After a storm the call is always the same: it came down out of nowhere. Almost always, it did not. The signals were there — they were just above head height, or behind the shed, or so gradual that nobody noticed the lean had changed. Here is what to look for on a walk around your own section.
1. Mushrooms or bracket fungi at the base
This is the one that matters most and the one people most often ignore. Fungal fruiting bodies on the trunk, on a root buttress, or in the soil at the base generally mean decay in the structural wood. The mushroom is the visible part of something that has been working through the tree for years. A tree can look completely healthy in the canopy while its root plate is compromised.
2. A lean that has changed
Plenty of trees lean and always have — coastal trees especially. What matters is change. If a lean is new, or has increased, or if there is fresh soil heaving, cracking or lifting on the opposite side of the base, the root plate is moving. That is an act-now situation, particularly heading into a wet winter.
3. Deadwood in the canopy
Bare branches that never came into leaf, or limbs with no fine twigs left, are dead and will eventually fall. On a tree over a driveway, a deck or a play area, deadwooding is usually the cheapest useful thing that can be done — it removes what would land on someone without altering the tree's shape or health.
4. Cracks, seams and hollow sounds
Vertical cracks or seams down a trunk or through a main union are structural. So is a section that sounds hollow when knocked. Trees do compartmentalise decay and can carry a surprising amount of hollow and stay standing — but the assessment of how much is left is not a guess to make from the ground with no experience.
5. Tight, V-shaped unions with included bark
Where two stems grow up tight against each other in a narrow V, bark gets trapped in the join and the two never properly fuse. Those unions split, usually in a storm, usually taking half the tree. On a young tree it is fixable with formative pruning. On a mature one it may need reduction or cabling.
6. A history of shedding limbs
If a tree has dropped branches more than once, it is telling you something about its structure or its health. Eucalypts are notorious for this — mature gums shed large limbs in hot, still weather with no wind involved at all, which is precisely when people are sitting underneath them.
7. Roots damaged, cut or buried
Trenching for a driveway, a new fence, drainage or a retaining wall regularly severs structural roots on one side of a tree. So does raising the soil level over a root zone, which suffocates it. Failures from root damage often come two to five years after the work that caused them, long after anybody connects the two.
8. Thinning canopy or off-season leaf drop
A canopy that is visibly thinner than the same tree down the street, small pale leaves, or dropping leaves out of season are all signs of stress. Stress alone is not danger, but it is the tree telling you something is wrong at the roots or in the vascular system, and it is worth a look before it becomes structural.
What to do if you see two or three of these
One sign on a tree in the back corner of a large section is worth keeping an eye on. Two or three signs on a tree over a house, a driveway or where people sit is worth an assessment now, before winter rather than after it. Not everything with a warning sign has to come out — a great many are fixed with deadwooding, a reduction to lower the sail area, or simply monitoring. Getting that diagnosis right is the job.