The tree you are probably looking at
Smooth bark, salmon to orange after the summer shed, twisting horizontal limbs, growing straight out of a sandstone crevice with no visible soil. That is Angophora costata, the Sydney red gum, and it is the defining canopy tree of the Hawkesbury sandstone country that most of the Sutherland Shire sits on.
It is not a true eucalypt, though it looks like one and behaves similarly. It is long-lived, it supports an enormous amount of local wildlife, and Sutherland Shire Council protects it accordingly.
Roots without soil
On a sandstone ridge or a slope down toward Port Hacking, a mature angophora is anchored in cracks and shallow soil pockets rather than deep ground. The root system spreads very wide and very shallow.
That has three consequences. The tree is more vulnerable after prolonged rain, because the shallow soil saturates and loses grip while the canopy is at its heaviest. Root damage from trenching, paving or fill near the trunk is disproportionately serious, because there is no deep root system to fall back on. And stump grinding an angophora is limited by rock rather than by machine.
Summer limb drop
The behaviour that generates most calls. Mature angophoras shed large horizontal limbs in hot, still weather — often late afternoon on a 35 degree day with no wind at all. The mechanism is not fully settled, but the pattern is well known to anyone who works these trees.
There is no reliable way to predict which limb. There are ways to reduce the odds and the consequences:
- Deadwood the canopy. Dead limbs come down first and they come down without warning.
- Reduce end weight on long horizontal limbs. Shortening the outer portion back to a suitable lateral lowers the leverage at the union.
- Move the target. If the limb is over a trampoline or a parking spot, sometimes the cheapest fix is not the tree.
What does not help is topping it, which is covered in the article on topping.
Do not treat bark shed as a problem
Angophoras drop bark in long ribbons through summer, exposing fresh orange trunk underneath. People ring about it every year. It is normal and it is a sign of a healthy tree. So is seasonal leaf drop and the sticky flower fall in early summer.
Signs that actually matter — root plate movement, basal decay, included bark in a fork — are covered in the failure risk article.
Removal is not the default
Where an angophora is sound, the right answer is nearly always pruning and leaving it there. It is a protected native canopy tree, the approval path is not a formality, and replacing a 25 metre tree takes eighty years.
Where one is genuinely failing, the removal page explains the method on rock and on slopes, and Gymea and Caringbah cover the local access issues. Call (02) 9538 7974 for a look.