Sequestering soil carbon by planting hedgerows

Hedgerows, a common feature of farmed landscapes around the world, provide a number of ecosystem services, including the sequestration and storage of atmospheric carbon in both their own vegetation and the soil. However, since the 1960s, there has been a general decline in hedgerow length and condition in most regions of the world, with negative effects on biodiversity and soils. Recently, hedgerow planting and management have been encouraged through public agri-environment schemes and private sector initiatives for nature protection and climate change adaptation and mitigation.

Hedgerow planting goals

The potential of hedgerows to mitigate climate change seems substantial as they can sequester and store carbon in their biomass, as well as in the soil beneath them. Therefore, increasing hedgerow length has been proposed as an option to contribute towards climate change mitigation in several European countries. For example, the Climate Change Committee proposed that the length of hedgerows will need to increase by 40% to contribute towards reaching the UK’s net-zero targets. In England, this would require the planting of approximately 190,000 km of new hedgerows across arable and grassland landscapes, which equates to about half the length of Britain’s road network.

However, the rate of carbon sequestration associated with planting hedgerows has not been accurately determined, and it is unclear to what extent the target of 40% increase in hedgerow length is achievable via current public agri-environment schemes and initiatives that encourage planting.

Quantifying soil carbon sequestration

The University of Leeds is part of the Resilient Dairy Landscapes project funded by the Global Food Security’s Resilience of the UK Food System Programme. As part of this project, researchers quantified the change in soil organic carbon (SOC) stock as a result of planting hedgerows on dairy farms in Cumbria, one of the options offered in the ‘Milk Plan’, a sustainable supply chain initiative run by Nestlé-First Milk.

Professor Pippa Chapman, who led the project, said: “We found that the top 50 cm of soil beneath hedgerows stored, on average, 31% more carbon than the adjacent intensively managed grass fields, with old hedgerows storing almost double that amount. The larger soil organic carbon stocks found beneath older hedgerows compared to young ones indicate that these stocks progressively build up over time, contributing to offsetting emissions.

“Our estimations show that a 40% increase in hedgerow length across England will result in 4.7% of present-day agricultural CO₂ emissions from agriculture being sequestered each year for four decades” said Dr Sofia Biffi, adding “this figure could rise to 6.4% by increasing hedgerow width by just 50cm.”

Private sector funding is needed alongside public funds to ensure that hedgerow planting will contribute towards reaching UK net-zero targets

Professor Guy Ziv

However, the current rate of hedgerow planting funded by agri-environment schemes is too slow to meet a 40% increase in length by 2050. The private-sector initiative that researchers studied showed much higher planting rates, highlighting that private sector funding is needed alongside public funds to ensure that hedgerow planting will contribute towards reaching UK net-zero targets.

Read the briefing note and the journal paper that explore this project in more detail. You can also watch the recording of a webinar about the project.

A further paper extends this research, examining aboveground carbon sequestration, hedgerow planting rates and carbon offsetting potential in England.

What next?

The research will be extended to other regions of England, such as North Yorkshire and Sussex, to determine if soil carbon sequestration and storage through hedgerow planting are influenced by differing climate, soil, and farm types.
Further calculations will quantify the total carbon sequestration rate associated with planting hedgerows by determining the carbon stored in the woody aboveground biomass and how this varies with hedgerow age.
Research data will be used to inform post-Brexit national Environment Land Management schemes, as well as to expand the UK Hedgerow Carbon Code, and a broader Farm and Soil Carbon Code that is being developed.

Professor Pippa Chapman is a soil scientist working in field of land and water management. Her research focuses on how land use change and management practices affect soil processes, nutrient cycling and soil and water quality.

Dr Sofia Biffi is an environmental scientist. Her research falls within agro-ecology and she is interested in agri-environment schemes impact and uptake, farmland biodiversity, and soil properties in sustainable management systems.

Professor Guy Ziv works at the interplay between policy, land management decisions and land use change impacts on ecosystem services. His research focuses on the impacts of policy and climate change on the water-food-energy system and the environment.

Dr Richard Grayson is a hydrologist focussing on hydrological processes and functions within the soil. His research is centered on studying how land management impacts hydrological and geomorphological processes.