A Splitting Trunk-Ache: Why Trees With Two Trunks Fail in Strong Winds

Most trees have a single, dominant trunk from which their branches spread outwards. However, some trees develop a second trunk. Tree species such as the elm, often grow a second trunk and sometimes, even several trunks. Unfortunately, a co-dominant tree, i.e. one with two trunks, may endanger you and your family during storms or on windy days.

Co-Dominant Trees are Dangerous

Not all trees with two or more trunks are dangerous. It depends on their age, condition and the weather in your area. These three factors combine to devastating effect if a co-dominant tree is old and in poor condition. All it would take in this instance is a storm with strong winds, and the tree's two trunks would split apart like a wishbone.

Co-dominant trees with U junctions, which give each trunk more room, tend to be more stable than trees with V junctions. When two or more trunks grow tightly packed together, they form a V junction. V junctions allow debris and water to gather at the junction, inviting pests and rot, weakening the area further, while the weight of each branch threatens to split the tree in two.

Wind Is a Threat to Co-Dominant Trees

Young trees can withstand a lot—even young co-dominant trees. They have yet to be damaged by disease, pests or the weather. However, an older tree with a V junction that is rotting from water exposure and bacteria is a sitting duck in a storm. Large trees are especially vulnerable in strong winds due to the weight of both trunks.

It is important to keep a close eye on your tree if you believe it may be a hazard in high winds. This year, in Reading, UK, strong winds snapped one of the trunks of a co-dominant tree. Fortunately, nobody was hurt. However, in Australia, wind can be deadly, as was seen in 2015, when winds of 213km/h brought trees down and wreaked havoc in Sydney.

Is Your Co-Dominant Tree Safe?

In Australia, some of the most powerful storms occur in late autumn, in October and November. Before that time arrives, you should assess your tree. However, only a trained arborist can correctly assess a co-dominant tree and determine whether it is worth saving or not.

Arborists will sometimes prune the branches of a co-dominant tree to reduce the strain on the V junction. Young and healthy trees can be saved with cabling or bracing if necessary. Old or sick trees, however, should be removed because they may split in high winds and endanger you and your family. For more information, contact your local tree removal services. 

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