya stenoptera and Ulmus pumila should be small, only by this way can they benefit each other. Suggestions such as taking the shrubs and trees in the same height when constructing communities, making full use of varieties of ornamental plants, developing and utilizing the local wild plant resources, widening application of native plants and moderating application of alien species were given to increase plant species and construct diverse stratified communities. Only with these ways can we increase the plant diversity of per unit area of green space and enrich urban landscape to satisfy the vision demand of tourists.