Trees for carbon storage
Through photosynthesis, a tree can remove some 20 kg of carbon dioxide from the air in a year (‘sequestration’). It then stores carbon in its tissues – about half the dry weight of a tree is carbon. Protecting and planting trees are both vital in the fight to mitigate climate change.
We do know that planting can only be part of the effort. Forests in the UK sequester around 20 million tonnes of carbon each year, so protecting existing woodland – and other carbon-holding habitats – is crucial. It goes without saying that cutting greenhouse gas emissions from burning fossil fuels and other sources is paramount, too.
The science behind working out how much carbon trees can eat up is complex, and there is currently no set way for collecting data on the dynamics involved. It is widely accepted that existing woodlands do the most in terms of carbon sequestration, though rates depend on species and soils, for example, and they slow down over time*. Note that carbon sequestration is the process of capturing and storing carbon dioxide from the atmosphere (e.g. at an average rate of 0.02 tons per year), while carbon storage refers to the quantity stored (e.g. 1 ton in a tree aged 50 years).
Trees aren't just carbon sinks. They provide multiple ‘ecosystem services’ (useful functions like reducing flooding), wildlife habitat, food, materials, shade, and just look good! And they make us feel good – as has been recognised in the idea of 'forest bathing'. So plant them for these reasons, too.
If you’re interested in which trees hold the most carbon, here’s a rough guide, based on their average size at maturity in UK conditions. If you are looking for advice on formal carbon credits from tree planting in the UK, please look at the Woodland Carbon Code.
* As highlighted in the Natural England report, Carbon Storage and Sequestration by Habitat 2021
The league table
To put these figures into context, UK annual emissions were estimated at 480 million tonnes in 2020 and our personal carbon footprints stand at 10 tons per year, on average. To give an idea of what this tonnage looks like, a double decker bus weighs around 12 t; an elephant 4 to 6 t.
Around 7 tons at maturity (c. 50-100 years)
Oak: Unsurprisingly, the large and long-lived species Quercus is a top hitter. English oak, red oak, turkey oak and the evergreen holm oak all do a top-notch job. Pin oak is a slightly lighter weight contender.
Sycamore: Sometimes thought of as a bit of a weed, sycamore is actually very good for the environment in terms of carbon storage.
Around 5 tons
Common walnut: Fast growing and large with it, walnut provides storage plus food for humans and wildlife.
Giant and coast redwood: Believe it or not, the huge mass that is a giant sequoia doesn’t hold quite as much carbon as some of our native trees, thanks to its lighter, less dense tissue. Dawn redwood is similar.
Cedar of Lebanon: Stately and superb, cedar of Lebanon is a prime parkland tree that also punches high in the carbon storage stakes.