I can see the headlines: TREE KILLS MAN. Yeah right. It should read; Man spends hours under tree renound for dropping large limbs without warning (and gets squashed). But then less newspapers would sell. And it takes up more space. As always there is more to it than meets the eye.
In my experience trees generally don’t drop limbs or even fall over by themselves. Many dead river red gums have sat around for decades in water seemingly immovable. Tough and resiliant and in just about every sunset photo of Lake Bonney.
In severly burnt areas native vegetation can be burnt and recover or be burnt and die but still not fall over or drop large limbs. As gardens generally get smaller and less very large trees are planted any limbs dropping is increasingly becoming an unusual event. In fact most of us in the Riverland and Mallee would consider any tree over ten metres as being fairly large.
Trees I see in this area that are at risk of dropping limbs and large ones at that fall into two categories.
The first I’ll call cultural. That is, species selection, soil suitability to the plant, the health of the plants at planting and subsequent treatment such as watering frequency. As an example, take a Eucalyptus globulus or Tasmanian blue gum which can grow to sixty metres high. Given enough water it will grow guickly and look fantastic but in our 250mm annual rainfall as a maturing tree it will quickly run out of water for sustained growth and will shed leaves and then limbs to stay alive. Many other high rainfall species of trees will act in the same way. Insect attack such as borers can weaken an already weakened tree to the point where limbs will drop. These things will stress the tree and what you will be looking for is a noticably thinning crown (much like men really), insect attack and shooting from the base or near the base. Just because a tree is stressed doesn’t automatically mean that it will start to drop limbs but it would be one to watch. ‘Before and after’ photos can be of great assistance when deciding how much a tree has degraded over say a year or two.
The second category I’ll call species specific. That is, species that drop limbs fairly regularly and often without warning. You won’t see a sign at the bottom of the tree ‘ Large limb will fall to ground to the south west at 7.45am’. Borers may or may not be present. Limbs that have previously fallen may or may not be present. They may be growing in a cultivated garden or in the paddock or even in natural vegetation. They will drop limbs as the proverbial thief in the night comes. Not even nessesarily at night. Thankfully at least in the Riverland and mallee these species and restricted to just two plants. They are common and are worth knowing simply from the point of view of avoiding long peroids of time spent under them.
The first is Eucalyptus cladocalyx or sugar gum native to the Flinders Ranges and Kangaroo Island was widely planted for shade and shelter from the late 1800’s and typically the predominant shade trees in most state schools. They can be seen in large numbers in the Adelaide park lands and locally an impressive stand on the northern side of the Old Sturt Highway at Berri Estates.
The second and probably the even more significant species is Eucalyptus camaldulensis or river red gum. Sometimes called widow maker. It occurs in every mainland state of Australia usually along water courses. Most of us in the Riverland can spend lengthy periods near, around and sometimes under these magnificent trees, all too often unaware of the small but non the less significant risk we take. Many that have spent time on the river can relate one story or another of a river red dropping a limb. If you don’t see it, all you will hear is a sickening crack and fractions of a second later an even more sickening ground shaking thud or massive splash.
The simple message is don’t be there.
If you don’t know what a sugar gum or a red gum is, ask someone that does. Then avoid spending any length of time under them. If you don’t want to be squashed.
Incidently, both these trees make great woodlot trees to produce high quality firewood, but that is another story.
This article first published in the Riverland Weekly © March 12, 2009.