ISA HK/China --- HK Tree News (Wanchai and Repulse Bay Tree Failure)

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Dear Station Members,

Attached & below are two recent counts of local Tree Failure worthy for discussion in our Station:

1. Tree Failure in Buk Tai Temple in Wanchai (see attached)

This incident appeared on the local media may be because the fallen branches damaged a temple where prominent citizens are visiting. Other than that, there did not appear to be any significant value in this Tree Failure case when compared to many other Tree Failures on slope all over HK.

What has raised the eyebrow of this Station in this incident would be that this tree was said to be inspected by somebody just 3 months ago before the incident. As trees are developing creatures & they change shape & condition in reaction to the environment, it is very difficult to draw a line to say whether this tree must fail in a certain time. Tree Assessment is always an educational prediction in ISA knowledge so far & ISA HK/China would always recommend a Tree Assessor to possess the basic knwoledge listed in our previous Station Mail (http://isahkchina.blogspot.com/2009/04/isa-hkchina-tree-assessment.html), & not just someone waving credentials. Many Arborists around the world have tried to quantify Tree Assessment but owing to the many factors which can affect the calculation & modeling, not one single method has been adopted by ISA so far to be a universal method for standardization, including the use of Detection Tools for Decay determination (http://isahkchina.blogspot.com/2009/04/isa-hkchina-2009-isa-research-on-tools.html).

The Station Manger recently became involved with a similar case of Tree Failure somewhere in Kowloon leading to a law suit for property damages. He has issued a +20 page Expert Witness Report on the incident to comment on responsibilities & liabilities of the opposite side. This just shows that there is always a legal risk involved in carrying out any Tree Assessment if the damages can not be settled between the two parties, & Arborist is frequently the tool to provide independent opinion on the incident.

Let's hope it would not be the case for this one.

2. Tree Failure in Repulse Bay (see below)

This appeared to be a typical case of the client wanting a 'flowering' tree to be grown in his/her compound & expected the tree roots to grow to the centre of the Earth to hold the tree against wind.

It can be seen from the photos given that there were hardly any roots adequate for anchorage, yet the tree had developed a full crown above to attract wind. Then when adequate wind pressure exerted on the crown, the tree body simply toppled over like a domino card.

In Arboriculture, we always say it is 'Mother Nature makes the Rules, not anybody' for Tree Planting. A tree may be planted there for 'flowering, scent or Instant Effect', but it will be Mother Nature to determine whether this tree is going to last, & would fail it when conditions are met.

Would the public be willing to listen to the Arborists gradually?

best regards,

Sammy Au
Station Manager

"If a tree is not designed, installed, maintained & inspected properly, it is likely to become a liability rather than an asset."

"Trees are good for the community. Trees need care like human beings. Arborists are the Tree Care Professionals."

淺水灣塌10米鳳凰木險壓學童

(x報)2009年9月12日 星期六

【x報專訊】毗鄰國際學校的港島淺水灣別墅，昨晨有一棵逾10米高的鳳凰木塌下，粗壯枝椏擊毁數輛薄餅店外賣電單車。附近保安員稱，事發前有學童行經，幸沒被壓倒，否則恐重演塌樹殺人慘劇。香港大學地理系講座教授詹志勇指大樹被埋在「層層疊」的石屎層中，令根部組織壞死，最終不勝負荷「齊口」折斷。

毗鄰國際校 兩學生剛行經

倒塌的鳳凰木逾10米高，樹幹直徑近一米，根部被直徑兩米的花崗岩包圍，植於淺水灣道78至80號的淺水灣別墅範圍內，屬私人管理樹木。屋苑保安員稱，該樹每年都有專人修剪樹椏和除蟲。街坊對大樹突然塌下深感可惜，但慶幸未有造成傷亡，「隔籬商場有一間國際學校，很多學前幼童上學，塌樹前就有兩個學生行過，好彩避得過，否則壓死人」。

事發昨晨9時許，巨大的鳳凰木突然向海灘道35號商場方向塌下，壓毁兩道鐵閘，數米長的樹椏擊向薄餅店的外賣電單車，車尾外賣箱被打穿。消防員到場搜索後證實無人受傷或被困。

學者﹕樹根埋石屎層 嚴重蛀蝕

現場所見，鳳凰木樹根連著花崗岩砌成的底座「齊口」折斷，中間露出一個近半米的樹洞。有「樹醫生」之稱的專家詹志勇看過相片後指出，該鳳凰木樹齡30多年，樹根已被真菌嚴重蛀蝕，雖然仍能維持表面的枝葉繁盛，但其生長環境十分惡劣，「塌下是遲早的事」。

他指出，樹根是埋在不同新舊的石屎層下，顯然是在不同年份有人用「一層又一層石屎疊上去」，卻令樹根埋在十分堅硬的泥土中，無法吸收養分和空氣，新根不長，老根被真菌蛀蝕，結果必會承受不了樹身重量塌下。

由政務司長唐英年統率的樹木管理專責委員會於今年6月發表報告，因私人財產受到《基本法》保障，故認為不宜立法監管私人土地上的樹木。詹志勇認為，「石屎封樹」在公共及私人場所均十分常見，容易發生意外，「最重要是種樹前考慮到樹木會長大，並訂出長遠計劃」。

放大
逾10米高的鳳凰木倒塌後，可見其底部與花崗岩砌成的底座一起「齊口」折斷。
放大
鳳凰木塌下，粗壯的樹椏折斷跌入圍牆後，數輛薄餅店外賣電單車被擊中損毁。