Sunday, November 18, 2007

ISA HK/China --- HK Tree News (Metal Tree Grills, Power Line Pruning & Scorching)

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Dear Station Members,

Attached are 3 sets of recent Tree News in our territory for your interesting reading:

1. Metal Tree Grills

Residents wrote in to complain about the Tree Grills obstructing root growth & inducing tree failure. From the photos so shown, it can be seen that the roots were over-growing the Tree Grills & girdled around them.

Interesting enough in the Arborist education seen by this Station so far, there is hardly any information for or against the use of Tree Grills in planting a tree. From common sense, an Arborist would understand that a Tree Grill made of heavy metal would compact the soil underneath by its own weight or by pedestrians trampling over it. Having a dead weight on top of the root system in times of vibration by traffic or nearby construction would lead to downward compaction, especially when the soil is wet with rain or irrigation. If the species chosen would develop plank roots like those shown in the photos, the Tree Grill would simply become an obstacle for root expansion. Obviously if the Tree Grill is engulfed & girdled by developing roots at the root collar region, the effect would be like sliding a knife across the root collar. The constriction point will become the weakest link & toppling can then be expected in wind.

This Station has recently seen public parks abandoning the use of Tree Grills & placing sand cover as the uppermost layer on top of the root system. Some critics may say sand can be easily dispersed when walked upon. However, sand would lead to lower compaction & transmit water & oxygen better. Sand also would not obstruct root growth.

Organic mulch seems to be the most popular choice as top cover in a lot of Western tree planting. However, some critics in our territory would say that dry mulch can be a fire hazard.

Then what should we use as best?

2. Trees Obstructing Power Lines

Someone complained about tree removal or topping by the management next to the overhead transmission of LRT in Tuen Mun. The management explained that the action was in consideration of safety.

An Arborist would be interested to find out whether the trees were planted before the installation of the overhead transmission or after in order to make a judgment. If before, then it can be viewed that the trees or species were incorrectly chosen not considering the future expansion of trees to contact the power lines. If after, then it may be a case of unfortunate incidence because no one could foresee the overhead lines would be placed there.

If a tree is not designed, selected, installed, maintained & inspected properly, it is likely to become a liability rather than an asset. The trees in this case may have witnessed this saying & ended up being removed or topped.

Sad story.

3. Tree Scorching in Crematory

Tree were scorched by being too close to the burners. This happed to the Wishing Tree in Tai Po in which the tree was scorched by burning incense underneath. Most tropical trees can not be burnt to stay well in this manner.

Once again, this is another case of chicken & egg situation of whether the trees were there first before the burners or after. If after, then apparently little consideration or respect had been given to the trees. Or the trees might have been naturally propagated there by nature. An Arborist just can not make a decision without finding more.

Arborists are Tree Doctors & Tree Detectives. Arborists must be fact-finding & truth-telling in his work with Integrity & Professionalism.

Then can we now say that we do not need Arborists in our community as an profession extra ?

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. (

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