Thursday, 15 September 2011

Major Cuts

Far from the latest denizen of destruction for the social safety net this article focuses on one of the most destructive practices in pruning. Removing large limbs or whole stems is destructive and can lead to major tree failures. This can be in the short term or even more dangerous, in the distant future.

The scenario usually involves a structure, like a home or garage that is being built or added on to, realizing the beauty and utility of a stately mature tree the home owner decides to locate the addition close to an existing tree. The dialog usually goes like this

” I would like to build X right next to this tree and the builder says that that major limb has to go so it won’t hit the roof/wall/door”. “I need to have this 14 inch limb removed 10 feet up in this 60 foot maple tree”. What I would like to reply is “Can you move the garage over to the other side of the property where there are no trees? “ But not wanting to come off as a smart Alec I will try to explain the consequences.

Making major cuts on the main stem of a healthy tree opens the trunk up to invasion by wood decay organisms and creates structural instability in the entire tree. Trees prevent decay by compartmentalizing the damaged wood. They produce rot resistant barriers using chemicals that the tree fabricates at considerable expense. The tree doesn’t head out to the hardware store and buy turpentine or stain it literally makes it! It doesn’t put it all on the credit card either however it uses its precious energy stores to create these protective bio chemicals. Then it concentrates these protectors in cells near the injury. Once these cells have been used as protective barriers they die and become nonfunctional to the tree. It is a very energy expensive process. These protective zones can be hundreds or even thousands of cells deep. They disrupt the normal flow of nutrients and the tree has to grow over them to close the wound. This will take many years and when it has grown over, the tree will have a large hidden defect that can break unexpectedly. The results can be catastrophic not only for the tree but for the structure that has been built so close to the compromised tree.

There is good evidence and many studies that also show that the removal of large limbs causes internal stress that can crack the interior wood of the tree and weaken its structural integrity. In nature major limbs rarely break and when they do as a result of extraordinary force, they break far away from the trunk and prevent decay from entering the main stem. Many times after storms the trees that fail are ones that have been pruned drastically low on the trunk in the past. Please consider all the options, including complete removal, before making these types of cuts. The practice of painting wounds is not first aid and would require an entire article to explain why it often does more harm than good.

If you are considering construction close to mature trees contact your ISA Certified Arborist to develop comprehensive pruning plan.