Monday, July 9, 2007

IS AHK/China --- Tree Root Disturbance in the name of 'Instant Effect'

*** Station Mail is for the information of Station Members only, but Station Mail has given up copyright & can be freely circulated. For administrative reasons, comments from outsiders are usually not entertained & may be circulated within our system locally & overseas.***

Dear Station Members,

Attached photos show quite a common scene in HK in landscaping.

Mature trees were planted along the street for years & then it was decided to add attraction for certain purposes. Colourful shrubs & groundcovers were added in to make the setting look more like an European garden, which would actually invite constant watering & heavy maintenance. Soil in the vicinities of the Mature Trees were churned over in the name of 'cultivation' since it was regarded to be too compacted for shrub & groundcover growing. Excavator might be deployed for churning which would actually add further compaction to the soil by running over it. Compost would then be mixed in with heavy digging usually to a depth of 300mm to ensure 'proper mixing'. Thousands of shrubs & groundcovers would then be added in to achieve the desired 'Instant Effect'. The job was then appraised to enhance Greenery for our city.

Would the same thing be carried out in Europe, America, Australia, New Zealand or Singapore in a location where Mature Trees were already installed for years ??

Probably not, except for a very good reason. Landscapers & Arborists there would know that digging & churning near Mature Trees would seriously disturb the root system of the established trees. The Absorbing Roots of Mature Trees would usually grow at a depth of 300mm from soil surface & they are fragile. Messing around with them would kill them or seriously disturb their normal functions. On the other hand, the thousands of new shrubs & groundcovers added in will compete with the roots of the Mature Trees for nutrients & water. Smaller plants would usually win due to their massive numbers. The Mature Trees would therefore be depleted of the existing supply.

Mature Trees are like senile human without much vigour to re-generate lost parts when compared to Young Trees (usually those below 100mm DBH for many species). They will have a hard time to re-grow lost roots & re-attain vigour once disturbed. That's why Western Nations would not carry out so many Mature Tree Transplantation like in HK/China. Transplantation will disturb roots, even more seriously than adding shrubs & groundcovers nearby. In a way, we love our trees to death in our city.

The ill-effects of the root disturbance for these Mature Trees would not be felt instantly, but the so called 'Instant Effect' can be because the area around the Mature Trees will become instantly colourful. However, the Mature Trees may develop decay, retarded growth, dieback, internal cracks, cankers & many other problems in the months to come. At one point or another if these Mature Trees are not inspected carefully & regularly after symptoms have developed, the trees may fail in the rainstorm. Then we may call it an 'Act of God' . Nobody would then get the blame.

It would be much better if these colourful shrubs could be added at the same time when the trees were planted years ago to give the tree roots time to accommodate. Even so, it is always recommended that a layer of mulch to be placed under the canopy of the trees to provide healthy growth for the roots. Roots of trees & shrubs/groundcovers do compete for nutrients & water with one another.

Are we really knowledgeable enough in our planting intelligence as we'd like to think we are, when compared to the rest of the advanced world ??

best regards,

Sammy Au
Station Manager


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