Tree Work Terms Explained: Crown Reduction, Thinning, Lifting, Pollarding and More
Tree surgeons have their own language. If you do not know it, you cannot check a quote. This page translates the main terms. The definitions come from the Arboricultural Association's terminology guide, which follows the British Standard BS 3998:2010. (Arboricultural Association)
Crown
The crown is the leafy part of the tree: the branches and foliage above the trunk. Most pruning terms describe what happens to the crown.
Crown reduction
"The reduction in height and/or spread of the crown (the foliage bearing portions) of a tree." The tree keeps its main framework and ends up with a similar but smaller outline.
Ask for: the amount in metres, for example "reduce by 2 metres all round". A percentage is less clear because nobody agrees what 100% is.
Good for: a tree that has grown too big for its space, or is too close to a building.
Crown thinning
"The removal of a portion of smaller/tertiary branches, usually at the outer crown, to produce a uniform density of foliage around an evenly spaced branch structure." It does not change the tree's overall size or shape. The guide says removal should not exceed 30% overall.
Ask for: the percentage, for example "thin by 20%".
Good for: letting more light through without making the tree smaller.
Crown lifting
"The removal of the lowest branches and/or preparing of lower branches for future removal." The guide says it should be restricted to less than 15% of the live crown height and should be specified from a fixed point, for example "5.5m clearance above ground level".
Ask for: the clearance height in metres.
Good for: clearing a path, a driveway or a view.
Pollarding
"The initial removal of the top of a young tree at a prescribed height to encourage multistem branching from that point." Once started, it must be repeated on a cycle, cutting back to the same point each time. Many London plane and lime street trees are pollarded.
Ask for: confirmation the tree is already a pollard, or is young enough to start. Pollarding a mature tree that has never been pollarded is not the same thing.
Topping and lopping
"Generally regarded as outdated terminology but still included as part of Planning legislation. Lopping refers to the removal of large side branches and topping refers to the removal of large portions of the crown."
If a quote says this: ask for a crown reduction to BS 3998 instead. Topping leaves large wounds and weak regrowth.
Deadwooding
Removing dead branches. The guide says the aim should be to "leave as much as possible, shortening or removing only those that pose a risk", because deadwood is a wildlife habitat.
Good for: safety over paths and gardens, without changing the tree's shape.
Felling and sectional dismantling
Felling is cutting the tree down. In a small garden it cannot be dropped in one piece. Instead the tree is climbed and taken down in sections, often lowered on ropes. This is "sectional dismantling" or "sectional felling". It takes longer and costs more.
Stump grinding
Using a machine to chew the stump down below ground level, usually 20 to 30cm. The roots are left to rot. Ask how deep, and whether the grindings are removed.
Arisings
The branches, brash and logs produced by the work. Ask whether they are chipped and removed, or left for you.
BS 3998
BS 3998:2010 is the British Standard "Recommendations for Tree Work". The Arboricultural Association names it as the most relevant standard for tree work. Asking for work "to BS 3998" tells the firm you expect correct pruning cuts and no topping.
TPO and section 211 notice
A Tree Preservation Order protects a tree by law. A section 211 notice is the six-week notice you give the council before work on a tree in a conservation area. See our permission guide.
Frequently asked questions
What is the difference between crown reduction and crown thinning?
Reduction makes the tree smaller. Thinning keeps the size but removes some inner branches to let light through.
Is pollarding bad for a tree?
Not if the tree is a species that suits it and the cycle is kept up. Starting to pollard a large, mature tree that has never been pollarded can harm it.
How should I describe the work I want?
Use the standard terms and give amounts: "crown reduce by 2 metres", "crown lift to 5 metres", "thin by 20%". Ask for work to BS 3998.