Risk is target plus likelihood
A tree that might fail into an empty paddock is a low-risk tree. The same tree over a child's bedroom is not. Before assessing the tree, look at what is underneath it and how often someone is there — a driveway used twice a day is a different target to a shed used twice a year.
That is why two identical trees get different advice.
Signs worth acting on
Fresh soil lift or cracking behind the trunk. On a slope, a lifting root plate is the clearest warning there is. Look for a crescent of raised soil or lawn on the uphill side, or a gap opening where the trunk meets the ground. On shallow sandstone soils, this can appear after a wet week and progress quickly. Treat it as urgent — see the emergency page.
Fungal fruiting bodies at the base. Brackets or mushrooms on the butt or major roots indicate decay already well advanced. The visible fruiting body is the last stage, not the first.
A cavity or hollow at the base. Hollows are not automatically fatal — plenty of sound trees are hollow — but a hollow that occupies most of the cross-section, with a thin remaining wall, is different. Camphor laurel is the local species that hollows soonest.
Included bark in a major fork. Where two stems grow up tightly together, bark is trapped between them instead of wood knitting the union. These forks split, usually in the first real wind after a heavy rain when the canopy is loaded with water.
Hangers. A broken limb caught in the canopy will come down eventually, and there is no way to predict when. Get it out.
Previous topping. Weak epicormic unions on decaying stubs, as covered in the article on topping.
Signs that usually mean little
Bark shedding in long ribbons off an angophora or Sydney red gum in summer — normal, and the fresh orange trunk underneath is a sign of health. Brown foliage only on the seaward side of a coastal tree — that is salt burn, covered here. Lichen on the bark. A lean the tree has held for twenty years with no soil movement at the base. Small twig drop after wind.
What you cannot see from the ground
Internal decay, root damage from an old trench, and the condition of unions high in the canopy. Where the target is significant, that is a job for a climbing inspection or a consulting arborist with the right equipment — and where a council application depends on tree condition, an AQF Level 5 arborist report is what carries weight, as covered in the permit article.
If in doubt
Call (02) 9538 7974 and describe what you are seeing. Photographs of the base, the main forks and the whole tree from a distance answer most questions. Nothing on this page substitutes for someone looking at your actual tree.