Root flare

The root flare is where the trunk widens just above the ground. It is the transition between trunk and roots. Trees Are Good, from the International Society of Arboriculture, says the trunk flare is where the trunk expands at the base of the tree.

For stumps, the flare matters because it makes the base wider than the trunk above. A stump cut low may show the flare and surface roots. Measuring stump diameter at the widest point can include the flare.

On a living tree, the flare should be visible above the soil. Buried flare is a planting problem, not a stump problem. Buttress roots and surface roots often start in this area.