Monday, August 15, 2011

ISA HK/China --- Tree Topping in School

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Dear Station Members,

It's summer vacation for schools in HK from June to August every year. It is also time for schools to conduct various maintenance work including Tree Pruning, while the students are away.

From experience, it appears that most School Management believe when trees grow too big, branches will fall or the whole tree may topple, to hit anybody or properties below. Therefore, they employ garden contractors to conduct pruning to reduce the crown size, whether it is required scientifically or not. With this traditional prqactice, contractors are busy to trim trees for schools during summer time, & there are hundreds of schools requiring this service every year. The employment of an Arborist to conduct any assessment for health or safety has never been thought necessary, because schools themselves thought they would know better mostly from common sense, as well as to save cost.

Schools in HK today are tight in funding. In order to follow the conventional practice of selecting the cheapest, the decision of employing a contractor to do the tree work is dependent on the lowest bid. It is mostly the garden contractors rather than the Tree Specialist who would get the job at the end. The attached photos as reported by Station Member show the common quality of work so done by the garden contractor who gave the lowest bid in a recent job.

The trees can be seen heavily topped without any valid reason. Section of wood before the Natural Protection Zone (TPZ) will become pest food to grow enough microorganisms to either snap off the wood section to hit a target below, or to penetrate through the TPZ to cause internal decay. Large wounds will never fully close to induce cavity or internal decay to invite future hazards. Epicormic Sprouts will spring up everywhere to deplete storage reserves to falsely represent vigorous growth. Topping is a practice even worst that removing the tree, because it will invite hazards.

In reality, a lot of urban trees in HK are growing healthily enough until they are pruned, & the incorrect pruning is one of the major culprits of why so many urban trees have turned into hazards. Proper pruning takes more than a few seminars or crash courses to learn, & holding credentials does not mean the person can really prune. Pruning goes along with tree climbing, chainsaw us, rigging, Tree Biology & Biomechanics. Failing that would simply be Mother Nature makes the Rules.

Topping appears to be banned by Govt Guidelines in HK today, but a lot of Govt schools are practicing it. Does it in mean the policy is selective on them?
best regards,

Sammy Au
President (Station Manager)
Registered Consulting Arborist no. RCA#497 (
Board Certified Master Arborist / Certified Tree Worker no. HK-0174BT (
Independent Practicing Arborist no. IPA-010908 (

"Providing treatment without in-depth diagnosis & research support is professional misconduct. "

"Casual tree assessor delivers wanton tree assessment. Mother Nature makes the rules."



许多学校会以为树木长大以后必有重枝倒下而压中学生。因此,不论科学与否,他们都会聘请承办商进行树木修剪,减少树冠。抱着如此心态 ,又有多至数百间学校于暑假都有此需要,需要盈利的园景承办商自然会忙于为学校用传统的方法去修剪树木。很少学校会先行聘请树艺师来进行初步评估, 因为他们可能以为他们所知的会比其他人更多,并以为树木修剪只是一般常识而已。

今天香港的学校大部分都资金紧拙。依循以 “愈便宜愈正确”的政策,雇用某承包商做树木工作自然是取决于价低者得。最后通常是由园艺承包商而不是树艺专家取得这份工作。附照为会员所拍,显示了低价者的一般工作质素。

从照片中可以看到很多树木都無由地被严重 "去顶"。在自然保护层 (TPZ) 前的木块将成为害虫食物,而滋生的微生物可令枝条断落而打中下面的目标,或穿透过 TPZ而引起树体腐烂。过大的伤口可能永不关闭而导致蚀洞或内部腐烂, 而招致未来风险。水横枝会到处窜出伪装蓬勃生长,从以大量消耗树体储粮。

事实上,很多香港的市区树木在修剪前都相对健康; 不正确的修剪将许多树木转变成风险危害。

"去顶" 似乎为香港政府的修剪指引所禁,却有很多政府学校不理。是否此指引不能套用于这些学校呢?




顾问树艺师号RCA#497 (

独立执业树艺师号IPA-010908 (

资深树艺师 / 注册攀树师号HK-0174BT (



(以上由羅葉明,注册樹藝師号 HK-0538 翻译。一切内容以英文版本为准。)