Effect Of Typhoon Disasters To Urban Landscape Trees And Typhoon Disaster-reducing Strategies In Shenzhen

Typhoon is a kind of strong eddy flow with warm-heart structure, happens in the atmosphere of the tropic sea. It causes serious damage to the landscape of urban green-land in Shenzhen, Jiangmen and other coastal cities, brings a huge of economic loss every year. At the same time, the people's lives and properties are seriously threatened by the trees'lodging and breaking. Attaching the importance to this problem, the government of Shenzhen took the engineering technology measures and established a project to research the disasters-reducing strategies of the green-land in Shenzhen city from in 2000, especially to study how to select the wind-resistance trees and what the relationship between the different cultivating methods and the trees'wind-resistance ability is.This dissertation provided a scientific theory in making the disasters- reducing strategies for Shenzhen green-land, through investigating of the resource of Shenzhen, Jiangmen green-land plants, analyzing the green-land damage caused by typhoon in the resent years, studying the relationship between the trees and the typhoon, and researching the factors that effect the ability of trees'wind-resistance. The results as follows:1. Through the investigation of the street trees in more than 340 streets, and the garden plants in 51 road-greenbelt sample plots in Shenzhen and 40 green-land sample plots in Jiangmen, with the analysis to typhoon disasters, the wind damage index is put forward for first time. The damage degree of the trees which caused by typhoon can be evaluated exactly.After the analysis for the damage of 49 common arbors caused by typhoon in Shenzhen, they are classified to 3 parties by loss degree. There are 8 arbors in the first degree, containing Albizia falcataria, Pterocarpus indicus,Bauhinia blakeana etc. There are 6 arbors in the second degree, containing Swietenia mahagoni, Khaya senegalensis, Dracontomelon duperreanum etc. The loss of the 14 arbors is 49.38% in all trees destructed by the typhoon"Prapiroon". There are 35 arbors in the third degree, containing Bischofia javanica,Terminalia mantaly etc. and it is 40.48% in all trees. The loss of tree species that caused by"Prapiroon"in Shenzhen nearly kept in step with Jiangmen's.2. The factors of the trees lodging and breaking and the measures how to optimize the tree-protecting bracket'functions were put forward through the study of the mechanics that the wind-pressure of typhoon effects on the street trees. After comparative analyzing the ratio between the relative wind-pressure coefficient and the mean diameter at breast height (DBH) of 18 kinds of common street trees and their wind damage index, it is known that the crown size and thickness are the important factors that affect the trees wind-resistance abili3. Through the study of 21 characters of 13 common street trees in Shenzhen by 5 different kinds of clusters and the principal component analysis, it shows that the thickness of crown, the wood's bending strength and root forms are the main factors of the trees wind-resistance ability4. In order to predict the ability of the trees'wind-resistance, the two regression models that take the trees characters as independent variables and take the wind damage index as dependent variable, were established through stepwise and enter regression analysis.Based on the studies above, the typhoon disasters-reducing strategies in Shenzhen urban green-land can be summarized as follows. That is: (1) Selecting wind-resistance trees for urban green-land. (2) Pruning crown correctly and reinforcing the tree-protecting bracket before typhoon approaching. (3) Improving the condition of soil, controlling the soil moisture content and enlarging the planting hole to broaden the living space of the roots. (4) Avoiding frequently changing the urban streets and underground pipe lines, to ensure that the roots grow freely. (5) Seriously controlling the breaking out of the plants diseases and insect pest, improving the trees'wind-resistance ability. (6) Establishing the defense system on the typhoon disasters for the urban green-land.