Hedgerows offer route to increased carbon sequestration on farms

Accurate ways to measure carbon in hedgerows are emerging

At best they are taken for granted on farms and at worst they are cut back so brutally that the birds, bees and bugs that thrived in and on them lose their sources of food and shelter. But could the ubiquitous hedgerows on farms across Ireland be revalued for their carbon sequestration potential?

Hedgerows cover about 4 per cent of the Irish landscape or 689,000sq km if you use a broad definition of woody boundaries including lines of trees. Yet up until very recently they have been neglected for all the ecosystem services they can provide – from the alleviation of flooding to habitats for small mammals, birds and insects and as a potentially valuable store for carbon on Irish farms.

Shockingly, only about a third of hedgerows in Ireland are in good condition. Historically, many hedgerows were removed by farmers enlarging fields; however, changes to the Common Agricultural Policy (CAP) basic farm payments in 2009 required farmers to replant the same amount of hedges to compensate for any removed.

"The biggest problem with the management of hedgerows on Irish farms is tidiness. People view farmers as bad farmers if they don't cut their hedges," says Catherine Keena, countryside management specialist with Teagasc.


Hedgerow Week

Keena runs Teagasc Hedgerow Week in December which offers advice to farmers on how to maintain their hedgerows.

“Hedgerows should never be cut “short, back and sides”. Hedges need to be kept dense at the base and the top kept as high as possible with flowering thorns left to grow to their natural height every 300 metres or so,” Keena explains. So–called escaped hedges (for example, a line of trees on a boundary) should never be topped, according to Keena, whose main focus is the management of hedgerows for biodiversity.

But now, with much greater focus on the need for farmers to reduce their greenhouse gas (GHG) emissions as part of Ireland’s Climate Action Plan, there is a scramble to identify ways that farmers can – or already do – sequester carbon on their land to allow for a more balanced picture of carbon emissions versus carbon storage in land use.

Teagasc has used satellites and drones to map the overall footprint of hedgerows in Ireland but closer observations on the height, width and density is required to get a more accurate picture of the carbon sequestration of hedgerows.

In 2022, the Ordnance Survey of Ireland (OSI) will publish the first national land cover and habitat map for Ireland which will provide a definitive baseline for hedgerow cover in Ireland. Meanwhile, the Teagasc farm carbon project is doing field work to establish the carbon storage and sequestration rates of different hedgerow types while also looking at the different constituents of each hedgerow (above- and below-ground biomass, leaf litter and soil organic carbon). The hedgerows are also surveyed by drone to create 3D models to calculate the biomass carbon stock based on volume. The aim is that the farm carbon project will then allow calculation of carbon stock in hedgerows at farm level.

“We are developing the methodology to allow us to assess the carbon stocks in hedgerows over time,” explains Lilian O’Sullivan, principal investigator on the farm carbon project, the results of which are due in September 2022.

By the end of 2022 it is expected that the combined work of Teagasc and the OSI will provide accurate baseline data for carbon stored in hedgerows so the Environmental Protection Agency (EPA) can include it in Ireland's annual GHG inventory for the Intergovernmental Panel on Climate Change.

Emissions inventory

Currently, estimates of carbon storage in forestry, croplands grasslands and wetlands (with hedgerows included as landscape features within crop land and grassland categories) are reported in Ireland’s greenhouse gas emissions inventory in Land Use and Land Use Change and Forestry. However. emissions and removals of GHGs associated with land-based activities are not included in the national total emissions figure, according to the EPA.

Researchers have already shown that hedgerows that are wider, thicker and taller sequester more carbon. Older hedgerows are also more valuable for carbon storage and biodiversity than newly-planted ones, which take between 30 and 40 years to store as much carbon as older hedgerows.

The environmental non–governmental organisation Hedgerows Ireland is concerned that not enough focus is being placed on the role of older hedgerows on farms for their roles in biodiversity and carbon sequestration.

"Small changes in hedge-cutting techniques and regimes could double or treble carbon sequestration, according to the latest research. Allowing hedges to grow to two or three metres instead of the prevalent fashion for 1.5 metres would make a big difference and further changes such as three-year rotation of cutting regimes or side cutting only would multiply the benefits," says Alan Moore from Hedgerows Ireland.

Moore also believes that farmers won’t change their approach to managing hedgerows unless these changes are stipulated in the new Common Agricultural Policy (CAP). In particular, Hedgerows Ireland recommends the wording for proposed new eco schemes in the Pillar 1 basic farm payment (called the basic income support for sustainability) in the new CAP should include a basic requirement that hedgerows are left a minimum of two metres high and either side cut only or not cut for the duration of the scheme.

Moore also suggests that more advanced measures for hedgerow quality (species diversity, carbon stored in soil and biomass, etc) should be integrated in the Pillar 2 agri–environmental schemes of the new CAP.

“The unnecessary over-management of hedges is benefitting nobody and wasting valuable resources. Bigger, taller hedges need not look messy or unkempt. When skilfully managed, they can enhance the look of the farm and massively benefit wildlife,” Moore adds.

He contends that the only references to hedgerows in the current draft CAP proposals from the Department of Agriculture, Food and the Marine is to avoid cutting them during the nesting season which is already a statutory requirement under the 1976 Wildlife Act. Ireland's submission on the CAP are due to be sent to the European Commission for scrutiny by January 1st, 2022.

Whatever measures to improve hedgerow management are eventually decided on in the CAP will no doubt be even more important once the European Union certification scheme for carbon farming is introduced by the end of 2022.

Only then will farmers across Europe have clearer opportunities to embark on so-called carbon farming in a way that could transform farming practices both for farmers and for the environment.

Sylvia Thompson

Sylvia Thompson

Sylvia Thompson, a contributor to The Irish Times, writes about health, heritage and the environment