Hedgerow units and the Hedgerows Regulations overlap
The biodiversity metric asks what a hedge is worth in units. The Hedgerows Regulations 1997 ask whether it may be removed at all. The two regimes often give different answers.
Hedgerow units and the Hedgerows Regulations 1997 answer two different questions about the same length of hedge, and a farm or small rural scheme can satisfy one while falling foul of the other. The statutory biodiversity metric asks how much biodiversity value the hedge holds and what must be delivered to replace it. The Regulations ask whether the hedge may lawfully be grubbed out at all.
A hedge can be low distinctiveness in the metric, inexpensive to compensate in units, and still be an important hedgerow whose removal requires a notice to the local planning authority. The reverse also happens. Work both regimes from the start of the layout exercise rather than at the point of submission.
How the metric measures a hedge
Hedgerows are a separate module in the statutory biodiversity metric. They are measured by length in kilometres, not by area, and they carry their own units which sit alongside area habitat units and watercourse units. You cannot offset a hedgerow loss with wildflower grassland, and you cannot offset a watercourse loss with hedge planting.
Distinctiveness follows the hedge type recorded on site. A native species rich hedgerow with trees scores above a native hedgerow, which scores above a line of trees. The species richness threshold is a botanical count made along a defined stretch, so it is a field judgement by someone who can name woody species out of leaf as well as in.
Length is measured along the centreline, and a hedge that runs along a boundary shared with a third party still counts where it sits inside the red line. Where it straddles the boundary, record the position honestly and say so in the biodiversity net gain assessment, because an assessor reading the plan will check.
Condition criteria and why they bite
Condition is assessed against a short list of criteria on a hedgerow condition sheet. They cover the height and width of the managed hedge, the frequency and size of gaps along its length, the width of undisturbed ground and perennial vegetation at the base, the presence of invasive species, and signs of damage from stock, machinery or herbicide drift. The hedge is scored good, moderate or poor according to how many criteria it meets.
Two of those criteria decide most farm hedges. Gappiness is the usual failure, because a hedge flailed hard on a tight rotation develops basal gaps that never close. The undisturbed base strip is the other, because cultivation or spraying to within a metre of the stems removes exactly the structure the criterion is testing for.
That matters commercially in both directions. A poor condition hedge generates fewer units to lose, so removal is less expensive in metric terms. It also generates a low cost enhancement opportunity, because moving an existing hedge from poor to good condition is usually the least costly way to find units on a farm holding.
The separate regime for removal
The Hedgerows Regulations 1997 apply in England and Wales to hedgerows on or adjoining agricultural land, common land, a village green, a site of special scientific interest, a local nature reserve or land used for forestry or horse breeding and keeping. The hedge must be at least 20 metres long, or meet another hedgerow at each end.
If the hedge qualifies, you cannot remove it without first giving the local planning authority a hedgerow removal notice. The authority has six weeks to respond. It may serve a hedgerow retention notice, which prevents removal, and it must do so if the hedge is important under the criteria in the Regulations.
Importance is tested against archaeological and historical criteria and against wildlife and landscape criteria set out in the Regulations. The hedge must be at least 30 years old before those criteria are applied. The historical limb catches hedges marking a parish boundary or recorded on an enclosure award or a pre-1845 map. The wildlife limb turns on woody species counts, associated features such as a ditch or bank, and standard trees.
There is one exemption that matters most on development sites: the Regulations do not bite where the hedgerow is being removed to carry out development for which planning permission has been granted. That is a conditional exemption, not a general one, and it does nothing for work done ahead of a grant.
Where the two regimes disagree
The mismatches are predictable once you see them.
| Situation | Metric view | Regulations view |
|---|---|---|
| Ancient parish boundary hedge, heavily flailed, gappy | Low units, poor condition | Likely important on historical criteria |
| Recently planted hedge of high botanical diversity, well managed | Higher distinctiveness and good condition | Under 30 years old, so importance criteria do not apply |
| Hedge inside a garden curtilage | Units count if inside the red line | Regulations do not apply to domestic land |
| Hedge to be removed under an existing permission | Units must still be compensated | Exempt from the removal notice |
The last row is the one that catches people. A planning permission removes the need for a removal notice. It does not remove the hedgerow units from the metric baseline, and the biodiversity gain condition still has to be satisfied.
Gappy hedges, treelines and what to record
Field calls on classification move the numbers more than anything else in the hedgerow module. A hedge with frequent, wide gaps may no longer read as a continuous hedge at all, and a line of mature trees with no managed shrub layer is recorded as a line of trees rather than a hedgerow with trees.
Record the decision with photographs and a marked plan. An assessor reviewing the metric for the authority can only check what you have shown them, and a classification change made at review stage will move the unit deficit rather than a rounding error.
Where non-native invasive species are present in or under the hedge, the condition criterion fails and separate legal duties follow, which is a good reason to record them properly at the appraisal stage alongside everything else the invasive species duties require.
Creation, enhancement and 30 year management
Hedgerow units are traded against hedgerow units of the same distinctiveness or better. Planting a new native hedge to replace a botanically diverse hedge does not balance the loss, and no amount of area habitat creation will do it either.
The practical options on a rural holding are gapping up and reduced cutting rotations on existing hedges, laying or coppicing where the structure has collapsed, and new planting on field margins. Enhancement usually beats creation on cost, because a hedge that already exists starts from a higher baseline and reaches target condition sooner.
Whatever is proposed has to be secured and managed for at least 30 years. That means a habitat management and monitoring plan with named operations and frequencies, a mechanism binding the land, and monitoring reports at set intervals. The spatial risk position also applies, so off site hedgerow delivery outside the local authority area or the national character area carries a multiplier, as covered in the article on spatial risk multipliers.
Getting both regimes into one submission
Build the evidence once and use it twice. The field visit that records hedge type, length, condition and woody species for the metric is also the visit that gathers what the importance criteria need, provided the surveyor knows to look for the ditch, the bank, the standard trees and the boundary evidence.
An illustrative sequence for a farm diversification scheme: a preliminary ecological appraisal in the spring establishes habitats and hedge lines, a metric baseline is built from the same survey, historic mapping is checked against each hedge to be removed, the layout is revised to retain the two hedges that look important, and the removal notice is avoided entirely because the remaining removals sit inside a permission once granted. The exemptions position, including whether the scheme qualifies for any biodiversity net gain exemption, is settled before the application goes in rather than after.
The metric has to be completed by a competent person under the Environment Act 2021 regime, and the hedgerow condition assessment is a field judgement that a licensed or suitably qualified ecologist should make. This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
Are hedgerow units interchangeable with area habitat units?
No. The statutory metric keeps hedgerows in their own module measured by length in kilometres, and hedgerow losses must be compensated with hedgerow of the same distinctiveness or better. Creating wildflower grassland or woodland will not balance a hedgerow deficit, however many area units it generates on the same site.
Does planning permission override the Hedgerows Regulations 1997?
Where a hedgerow is removed to carry out development for which planning permission has been granted, the removal notice requirement does not apply. That exemption depends on the permission existing first, so clearance carried out ahead of a grant is not covered. The biodiversity gain condition still applies to the units lost.
How old does a hedge have to be to be important?
The importance criteria in the Hedgerows Regulations 1997 are applied only to hedgerows at least 30 years old. Below that age a qualifying hedge still needs a removal notice, but the authority cannot find it important on the archaeological, historical, wildlife or landscape criteria and so cannot serve a retention notice on that basis.
Which condition criteria do farm hedges usually fail?
Gappiness and the undisturbed base strip. Hard flailing on a tight rotation opens basal gaps that do not close, and cultivating or spraying close to the stems removes the perennial vegetation the criterion tests for. Both are fixable through management, which makes condition enhancement a low cost route to units on a holding.
Do I need an ecologist to assess the hedgerows?
In practice yes. Hedge type, species richness and condition are field judgements requiring identification of woody species out of leaf, and the statutory metric must be completed by a competent person under the Environment Act 2021 regime. The same visit can gather the evidence the Regulations importance criteria need.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.