What topping is
Topping means cutting the main stems and large limbs of a tree back to stubs, without regard to where a suitable live lateral sits. It is sold as making a tree safer, smaller and more manageable. It achieves none of those things on a mature tree, and it makes the first one materially worse.
What happens next
Year one. The tree has lost most of its foliage — its entire means of producing food — in a single event. It responds by mobilising stored reserves and pushing out a dense flush of epicormic shoots from dormant buds just beneath the bark around the cut. Growth is fast, because it is a survival response.
Years two and three. Those shoots put on length quickly, and within two or three seasons the tree is often back to something near its original height, denser and bushier than before. Meanwhile the stub cuts, which have no collar and no way to seal, are decaying inward from every cut face.
Years four and five onwards. The new shoots are attached only to the outer layers of wood around the cut, not anchored into the stem the way an original branch is. They are now several metres long, heavy, and growing out of decaying wood. This is the failure mode: a substantial limb, high up, tearing out in a moderate wind and landing where the original branch never would have.
So the tree is the same height, considerably weaker, structurally uglier, and now needs the same treatment again every few years to control regrowth. It is a maintenance liability created out of a stable tree.
The other costs
A topped eucalypt loses most of its amenity value permanently — the natural form does not come back. On a protected tree, severe pruning without consent is an offence in its own right, and the North Shore councils, Ku-ring-gai and Willoughby in particular, do pursue it. And a tree in decline from topping frequently ends up removed within a decade, at full removal cost.
What to do instead
If the concern is a specific limb, remove that limb properly at the collar. If the concern is end weight and leverage, reduce over-extended branches back to suitable live laterals large enough to take over as the new leader — that is reduction pruning and it is a different operation entirely. If the concern is falling deadwood, deadwood it. If the tree genuinely cannot be retained, apply to remove it and plant something appropriate in its place.
The good pruning article covers where a cut should go. For a second opinion on a tree somebody wants to top, ring (02) 9090 4915. More on the blog.
Frequently asked questions
Someone quoted me to cut my gum in half. Should I take it?
No. A crew willing to remove half the live crown of a mature eucalypt in one visit is either inexperienced or indifferent to the outcome, and on a protected tree they are exposing you to enforcement as well. Get a second opinion that explains what the actual risk is and proposes work proportionate to it.
Is topping ever appropriate?
Rarely, and only in specific circumstances — a tree scheduled for removal that has to be made safe in stages, or occasionally a species that pollards well and has been managed that way from young. It is never appropriate as routine size control on a mature eucalypt, which is how it is almost always sold.