Monday, July 9, 2007

ISA HK/China --- Loving you by Topping you

Dear All,

I was shocked to see this!! Trees growing healthily on the central divider of the Sheung Shui Highway facing Choi Yuen Estate were topped & mutilated in just a few days. These trees have been there for nearly 20 years & their lower limbs were elevated enough to miss the traffic below. They were well formed & majestic. Now they have a fate like as shown. The attached photos give some of the details of their current condition.

What would happen if topping is done to a tree?

1. Structural damage --- The central leader is removed & the tree will grow sideway instead of upright. This is the last thing we want for a street tree. The sideway branching habit will cause obstruction to traffic, property & street lighting. The structure of the tree is destroyed & a potentially hazardous tree is created.

2. Profused sprouting --- The topped tree will try to regain its ability to phtosynthesize by producing massive sprouting at the point of topping. These newly grown sprouts are genetically weakly attached to the branches for a number of years until strong branch union is developed. If at any one time such resprouted branches would grow big enough to attract wind, they may break easily & fall upon pedestrians, traffic & properties. Such profused sprouting is commonly confused with a tree regaining vigor. In fact it is not. It is expending its reserved energy to try to stay alive instead of gaining it. It would make the tree weaker & prone to pathogens attack.

3. Weakened root system --- The roots below will become weakened when the branches above are suddenly removed. In the natural process of shedding, the energy & nutrients from the shedded branches will be first transferred to the other parts of the tree including roots before the shedding would take place. In the case of topping, the stored energy & nutrients are just removed without recycling. The roots below which obtain their photosynthates from the leaves above are just suddenly cut off & starved. Starved roots mean stress & pathogens will find a way for entry. Then the tree would go into decline.

4. Decay --- Proper cuts should always be made at the nodes. Topping would just cut anywhere. The branch protection zones are destroyed. This would open wounds & create stubs as food for the micro-organisms. Decay would spread quickly. Internal cracks & cankers would develop. Insects like borers would quickly find these weakened spots & drill into them. The structure of the tree will be further weakened. Many trees toppled this way after apparently standing still for a few years.

5. Ugly looking --- Who would want to have a tree with branches sticking up to the sky like incense burning on a pot? Would it not be bad Fung Shui for some people?

Above are just the main points. There are also other points. For those of you who would like to further study into the topic, I recommend you to look at:

1. An Illustrated Guide to Pruning, 2nd edition, by Edward Gilman
2. Tree Pruning - A World wide Photo Guide, by Alex Shigo
3. Modern Arboriculture, by Alex Shigo (This one is the heavy weight & is really meant for the real professionals)

All 3 books can be obtained through the Store at the website of ISA ( ISA members will get a sizable discount.

I can see these topped trees might be deemed for transplantation. Since the lorry bed in HK is usually less than 3m in width, the trees were topped in order to fit them on to a lorry for transport. It is also much convenient & cheaper to move a smaller tree than a tree with full crown & large rootball. Therefore it may be done for economic reasons. Then may I ask why think of transplantation for these trees in the first place? The answer may be to 'save' them from felling. So some tree lovers decide to save the trees by topping them. And what may they get at the end? Possibly hazardous trees with potential killing power. Is this not an ambiguous case of "Loving you by slowly killing you"?

I am sure the same event would not happen for a govt project in London, Melbourne or even Singapore these days. It would happen everyday somewhere in China though. Are we so desparately trying to catch up with the practices of our brothers & sisters up north? I thought we have 50 years. That's certainly something we need to think about.

best regards,

Sammy Au
Station Manager

PS: 'Topping' is also called 'Heading' by arborists. The two terms mean exactly the same practice.

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