The cut is everything
A tree cannot heal a wound. It compartmentalises it - building chemical and physical walls around the damage to keep decay out of sound wood. Whether that works depends almost entirely on where the cut was made.
Get it right and the wound closes over a few seasons with a clean ring of callus. Get it wrong and you have opened a channel into the stem that will never close.
The branch collar
At the base of every branch is a slightly swollen ring where branch tissue meets stem tissue. This is the branch collar, and it contains the cells that produce the callus that closes the wound.
Cut outside it and the tree closes over. Cut through it - a flush cut against the trunk - and you have removed the tissue that does the work, leaving a wound that stays open for years.
Just above the collar on the upper side there is usually a raised ridge of bark, the branch bark ridge. The correct cut runs from just outside the ridge down to just outside the collar, angled slightly away from the stem.
The three-cut method
Any branch heavy enough to tear needs three cuts.
First, an undercut about a third of the way through from below, 200 to 300mm out from the collar. Second, a top cut a few centimetres further out, which lets the branch fall without the bark peeling - the undercut stops the tear. Third, the final cut at the collar on a stub that now weighs nothing.
Skipping the first cut is the single most common cause of a long strip of bark torn down the trunk, which is far worse damage than the pruning itself.
Reduction cuts
When shortening a limb rather than removing it, cut back to a living lateral branch at least a third the diameter of the limb being cut. That lateral takes over as the new terminal and keeps sap flowing to the end.
Cut back to a lateral that is too small, or to nothing at all, and the remaining stub dies back. That is lopping, and it is the origin of most of the hazardous regrowth people ring about years later.
How much, and when
No more than about a quarter of the live canopy in a season on an established tree, and less on a mature or stressed one. Leaves are the tree's energy supply; removing too many forces it onto reserves.
In south-east Queensland the general window for structural work is late winter into early spring. Timing is covered here, and the operations themselves here.
Tools and safety
Bypass secateurs for anything under 20mm, loppers to about 40mm, a pruning saw beyond that. Sharp tools make clean cuts; blunt ones crush and tear. Clean between trees if you are cutting anything diseased.
For chainsaw work: helmet with face screen and hearing protection, cut-resistant trousers, gloves, boots. And a hard rule that is worth keeping - if the cut is above your shoulder, or you need a ladder to reach it, it is a job for someone on a rope with training.
When to call an arborist
Anything requiring height access, anything near power lines, anything on a tree you cannot reach from the ground, and anything where a limb could land on a structure. Ring (07) 5408 6029, or read what proper lopping and pruning work involves.
Frequently asked questions
Where exactly do I cut a branch?
Just outside the branch collar - the swollen ring of tissue where the branch meets the stem. The collar contains the cells that close the wound, so cutting through it removes the tree's ability to respond. Cutting too far out leaves a stub that dies back and lets decay in.
What is the three-cut method?
For any branch heavy enough to tear, make an undercut about a third of the way through, 200 to 300mm out from the collar. Then a top cut slightly further out, which drops the weight cleanly. Then the final cut at the collar on a now-weightless stub. It prevents bark tearing down the trunk.
Should I paint or seal the cut?
No. Wound dressings have been researched repeatedly and do not speed closure or prevent decay. They can trap moisture and slow the tree's own compartmentalisation. Leave the cut clean and open.
What safety gear do I need?
At ground level with hand tools: eye protection, gloves and sturdy boots. With a chainsaw: a helmet with face screen and hearing protection, cut-resistant trousers or chaps, gloves and steel-capped boots. Above ground level you need rope access training and a climbing system, which is where most people should stop and call an arborist.