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Old trees are treasures that need good care

Joburg and Cape Town’s grand old trees are in the spotlight this Arbor Week (September 1 to 7). Like respected senior citizens, trees planted decades or even centuries ago need continual care to flourish.

With so many trees reaching a ripe old age, a new generation of highly qualified arborists is emerging to offer cutting-edge advice on how to prolong the life of old trees. Arborists specialise in the care of individual trees and are trained in the latest science regarding the needs of trees, as well as being equipped to provide effective care.

“Trees are complex systems,” says arborist John Parker.

“A tree has about 45 000 protein lipid pairs in its DNA strand. Humans have about 23 500,” he adds.

Recommended by the Tree Society of South Africa, Parker qualified in arboriculture in Australia and has worked on trees across the world. He now operates as the Tree Guru and works on projects around the country.

“Trees have been fighting disease and injury for 160 million years, using a strategy called compartmentalisation,” Parker explains. Understanding how trees defend themselves is an important foundation for understanding how to care for old trees.

“Compartmentalisation of Disease in Trees (CODIT) is a system first described by tree scientist Dr Alex Shigo. It refers to a process whereby trees use walls or chemical barriers to enclose a wound site to limit the spread of pathogens and associated rot,” says Parker.

“At a wound site, chemical compounds are deposited and form a defence barrier to stop and limit the progression of the rot, fungus or pathogens into the rest of the healthy tree.

“There are nine positions in the tree where a barrier response, to protect the tree against injury or disease, occurs. Chemical in nature, these barriers are found in various places in a tree such as roots, or at leaf nodes where they can quickly seal wounds left by leaves that fall off a deciduous tree in autumn.

“One of the most important barriers is found at the ‘branch collar’, the place where the branch of a tree grows out of the main stem, or trunk. It is described as a collar as it looks like a shirt collar which is narrow on the branch (neck) and thickens out on the trunk wood (shoulders),” Parker says.

“Another way of understanding what the branch collar looks like is to take a look at your hand. Extend your thumb outwards. The collar looks just like that flared part joining your thumb to your hand. In fact, the crease one sees between the thumb and hand is exactly like the branch bark ridge found on branch collars.”

This branch collar is also known as the Branch Defence Zone (BDZ).

“The chemical barrier gets more concentrated over time, which means that barriers can increase and strengthen as the tree ages,” explains Parker.

Why is it important to know about the BDZ? If you prune a branch to a spot in front of the branch collar, your tree will recover. If you cut into the branch collar, you compromise the survival of the tree.

What advice does Parker offer gardeners for dealing with old trees?

Consider these tips this weekend:

KAY MONTGOMERY, Weekend Argus and Saturday Star

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