Studies on Casual Factors and their Management of Tree Falling by Typhoon at Taipei Areas

• Main Authors: Zoen-Wing Leung, 梁臻穎
• Other Authors: 孫岩章
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/v42bcm

碩士 === 國立臺灣大學 === 植物醫學碩士學位學程 === 106 === A flexible Plant Health Care program, PHC, has to consider the difference and extreme climates in countries and cities, such as typhoons, in order to manage the urban trees and maintain their functional contributions. Because of the subtropics monsoon and humid climate, five to six typhoons usually attacked the northern Taiwan every summer. Therefore, typhoon is an essential consideration for urban trees management program in Taipei A 3-year study was from 2015 to 2017, to diagnose and survey the wind-fallen trees caused by three typhoons with intensities not lower than moderate at Taipei areas. A total of 637 cases of wind-fallen trees were diagnosed and recorded. The fallen trees were separated into 4 tree falling levels, including 286 fully fallen cases (44.90%), 132 trunk broken cases (29.04%), 146 twig broken cases (22.91%), and 20 leaning cases (3.13%). Among 637 cases, the dominant tree species in decreasing series, are Chinese banyan (Ficus microcarpa), Benjamin tree (Ficus benjamina), Taiwan golden-rain tree (Koelreuteria elegans), Cajeput tree(Melaleuca leucadendron) and Madagascar almond (Terminalis mantaly H. Perrier). The study tried to reveal the relationship between trees falling levels as well as numbers of trunk broken or twig broken and the maximum wind speed. Results showed that the maximum wind speed played no significant effect on tree falling level or numbers of trunk broken or twig broken. This study, however, discovered that those trees with canopy-width/DBH ratio between 5.00-19.99, or trees with either open shape or sharp canopy shape, are more easily suffered by typhoons. The study also determined the major and minor causal factors of tree falling. The main causal factors usually are trees with too heavy crowns, infected by wood rot fungi, with environmental stress, or with brown root rot disease. The second causal factors are trees with shallow root systems, growing within strong wind field, or attacked by termites. According to the results of Chi-square test and odd ratio analysis, road side trees, trees with shallow root systems, and trees growing with environmental stress, have higher potential for fully falling during typhoons, other than trunk broken or leaning. The survey of efficacy for post-typhoon tree treatment after 3-months or after the next growth season revealed that the present post-typhoon treatment for wind-fallen trees were effective and beneficial for tree vigor recovering. The observed recovered numbers of trees are more than the expected ones, wherever they are growing in one of 4 planting sites. The survey finally suggested that a structural pruning is necessary for yellow flame tree (Peltophorum  pterocarpum), Kassod tree (Cassia siamea), Hong Kong orchid tree (Bauhinia x blakeana Dunn.) after typhoons. The study also focused on the issue of wood rot fungi. After isolating 35 common rot fungi from 52 wind-fallen tree samples, 6 stronger fungi were screened from them by comparing their enzymes activities for lignin and cellulose degradation. Those wood rot fungi were inoculated onto wood chips from 3 tree species for 30 days to determine the weight loss rate caused by the fungi. Results showed that the wood chips showed different level of dry weight loss and different color change. The six selected wood rot fungi can be reisolated and thus fulfilled the rules of Koch’s postulates. In order to find out the most suitable fungicides for wood rot control, a series of experiments were done. Nine fungicides with different action mode or mechanism were chosen and tested each at dilution of 10,000X, to find their mycelium inhibition rates. Then five of them were determined for their half maximum inhibitory and half lethal concentration when each is diluted into 12 serial concentrations in PDA medium, and to test their mycelium inhibition rates against the six wood rot fungi. The study results showed that hexaconazole (10% EC) at 80 ppm, prochloraz (25% EW) at 40 ppm, and propiconazole (25% EC) at 90ppm, are the most effective fungicide formulations for field application. A 50 mL of them were used to spray on maple wood block each for a 200 cm2 wood surface. Results showed that for preventing or curing the wood rot fungi, all three fungicides performed at least a 90% control rate in the field tests.