Main causes of failure.

  • Shallow root system.

Trees and tall shrubs should be planted out when no more than 1 m tall (140mm pot) and should not be root-bound. This gives them a chance to develop a good root system. It is desirable to have a deep watering regime so as to encourage the roots to grow down and not remain on the surface. When planting insert a pipe beside the plant. This should be filled with water weekly to will encourage deep root growth. Once the plant is established then watering should only occur at much longer intervals. Such a regime will not only encourage deep root growth but also encourage roots to go deeper into the soil to seek water as well as saving you work. Frequent light watering of the lawn will encourage the tree/shrub roots to remain closer to the surface and not search deeper into the dirt. Many urban trees that went over had a lot of surface roots extending through the surrounding lawn.

  • Snapped trunks.

This often happens when the root system is strong and the trunk gives away but not the root. Noticed more often when the soil is dry prior to the cyclone striking. The top of the tree snaps incompletely, so that the top while still attached forms a 30 to 40 degree angle to the trunk. If close to the cyclone centre, then it may be twisted off as wind directions change.

  • Sick or old trees or ones with termite damage.

The species most commonly affected are Eucalypts and some wattles, particularly ironbarks. An indication of the presence of termites can be confirmed by drilling a hole into the centre of the trunk. Sick and dying trees usually have dead outer branches and twigs. Drought affected trees will also have the ultimate twigs and branches dead or dying.

  • Top heavy plants

The solitary fishtail palm (Caryota urens) is a good example, the thick crown offers too much wind resistance. Yet mangoes tend to be very good, so there are always exceptions.

  • Erosion

If the root system is undermined by sewer pipes or road development then the tree is unbalanced and will often fall as the root system is not well-developed.

  • Failure of branches

This is nature’s way of self-pruning in times of strong wind, the trunk is saved but branches sacrificed. Badly pruned plants may also behave in this way. Some examples are the Poplar or Cabbage Gum and a lot of the Trumpet Trees (Tabebuia and Handroanthus).

  • Failure of shrubs.

Soft plants with large leaves such as bananas and pawpaws tend to fall as well as top heavy shrubs with shallow root systems. Suggest pruning suitable soft shrubs prior to cyclone arriving. Many recently planted Syzygium spp. In Townsville fell or leant over because the crown was top heavy and the plant had not had time to develop a good root system in situ. Shrubs with multi-stemmed shrubs are usually more resistant as the wind load is spread over a number of stems.

two images of African mahogany

Khaya senegalensis (African Mahogany) has a heavy crown and shallow root system.

Iamges of pine tree bases and fallen fishtail palm

Some tall pine trees and fishtail palms were snapped off at the base.

Images of twisted trunks

Some Eucalypt tree trunks showed evidence of screwing.