How rotational hedge management is helping store more carbon

Hedgerows managed on a 12- to 15-year laying rotation store six times more carbon than those flailed annually, studies on a Cornish beef farm have shown.

Overall carbon emissions at Browda, Linkinhorne, stand at 611.13t carbon dioxide equivalent (CO2e), with sequestration calculated at 254.08t.

A total of 19km of hedgerows on the 101ha (250-acre) organic farm – which sits in a deep valley to the east of Bodmin Moor – make up 33.75% of that sequestration.

Woodland, permanent pasture and herbal leys make up the rest.

See also: How silvopasture can help with heat stress

The carbon calculations for Browda were made as part of Cornwall’s five-year Farm Net Zero project (finishing this year).

This involved assessing the hedgerows on each of the 43 farms involved in the project for length, width and type of management.

Farm facts

Browda, Linkinhorne, Cornwall

Roger Halliday © Emily Fleur

• 101ha including 18ha woodland
• Permanent grassland, herbal leys and wholecrop
• Organic since 1999
• 50 pedigree South Devon and Angus-cross sucklers
• Cattle finished off grass at 30 months and supplied to ABP
• 19km hedgerows on earth/stone-faced banks

Small fields

Browda is made up of about 70 fields, of which 40 are 1.6-2.4ha (4-6 acres). It is farmed by Roger Halliday and his wife Lavinia.

The fields are all divided by hedges of mixed species including hawthorn, blackthorn, hazel, spindle and elder, as well as trees such as oak and ash.

Woody plant growth captures carbon as it grows, and carbon is also locked up in root biomass and leaf litter.

“We’ve got more hedges than most, so there’s more carbon capture,” says Roger, adding that hedge divisions allow paddock grazing without the need for electric fencing.

The farm runs a herd of 50 spring-calving pedigree South Devons and Angus cross South Devons. Calves are weaned in late November/early December around housing.

Bulls remain outdoors, and youngstock also stay out to strip-graze forage crops of roots or kale, until the weather turns. Turnout is in mid-March, ahead of calving.

About half the grassland is down to five-year leys comprising five grass species, several herbs, and red and white clovers.

These leys produce one or two cuts of silage a year, providing winter feed alongside a wholecrop of peas, oats and barley.

Boundary hedgerows at Browda © MAG/Judith Tooth

Hedgerow management

The carbon assessments across the project farms indicate management has a significant impact on the ability of the hedges to sequester carbon.

According to Browda’s latest carbon footprint calculation, its 15,885m of large-growth hedgerows, laid every 12-15 years, are capturing 85.7t CO2e – six times more than if they were flailed regularly (13.99t CO2e).

Browda hedgerows growing tall © MAG/Judith Tooth

“[When flailed] hedges have a fraction of the amount of wood, leaf and deadwood,” Roger points out.

Rather than flailing every year or so, the hedges at Browda – most of which are long established – are instead laid on a long rotation as part of the farm’s Countryside Stewardship Mid Tier agreement.

“We use local contractors to do what’s called conservation hedge laying, using chainsaws and covering up to 100m a person a day.

“If we laid them in the traditional craft style, we’d be lucky to cover 10m/day,” explains Roger, adding that without laying, the hedges would deteriorate into gappy hedges and then just rows of trees.

Conservation hedge laying © MAG/Judith Tooth

Costs

The farm’s current agreement started in January 2022, and 6,500m of hedge laying was carried out during the 2022-23 winter.

Mid Tier (capital payment option BN5) contributed £9.40/m to the total £10/m cost of laying. Funding for this work has since increased to £13.52/m, with an estimated cost of about £15/m.

To this is added any consequent fence repair, and Roger’s time and diesel for clearing up after the contractors have completed their work. However, he tries to keep this to a minimum.

“I’m not too tidy about dead matter in hedges and tend to leave it – it provides more bank material, and the decomposing wood is good for insect life and captures carbon,” he says.

While he leaves the hedges to grow upwards between each laying, he opts to cut the sides more frequently.

This means they store less carbon than if they were left to grow freely outwards as well as upwards, but makes the task of laying more manageable.

“We trim the sides every three years – largely for convenience, so there’s less mass to deal with at the next laying. But for wildlife, the bushier the better,” he explains.

This work is also done by contractors and is charged at 11p/m a hedge side, or 22p/m for both sides.

Cut every third year over 12-15 years, he estimates the total cost at about £1/m of hedge, compared with the total cost of around £15/m for laying.

The Mid Tier annual payment (option BE3) pays 13p/m for each side of the hedge.

Hedgerow sides are trimmed every three years © MAG/Judith Tooth

Benefits

A long laying rotation brings many benefits beyond carbon sequestration.

“It keeps a traditional skill going, and the hedges provide landscape and wildlife value, such as improved bird nesting and roosting, increased fruiting and invertebrate populations, and habitat for specialised species such as hazel dormouse,” says Roger.

Wood from hedge laying also provides fuel for a biomass boiler on farm (replacing an oil-fired one). This heats the farmhouse, office and a hospital pen for sick calves.

And with the hedges left to grow up about 5m (on top of the traditional 1.2m high earth-based, stone-faced banks they sit on) before being laid again, they shade the cattle in summer and shelter them when it is wet and windy.

“Managing hedges on a laying cycle can bring such benefits to any farm hedges – not just in Cornwall – although doing this at scale is significantly more expensive than regular flailing and so only likely to be feasible so long as sufficient public funding remains available,” he points out.

Fencing

Although Browda no longer has a resident sheep flock (at 70 years old, Roger has hung up his shepherd’s crook), his son Rob brings sheep from his nearby county council tenanted farm to aid grassland management each summer.

This means stock netting, rather than simple post and wire fencing, is still needed to protect the hedge banks. However, capital payments under Countryside Stewardship also help fund this work.

“We’re moving to using steel fencing in some places. It’s particularly useful in hard-to-access areas such as alongside streams where we can’t use a post driver and where modern treated timber doesn’t last,” Roger adds.

Soil organic matter

Soil tests through the project show an increase in soil organic matter – though he points out change is “a long-term affair”.

“It’s largely down to the livestock we keep and the crops we grow, and the impact of the hedgerows – the roots and the leaf fall – on the adjacent soil.

“You would get this to some extent when flailing, as the cut matter goes onto the ground, but a bigger hedge means more material,” he says.

As bonfires release carbon into the atmosphere, his preference is not to burn the arisings from hedge laying.

“If we’re in, say, a field of herbal ley with no rough corners, we will have a bonfire, but otherwise we’ll make heaps in wet or rough corners or along streams, so the arisings slowly rot down over three to five years,” he says.

“That way, the carbon’s going back into the ground as soil organic matter.”

Cornwall’s Farm Net Zero project is funded by the National Lottery Community Fund and is a partnership project between Duchy College’s Rural Business School, Farm Carbon Toolkit, Westcountry Rivers Trust, Innovative Farmers and Innovation for Agriculture. It concludes in 2025.