Quick answer: How to Tell If a Tree Is Dangerous — Trees on this coast live with fog, salt, wind and thin soil, and the work that keeps them healthy is decided by those conditions rather than by a calendar written inland. Structure, clearance and the root zone are what a tree here needs looked at, and small work done early is what keeps a tree out of the emergency list.

What it involves: Structural pruning, clearance from structures and wires, deadwood removal, root-zone care and hazard assessment.
Typical timing: Structural work in the dormant months; deadwood, clearance and hazard work whenever the tree needs it.
The standard: The ISA standards for pruning and tree risk assessment, applied by ISA-certified arborists.
Where we work: Cambria, San Simeon, Harmony, Cayucos, Morro Bay, Los Osos and the Cambria pine belt.
Our own record: 503 pages and 291 stories published on this site; Uncategorized (109) is the rail this page files under. Counted from our own archive, not a stock table.

Field note. What we see on this coast is that the trees people worry about are usually not the ones in trouble: the pine with a clean crown and a lean that predates the house is often sounder than the tidy tree that has been quietly drowning in its own root zone.

On the other hand, there is no schedule that suits every tree — the same species on two sides of one street can need opposite care, which is why we look before we recommend.

Standards and sources: Tree care standards (ISA — International Society of Arboriculture) · Pest and disease notes (UC IPM — University of California pest management)
Prepared by Cambria Pines Tree Service Inc. — ISA-certified arborists working on the Central Coast.

Most of what makes a tree risky is visible from the ground, and a homeowner with no training can find it. The point of the exercise is not to replace an arborist — it is to know when to call one, and to be able to describe what you saw.

One: is the base wider than the trunk above it?

Walk to the tree and look at where it meets the ground. A sound tree flares outward — there is a widening, and buttress roots radiating from it. A trunk that goes into the ground like a post has a buried flare, and a buried flare is a slow structural problem.

Look for the flare on the side away from the house as well, because that is the side nobody has planted against.

Two: is there a mushroom at the base?

A fungal fruiting body on the lower trunk is the visible sign of decay inside the stem. It is not a certainty of failure — some conks indicate decay in the heartwood that the outer shell is carrying perfectly well — but it is the finding that most reliably warrants a professional look.

Photograph it. The species of the fungus is diagnostic and the photograph is what an arborist needs.

Three: is the trunk round?

A trunk that has a flat side, a seam, or a vertical depression where two stems pressed together is a trunk with included bark. Included bark means there is no continuous wood across the union, and that union is the one that splits in a wind.

You can usually feel it before you can see it: run a hand around the trunk at chest height and feel for a groove.

Four: are the main limbs attached or embedded?

Look at where the largest branches meet the trunk. A sound union has a collar — a slight swelling of trunk wood around the base of the branch, and a visible ridge of bark. A weak union has the branch going straight into the trunk with bark trapped in the crotch, like two boards pressed together.

Five: has the ground moved?

Soil lifted on one side of the base, a crack in the ground arcing away from the trunk, or a lean that has changed since you last looked. All three mean the root plate has moved, and a moved root plate does not recover.

This is the check that matters most and the one people skip, because it requires remembering what the tree looked like before.

Six: is there deadwood in the crown, and how much?

Some deadwood in a mature crown is normal. A crown that is a third dead, or dead branches concentrated on one side, is a tree that is losing a fight — with drought, with a root problem, or with a pathogen.

Seven: what is underneath it?

A tree with a defect and nothing under it is a curiosity. The same tree over a bedroom, a driveway or a power drop is a different object. Measure the distance from the trunk to the thing it could hit, and compare that with the tree’s height. If the target is inside the fall radius, the tree is worth assessing.

The one you can’t check

The inside of the stem, and the condition of the roots below the surface. That needs either an increment borer, a resistance drill, or an excavation — and it needs someone who can interpret what comes out.

Which is the honest division of labour: the seven checks tell you whether to make the call, and the risk assessment tells you what the call should be. A tree that passes all seven still deserves a professional look if it is large, close to a structure, and has recently changed. A tree that fails one of them deserves one now.