In ‘The Best Trees for Cairns’ Crazy Weather Part 1’, we discussed the Cairns weather and its effect on trees and looked at the factors that make a tree wind resistant. In this article, we’ll look at the factors that cause trees to be considered unstable and identify the trees that you probably don’t want in your yard.
The factors that constitute trees that are unstable and unsuitable in storms include:
Damaged, sick, old or dehydrated trees – this is pretty self-explanatory. Sick or old trees will be weaker and things like termites (which commonly affect Eucalypts in Cairns) and dehydration can cause trees to break off at the trunk during storms.
Top heavy trees – trees with thick or heavy foliage and crowns generally give too much wind resistance. An example of a top heavy tree would be Fishtail Palms and the exception to this would be heavily foliaged trees with deep taproots, such as Mango
Poor root systems – large, strong taproots are key to ensuring a tree remains in the ground. Trees with shallow root systems frequently topple during cyclones, but it’s not just the species that determines the integrity of the root system – the quality of soil and frequency of watering during development plays a huge part. Trees should be planted out before they are 1 year old and those that are root bound should be planted well away from habitation.
Soil quality and density – If the soil is very sandy or very clay-heavy (which affects developing roots from being able to penetrate the ground properly), the root system will not be strong. Erosion from natural causes or development will also affect the strength of root systems.
No wind stress during development – If a tree does not experience enough exposure to wind during its younger years, its root system will not develop sufficiently. Lack of wind stress can be caused by a tree growing behind a wind break, a tree being staked for too long, a tree that is over 1 metre tall when planted and other similar situations.
Trees planted in rows – Unlike trees planted in clusters (mentioned above), trees planted in rows as a windbreak (i.e., with the row running against the wind, rather than with it) have no protection from in front or behind, so they generally fall.
Badly pruned trees – trees that have not been properly pruned or lopped develop weak points or become unbalanced, leading to a greater chance of falling or dropping branches.
The absolute worst trees to have during a cyclone include, but are not limited to: Caryota urens
(Solitary Fishtail Palm), Citharexylum quadrangulare (Fiddlewood), Corymbia citrifolia (Lemon-scented gum), Corymbia torelliana (Cadaghi), Eucalyptus camaldulensis (River Red Gum), Eucalyptus tereticornis (Forest Red Gum), Grevillea robusta (Southern Silky Oak), Khaya senegalensis (African Mahogany), Peltophorum pterocarpum (Golden/Yellow Flame), Spathodea campanulata (African Tulip Tree), Tabebuia aurea (Golden Trumpet Tree).
The best guidelines for planting in cyclone prone areas like Cairns is simply to not plant large trees near homes or other buildings; however, this is not always practical and you may have existing large trees that you can’t remove. So, your second best bet is to have your trees checked regularly by a professional arborist to ensure they’re healthy and not likely to fall. If your tree is identified as a species likely to fall, an arborist can advise you on what to do to prevent it. Cairns Tree Services can help you with all of this and more, so give us a call and we’ll keep you safe during the next cyclone season.
