Hedgerow planting as linear habitat in the metric

Hedgerows are measured in metres, not in hectares, and they sit in their own module of the statutory biodiversity metric. That is why hedgerow biodiversity net gain has its own arithmetic: you can hold a 10 per cent gain in area habitats and still fail on hedgerow units if you remove a length of native hedge and replace it with a shorter run of whips. On a small site, hedgerow planting is often the most practical way to deliver the gain, because a hedge takes up little land and reaches target condition faster than most created habitats.

Why hedgerows are counted separately

The metric has three modules: area habitats, hedgerows and other linear features, and watercourses. Each has to balance on its own terms under the trading rules, so hedgerow losses have to be compensated with hedgerow units.

Length is measured along the centreline of the hedge, in metres. Distinctiveness depends on the type, with native species-rich hedgerows scoring above native species-poor ones, and hedgerows with trees scoring above those without. Condition is then assessed against a set of criteria, and the two together produce the units.

The practical result for a self-builder is simple. Grubbing out 40 metres of old native hedge for a driveway creates a hole in the hedgerow module that only hedgerow work can fill.

The condition criteria and how they are scored

Hedgerow condition is assessed against criteria covering the structure and the ground beneath it. An ecologist walks the length and scores each one, and the number of criteria passed sets the condition band.

• Height and width, with a continuous canopy rather than a line of isolated shrubs.
• Gappiness, measured as the proportion of the length with gaps at the base and through the body of the hedge.
• Undisturbed ground and perennial vegetation in a margin either side, free of cultivation, spraying and compaction.
• Absence of damage from heavy machinery, livestock poaching or persistent tight flailing.
• Limited cover of non-native and invasive species.
• Connectivity to other habitat at one or both ends.

The margin criterion is the one most often failed on new developments, because a hedge planted tight against a fence line and mown to the base on both sides cannot reach good condition however well it grows. Leave a strip of rough grass on at least one side and say so on the landscape plan.

Gapping up an existing hedge against planting a new one

Improving an existing hedgerow and creating a new one are treated differently, and improvement usually wins on the numbers.

Gapping up means planting into the gaps with the same species already present, protecting the base from mowing and stock, and moving to a cutting rotation that lets the hedge thicken. The metric rewards this because the structure already exists.

New planting earns its place where there is no existing line to improve, or where a boundary needs a hedge for other reasons. Both routes need protecting during construction, and clearance before an application rarely helps. Clearing a site before you apply sets out what that costs in metric terms and in enforcement risk.

Species mix, spacing and establishment

Use a native mix suited to the local area and to the soil, taken from what already grows in the hedges nearby rather than from a catalogue. Hawthorn and blackthorn carry most hedges, with hazel, field maple, dogwood, guelder rose, holly, spindle and dog rose adding the species richness the metric measures.

A double staggered row at about five plants per metre is the normal specification for a new hedge, planted as bare root whips between November and March while the plants are dormant. Guards and matting deal with rabbits and competition from grass, and the first two summers decide survival more than anything else.

Three points get missed on small sites.

1. Order the planting for the winter after practical completion of groundworks, not for whenever the contractor is free.
2. Write watering in the first two seasons into the landscape specification, because a dry spring kills more whips than anything else.
3. Specify replacement of failures for at least five years, with a stated survival rate.

Species-rich planting is what lifts distinctiveness, so a five species minimum in the mix, with no single species dominating, is worth writing into the schedule. A Landscape Strategy is the document where that specification sits alongside the rest of the planting.

Trees in the hedge line and how they are counted

Individual trees within a hedgerow are recorded in the metric as individual trees in their own right, and the hedgerow type then reflects whether trees are present. They are not counted twice.

Retained hedgerow trees need root protection areas established under BS 5837:2012 and shown on the tree protection plan, which usually means the construction exclusion fencing runs wider than the hedge itself. A Tree Survey should pick these up, and the fencing line has to be agreed before the first machine arrives.

Planting standards for new hedgerow trees are a different specification again, and they need enough space to develop a crown without being cut back into the flail line every three years.

Management that reaches and holds target condition

The condition band you are promising is the one the hedge has to reach, so the management plan has to be capable of producing it. That means cutting on a rotation of two or three years rather than annually, cutting in late winter after berries have been used, incremental raising of the cut height so the hedge thickens upwards, and no cutting between 1 March and 31 August when birds are nesting.

Thirty years of that has to be funded and allocated. On a single plot the owner does it. On anything larger, a management company or a landowner takes it on through a section 106 obligation, and the schedule should name the operation, the frequency and the season rather than referring generally to good practice.

Councils increasingly ask for the hedgerow module to be shown separately in the metric summary, so present the length lost, the length retained and the length created or improved as three figures rather than burying them in a spreadsheet tab.

An illustrative example: 60 metres of gappy native hedge along a plot boundary, gapped up with hawthorn, hazel and field maple, given a two metre rough grass margin on the field side and moved to a three year cutting rotation, can shift from poor to moderate or good condition within the monitoring period at a fraction of the cost of new planting elsewhere.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it.

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