How to recognise it
Look at the base of a branch you plan to prune. On the upper side you will often see the branch bark ridge, a raised line of bark running down into the union. Below the branch there is usually a wrinkled bulge, which is the collar. The cut belongs just outside both, following the angle of the ridge, and not parallel to the trunk.
The collar is easiest to see on a branch that has been dead a while and has started to be walled off by the trunk. On many conifers, and on some broadleaf trees, it is less obvious and an arborist reads the ridge and the angle instead.
Why it matters in a dry climate
A tree that closes its own wounds well does not need much help. A tree that is cut flush (flush cut) has the collar removed and a wider wound exposed to decay. A cut left long becomes a stub that dies back. Either way the damage is permanent, because trees do not heal the way people do: they seal wounds off by growing new tissue around them, which is woundwood.
Northern Nevada trees do that sealing on small water budgets. Valley floors get roughly 4 to 10 inches of precipitation a year, so a tree that has to cover a large flush wound is spending resources it does not have. Careful cuts are cheaper for the tree than rescue.
What an arborist does about it
Cuts are made in the right place, in the right order. Large limbs are removed in stages so the bark does not tear down the trunk. Every cut is judged against the collar and the ridge, and the result is checked from the ground.
When an estimate says "pruning", ask whether cuts are made at the collar. If the answer sounds vague, ask who is assessing the work.
Sources
- International Society of Arboriculture, Trees Are Good: Pruning Mature Trees (brochure) (read October 17, 2026)
- NOAA NCEI U.S. Climate Normals 1991-2020, station data (retrieved October 1, 2026)