Woodlands and forests contain substantial carbon (C) in the soil, trees and other vegetation, and globally they are hugely important to the carbon, water and energy cycles. Removing forests releases CO₂ into the atmosphere, while growing trees absorb CO₂ from the air. Other greenhouse gases (GHG) such as methane and nitrous oxide are also exchanged between forests and the atmosphere, so forests are a key component of the planet’s GHG balance. Therefore the functioning and management of forests are critical to efforts to reduce climate change (‘climate change mitigation’), and reduce the net GHG emissions into the atmosphere (‘emissions abatement’) including by removing CO₂ from the air (‘greenhouse gas removal’).

UK forest carbon balance

The amount of carbon held in the UK’s 3.2 million hectares of woodlands and forests is estimated at 1,095 Mt C (million tonnes of carbon, or 4,016 million tonnes of CO₂ equivalent).

While the large amounts of carbon in the trees are most obvious to us in the stems, branches and woody roots, about 70% of the carbon held in UK forests is in the soil (calculated only for the top 1m; peat soils in some locations may be much deeper). This very large amount of C in forests is equivalent to about 12 times our present annual UK carbon dioxide emissions, emphasising the role of our forests and woodlands as a carbon store, and how important it is to maintain and expand them.

Importantly, the UK’s woodland and forests are taking up about 4.8 Mt C per year (17.5 Mt CO₂ per year), reducing our net emissions. Expanding the UK woodland and forests will therefore help reduce net GHG emissions. In addition, increasing the amount of C held in long-lived forest products like construction timber will also help sequester carbon, and will help reduce the use of fossil-fuel intensive materials like metals, bricks and concrete.

In addition, harvesting trees for wood fuel for heating or power generation instead of using fossil fuels, can cause a net emissions reduction, if the rate of growth of replacement trees is sufficient to absorb the CO₂ released during wood fuel production and consumption.

Diagram showing the components of the forestry carbon cycle in the forest and outside.

Photosynthesis (green arrow) removes CO₂ from the atmosphere and results in the accumulation of carbon in the woody parts of the trees and the soil; carbon can be lost (red arrows) from the forest through respiration and decomposition, natural disturbances or from harvesting. Harvested wood products can form long-term stores e.g. in construction.