Start at the base, not the canopy
The canopy is the part everyone looks at, and it is the last part to tell you the truth. A tree can carry a full crown of leaves on a trunk that is two-thirds hollow. Start at the root flare instead: the place where the trunk widens into the ground.
A healthy root flare is visible and flares outward. If the trunk goes straight into the soil like a telephone pole, the flare is buried — often by a grade change, a raised bed, or decades of mulch. Buried flares rot, and girdling roots strangle the tree from underneath. Both are slow problems that end in failure.
Look for fungal conks on or near the base, soft spots you can push a knife into, and cracks running up from the soil line. Any of those plus a target within falling distance is a removal conversation.
The lean that matters
Trees lean for their whole lives, and a lean that developed over thirty years as the tree grew toward light is usually stable. What matters is a lean that appeared recently — during a storm, after a wet spring, or after nearby excavation.
Recent lean plus soil heaving on the opposite side of the trunk means the root plate has begun to fail. That is not a pruning problem and it does not improve with time. If the tree is within falling distance of a house, a car or a path people use, it should come down promptly.
Crotches, seams and included bark
Where two main stems meet at a narrow angle, bark gets trapped between them — included bark. There is no wood holding the two stems together, just a seam. On maples, ornamental pears and willows this is the single most common failure point we see after a storm.
You can spot it as a dark line or a bulge running down between the two stems. A cable or brace can buy time on a valuable tree, but a large included crotch over a roof is usually a removal.
How much dead canopy is too much
Deadwood scattered through the interior is normal in a mature oak and can be pruned out. Dieback that starts at the tips and moves inward, year after year, is different: it usually means the root system is failing or a vascular problem is blocking the crown.
As a rough threshold, more than 30 percent dead canopy puts a tree in decline, and more than 50 percent with no correctable cause is generally terminal. A tree that has been declining for five years and still shows the same pattern will not recover because of fertilizer.
The signs that mean nothing
Fungal growth on the ground near a tree, moss on the north side, a few dead branches in the interior, ants on the trunk, or a hollow in an old wound are not automatically removal criteria. Trees live with all of it. Lichen is not disease. A single year of heavy leaf drop in August is often drought or a seed year.
This is where an on-site assessment earns its keep. The difference between a tree that needs removal and one that needs a pruning visit is not visible in a photograph, and anyone recommending a removal from a photo alone is guessing.