Monday, March 10, 2008

ISA HK/China --- 'The Root of the Problem' by James Urban

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Dear Station Members,

This Station apologizes to bombard our Station Members lately with various kind of research, but arboriculture is just full of research. In fact, if the Station Manager is not working or tree climbing, he will be burying himself in the latest research. There is just too much an Arborist would need to learn to stay in practice to handle the ever changing situation. Obtaining a credential is merely pushing open the gate.

Attached is an article recently given to this Station by the internationally acclaimed Mr. James Urban who will be visiting HK very soon. Mr. Urban needs little introduction as an internationally renowned Landscape Architect & Urban Forester to anyone knowledgeable in the landscape practice. His article here was meant for sharing with our 610 no. of Station Members for our update on the latest international practice on tree production & nursery stock standards.

This article would challenge our conventional wisdom of using Containerized Trees & plants which have been advocated by a lot of our local landscapers to be without 'Transplant Shock' & would give 'Instant Effect' after planting. However, Mr. Urban reckoned that nearly any kind of Containerization would lead to the development of Circling/Girdling Roots, which can lead to future poor growth or even toppling in wind if unchecked. Mr. Urban also reckoned to use Bare Root Trees to avoid this problem.

On the other hand, a new nursery stocks standard has been jointly developed by the ISA, American Nursery & Landscape Association (ANLA) & the American Society of Landscape Architects (ASLA) in 2005 to state that a minimum of two main roots must be within 3 inches of the rootball soil line as measured 4 inches from the trunk, for any nursery tree to be acceptable in urban planting. Further information on this topic can be obtained at :

It is also reckoned that an inch of soil can be left over the roots to avoid damaging the root surface during the planting operation.

In ETF, tree production has been following the above-mentioned practice since the beginning of operation in 2005. ISA's guidelines for tree production are not to have Girdling Roots nor deeply planted roots, & the minimum rootball size should be around 10 x trunk diameter. Containerization is discouraged in ETF to avoid any tendency to produce Girdling Roots. Uphill potting of seedlings at ETF is inspected every week to ensure no Circling Roots development, or to be planted into ground once circling began to appear. Any tree found planted too deep in ETF will be removed & replaced.

Such are the requirements to produce any quality trees, & quality trees would save maintenance & minimize future failure in a landscape. These are also the points ignored by our brothers & sisters up north because their landscape specifications have no requirements up to this level. HK can certainly do better than that.

The attached article was written by an international Landscape Architect on the latest research & finding. It should serve as a good reference by our local landscapers to help source & install our trees, as well as to match our current practice with the world. HK is an international city where visitors can compare, & we have regular storms & typhoons every year. Having better trees would provide better & safer landscape, & our city is wealthy enough to select better trees. HK is Third World no more.

Do we not agree?

best regards,

Sammy Au
Station Manager

The ISA Mission - Through research, technology, and education, promote the professional practice of arboriculture and foster a greater public awareness of the benefits of trees. (

1 comment:

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