Thursday, March 6, 2008

ISA HK/China --- 2008 Research on the Benefits of City Trees

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Dear Station Members,

Traditionally in HK & China, trees in landscape are selected mostly for the benefit of flowering. However for a tree, flowering is meant for attracting mammals & insects for reproduction, & flowers are usually on top & edge of a tree to be seen by these creatures, without consideration of human enjoyment. Therefore, if someone rests underneath a tree & looks up, he would see hardly any flower which is usually the case in our urban setting. Flowering also creates debris when the inflorescence & fruits drop, giving hygienic problem & unsightliness. When a 'flowering' tree is not selected properly for a specific growing condition, the tree may not flower, or just flower once only by burning off the remaining energy.

Another conventional criteria in picking a tree would be to match a tree with the name of a place, e.g. Bougainvillea for ' Bougainvillea Court' & Cherry for Cherry Lane, usually without much consideration whether it is the 'Right Tree for the Right Place' & as long as it looks good on paper. Just look at how many Bahinias are planted all over HK in recent years.

The benefits of trees are certainly more than just for flowering & christening a place. Trees regulate temperature, reduce run-off during storm, hide unwanted view, reduce air pollution, enhance ecological balance, promote social & psychological harmony, & many others. Just when trees are selected for flowering alone does not mean the other benefits should be buried & ignored, & there are more reasons to select a tree just for flowering.

The attached research from ISA gave a rarely mentioned benefit of City Trees in promoting the health & stamina of residents by encouraging them to exercise physically. This research has shown that humans enjoy hanging around environment with trees. In older day China, rural villages would almost without exception plant selected tree species around the vicinity. Some said it was for Fung Shui. This Station would reckon it was for better than that, e.g. firewood, food, shade & herbal medicines. Trees there were a necessity then, & hardly for the reason of flowering.

In the Tree Supervision lecture of the Station Manager at CITA, the first question to throw out to challenge the candidates would be whether anyone would enjoy living in a desert. A desert has no tree. The Station Manager has not yet heard anyone replying that they would enjoy living in a place with no tree. Trees are part of our life in the back of our mind, & therefore they should be planted & protected.

If trees are so important, we would need to learn how to design, select, plant, maintain & inspect trees, because if a tree is not properly so done so, it is likely to become a time bomb for our city. Just look at how many tree failures we have after storms & never mind after the regular typhoons. Trees should be selected for more than just flowering, but also for good Structure & Health to stand against wind. The right trees must go into the right places so that we can enjoy their benefits.

In order to do this, the first step is to learn what a 'good' tree should be because planting, maintenance including Structural Pruning, inspection & risk assessment will base upon how to obtain a 'good' tree. Hence it is always the emphasis of this Station in any of arbor introduction to first inform on how a 'good' tree should look & stay like, since everything else will come from & try to imitate that.

Trees in HK are our valuable assets. We appear to be losing them in our continuous development & we should preserve & protect the existing ones. But we shall need to know how. When we plant new trees, we should also re-vitalize our landscape with good quality ones rather than just hunting for the cheapest. The cheapest ones usually cost more in maintenance & lead to public complaint when failed. Our older trees are already history & should be given a dignified retreat. The new ones should be our hope & we must select the right ones, or we'll repeat our past mistakes.

Disagreement? Our existing trees are still better to show the world? Why not try to compare with Singapore & get some answers there ...

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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