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Climate friendly hedges capture carbon

Ruth Ruddell, Sustainable Land Management Branch, CAFRE

The Northern Ireland landscape is a patchwork of features shaped over many years by farming practice of which, hedgerows are a prominent feature. Northern Ireland has the highest density of field boundaries in the UK which the Countryside Survey 2000 estimated there are about 118,000 km present in Northern Ireland.

A hedge has many and varied roles as part of the farm business, traditionally for marking ownership boundaries, for stock proofing fields and providing shelter for livestock from inclement weather and the sun. More recently a wider range of benefits from hedgerows are recognised such as; a dense good sized hedge improves biosecurity by forming a physical barrier to reduce disease spread in livestock via ‘nose to nose’ contact; they prevent soil loss from erosion; reduce water pollution by intercepting nutrient run off; and also connecting habitats to benefit wildlife.

Furthermore, hedgerows are being recognised for their role in alleviating climate change by capturing carbon dioxide and storing it as carbon in woody growth, roots, leaf litter and soil organic matter beneath the ground (also known as carbon sequestration). Increasing hedgerows has been identified as one of the key changes needed to reach ‘net-zero carbon by 2050’ the UK’s contribution to stopping global warming.

We can work towards this goal by looking at how we manage existing hedgerows on the farm; generally the higher and wider the hedge the more carbon it will sequester and store. Research suggests that a tree line will sequester treble the amount of an annually trimmed hedge. Also, switching internal field boundaries to a three year rotation of incremental trimming ensures there is a range of widths, heights and hedge density and is proven to increase carbon sequestration. This means that instead of cutting all hedges annually, only one third of hedges are cut and they are allowed to become wider and taller at each cutting thereby increasing their carbon store. The only exception being roadside hedges, where there is a health and safety risk to road users. 

Another approach that can help with a climate friendly hedge is to retain hedgerow trees or to leave a mature whitethorn or blackthorn tree every 300m along the hedge which will also increase long-term carbon capture. As woodland cover is currently low in Northern Ireland, hedgerow trees are increasingly important. Having a variety of species present in the hedge can help with climate resilience as changing weather patterns will affect various hedge species differently over time.

Improvements made to existing gappy or poor condition hedges may be done by coppicing and inter-planting or hedge laying if suitable. This will help restore vigour and density to the hedge which will increase its carbon storage capacity.

Where it will be suitable on your farm, planting a new hedgerow will help with the need to increase hedgerows. November to March is the best time to plant hedgerows on the farm. If planting a new length of hedge this winter, avoid planting during periods of frost and snow. Agri-environment scheme participants should check their agreement to find out how much planting they should carry out and check the information sheets for specifications.

The combination of new planting, hedgerow restoration, 3 year incremental cutting and additional hedgerows trees can cumulatively help work towards net zero carbon.