Measurement And Evaluation On Green Quantity Of Major Greening Tree Species In Lanzhou

Green quantity, as a new city greening index, shows the correlation of green area or green three-dimension volume and plant's ecological function and explains the ecological benefit of plant function and green area function by measuring the area of leaves or volume of green stems and leaves according to the transformation and utilization of ecological energy and physiological function of stems and leaves. Comparing with the two-dimension greening indexes, the green quantity more accurately reflects the reasonableness of plant structure and ecological benefit level of green area system. It is also a greening and quantitative index of major research in many countries at present.Cedrus deodara, Platycladus orientalis, Sophora japonica, Fraxinus chinensis, Forsythia suspense, Euonymus japonicus and Polygonum aubertii, as major greening tree species of Lanzhou, play an important role improving eco-environment of Lanzhou city. The research on their green quantity becomes an important quantitative index in judging their ecological benefit. The paper comes out some results by analyzing the solid geometry shapes and internal structure for tree crowns of Cedrus deodara, Platycladus orientalis, Sophora japonica, Fraxinus chinensis, Forsythia suspense, Euonymus japonicus in different growing environments of Lanzhou and by calculating and comparing their annual average green quantity and green quantity of different growing month, diameter at breast height (DBH) and size structure. The results showed as follows:1. The internal structure of a tree crown affects its green quantity. The internal structure of a tree crown of the different trees differs obviously and mainly in the volume of non-leave space in the tree crown. The features of internal structure which makes green quantity distribute unevenly in the tree crown directly affects green quantity. The result of measurement shows that Cedrus deodara has no non-leave space in the tree crown, the volume of Platycladus orientalis's non-leave space occupies 70% of its tree crown, the volume of Sophora japonica's 47%, Fraxinus chinensis 27%, Forsythia suspense 7%, and Euonymus japonicus 30%. Because of the different volume of the non-leave space and the shape feature of leaves and so on, the green quantity of the trees that have equal volume of tree crowns differs obviously.2. The different green term and growing month of a tree affect its green quantity. As far as Cedrus deodara, Platycladus orientalis, Sophora japonica and Fraxinus chinensis are concerned, even if they have same DBH and size structure, their annual average green quantity has obvious difference. The green quantity of them are: Platycladus orientalis>Cedrus deodara's>Fraxinus chinensis's>Sophora japonica's. One of the reasons is their different green term. The result of measurement shows that the green term of Cedrus deodara and Platycladus orientalis is 356 days, but that of Sophora japonica and Fraxinus chinensis is 220 days. The green quantity of a tree has obvious difference in different growing month of a year. The green quantity has parabolic relationship with the growing month. July and August is leave's growing peak of Cedrus deodara, Platycladus orientalis, Sophora japonica, Fraxinus chinensis, Forsythia suspense and Euonymus japonicus, and their green quantity is also the most in the same year.3. The DBH of a tree affects its green quantity. The result of research shows that the green quantity of Cedrus deodara, Platycladus orientalis, Sophora japonica and Fraxinus chinensis has straight-linear relationship with their DBHs. As far as Cedrus deodara, Platycladus orientalis, Sophora japonica and Fraxinus chinensis are concerned, even if they have same DBH, their green quantity also differs obviously. The green quantity of Platycladus orientalis is bigger than that of Cedrus deodara's, and of Fraxinus chinensis bigger than Sophora japonica's.4. The size structure of a tree affects its green quantity. The result of research shows that their green quantity has straight-linear relationship with their size structure. As far as Cedrus deodara, Platycladus orientalis, Sophora japonica and Fraxinus chinensis are concerned, even if they have same size structure, the green quantity of them are Fraxinus chinensis > Cedrus deodara's > Platycladus orientalis's > Sophora japonica's >Forsythia suspense's. As far as Forsythia suspense and Euonymus japonicus are concerned, even if they have same size structure, the green quantity of them are Euonymus japonicus >Forsythia suspense's. Therefore, usually, the green quantity of arbor is bigger than that of the bush's.5. The green quantity of Polygonum aubertii,as a cane plant, can't compare with other trees (except comparing their green quantity according to their age structure). But the result of research shows that its green quantity is very little.6.According to the calculating and comparing, green quantity of Cedrus deodara, Platycladus orientalis, Sophora japonica, Fraxinus chinensis, Forsythia suspense, Euonymus japonicus and Polygonum aubertii and the relationship between some factors, such as green term, month, DBH, size structure and so on and green quantity, it suggests that both plant's disposition and space structure of green area and selection of tree species and nursery stock size should be considered when the city green area is built with a amount of green quantity, and that in the process of city greening evergreen trees, trees with more green quantity and nursery stocks with bigger size should primarily be selected to increase green quantity of city and landscape benefit of season's changing, besides that arbor being principal, combined with bush and grass, stereo greening and house top greening to be increased as well to disclose colorful three-dimension space landscape benefit.