Wednesday, September 26, 2007

ISA HK/China --- Pruning Guidelines of ETWB Feb 07

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Dear Station Members,

This Station received a useful Pruning Guidelines so printed under with 'ETWB Feb 2007' in the attachment from a Station Member (not a Civil Servant !). This Station has reviewed the contents & found nothing of a confidential nature harmful to anybody, & would anticipate this kind of information may be included into the landscape specifications later for Govt contracts.

The contents of the Guidelines are similar to the knowledge of ISA education on pruning, except they are much simplified for some reasons. In fact, if a Certified Arborist (CA) would look closely at the Guidelines, he/she may find some of the information is taking a similar approach with the book "An Illustrated Guide to Pruning, 2nd edition --- E Gilman" which tends to be a standard text of CA to study day-to-day pruning work. However, the Guidelines have also remained traditional terminologies like Formative Pruning, Crown Lifting, Cleaning, etc. & missed out on Crown Restoration & Mature Tree Pruning which are both vital & relevant to our Topping problem & OVT maintenance in our city.

Another issue that this Pruning Guidelines did not mention specifically is the pruning techniques for Decurrent (without a Central Leader) Trees which have been commonly grown for flowering in the past in HK. A lot of these Decurrent Trees have by now reached maturity & many of them can not be pruned in the same manner as Excurrent (with a Central Leader) Trees. Examples of Decurrent Trees would include the common Ficuses, Bauhinias, Delonix & Lagerstroemias which are common in our city. The species of Delonix regia (Flame tree) would grow fast & tall, & would usually fail without much warning.

To a lot of experienced CA & Tree Farmers, pruning is a vast & complex subject to master. Some say it would take a year to learn proper pruning & a lifetime to perfect. The Station Manager himself goes to ETF every weekend to care for his 20,000 trees & the majority of the time would be spent on Structural Pruning. In nursery production, borer attack is a common pest problem which would kill off the Central Leader of a tree like Topping. Crown Restoration is necessary to re-build the Central Leader or the tree can not be sold.

In a lot of Tree Inspection & Risk Assessment, the recommendation in the Arborist Report would include mitigation measure like Corrective Pruning. This kind of recommendation must be given very carefully because once cut at the wrong places, the tree may suffer by offsetting wind balance or nutrition uptake ability, & the cut parts can not be re-attached by any means.

This Station rarely gives instruction on the subject of Pruning in Station Mail, because we worry that someone may read the information & decide he/she would know it all. Pruning is a 3-dimensional practice & every tree has a different geometry. What is shown on books is usually 2-dimensional only & branch structure is usually not given in details. The Station Manager has always found before pruning is to be discussed, subjects like Tree Biology, Biomechanics & Nursery Standards should first be consulted to understand where to cut & how much to cut. The Arborist should first ask him/herself some questions before carrying out any pruning: Why should I prune, where & & how much to prune. There are times for safety reason or others, healthy tissues may be cut off seemingly absurd to laymen, e.g. Directional Pruning in High Voltage Transmission Lines. Those cuts are particularly hard to accept.

Tree Pruning can not ignore the use of Chainsaws. Chainsaw use involves primarily safety, cutting technique & maintenance. Knowledge in arboriculture is usually knitted together like a net. Any part missing will be like a broken net.

The Oct 7 Trip to ETF will be a good time to learn proper pruning on real trees by experienced tutors. There are still about 10 vacancies available at present & may be going fast once this Station Mail is out. If anyone wants to learn pruning on a real 3-D tree, why not come along to see it in action with tuition, rather than pondering it in theory from a 2-D book or computer?

Oct 7 invites you.

best regards,

Sammy Au
Station Manager

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