Height is not a hazard
The single most common reason people ring about a tree is that it is big. On the North Shore, where forty-metre blackbutt and blue gum stand over 1930s roofs at Pymble, Gordon and St Ives, that describes a great many perfectly sound trees.
A mature eucalypt that has stood through sixty years of southerly busters is not unstable because it is tall. What makes a tree dangerous is a defect, and defects have signs.
What to actually look for
At the base. Fungal fruiting bodies on the trunk or over the root zone. Cavities, hollows or soft, crumbling wood. Cracked or heaving soil on one side. Roots that have been cut for a driveway, a pool or a trench — root loss on one side is a common precursor to failure years later.
On the trunk. Vertical cracks, particularly running from a union. Bulges or ribs, which often indicate the tree reinforcing around internal decay. Bark that is loose or missing in patches on a live stem.
At the unions. A co-dominant fork where the two stems press against each other with bark trapped between them — included bark — is structurally weak and is the classic failure point. A crack at the base of such a union is serious.
In the canopy. Significant deadwood. Hung-up broken limbs. Branches that have extended far out beyond the rest of the crown. Sudden thinning of foliage, or a dead top.
Anything that has changed. A new lean, a new crack, a limb that has dropped, foliage that went off colour this season. Change is the signal.
What is not a defect
Bark shedding in long ribbons — normal for blue gum and many eucalypts. Small twigs and leaf litter — normal. A hollow that has been there for twenty years with sound wood around it — often habitat rather than hazard. Lichen on the bark — harmless.
Summer limb drop
Eucalypts sometimes shed large, apparently healthy limbs on hot, still days with no wind at all. It is a genuine species behaviour rather than a fault, and it is one reason deadwooding and reduction of over-extended limbs is worth doing on any big gum with something valuable underneath.
What happens after an inspection
Most trees that get inspected do not get removed. The usual outcome is deadwood removal and targeted pruning, sometimes a follow-up inspection in a year. Where there is a real structural failure, an arborist's report is also what supports a council application — which on the North Shore you will almost certainly need. See the permits article.
If something has already failed, the emergency page covers what to do first. Otherwise ring (02) 9090 4915 — looking is free. More on the blog.
Frequently asked questions
Is a leaning tree always dangerous?
No. A tree that has grown into a lean over decades, with even bark and no soil disturbance at the base, is usually stable and has built reaction wood to suit. What matters is change. A lean that appeared after a storm, cracked or heaved soil on the high side, or exposed roots on the low side are all reasons to ring someone quickly.
What do fungal brackets on a trunk mean?
Fruiting bodies mean decay fungi are already established inside the tree, often well advanced by the time they appear externally. Where they occur matters: at the base or on major buttress roots is the most serious position because that is where the loading is. It is not automatically a removal, but it is always worth an inspection.