Langonnet Forest, France

We cheated and gave you the short answer first! It’s based on the estimate that a cubic metre of wood absorbs just under a ton of CO_{2}.

But really a tree absorbs anywhere between 10 and 40kg of CO_{2} per year on average, depending on a whole host of factors. And it’s all those complex variables that make working out how much CO_{2} a tree absorbs so interesting. So let’s start breaking it down. For fun!

We’ve developed our own scientific methodology to calculate the average absorption of our trees, verified by Bureau Veritas. We’ve done it to help you quantify your contribution towards **global carbon neutrality** and go on a bit about this in our Carbon Manifesto. But now that’s said, let’s get to it!

The chemical composition of wood

The chemical composition of wood doesn’t vary much from tree to tree. (Hooray, one thing that doesn’t change massively in all this!)

Cellulose (C_{6}H_{10}O_{5})_{n} is the main component of the cell walls of trees. It’s a chain of glucose molecules that the tree produces through photosynthesis. We’ll look at how in a minute. Cellulose makes up 50-80% of wood.

50% carbon

42% oxygen

6% hydrogen

1% nitrogen

1% mineral matter

Photo

From the Greek

for « Light »

Synthesis

Greek for

« Putting together »

Plants absorb water and minerals through their roots to make sap.

The sap travels through the tree to the leaves. The leaves absorb CO_{2} and light.

The leaves use chlorophyll and the sun’s energy to convert CO_{2} & water into glucose.

Oxygen is released and the glucose nourishes the tree, transported by the sap.

**Purifying the air as it grows**

Amazingly, to grow by one cubic metre, a tree will purify nearly one million cubic metres of air of its CO_{2} (assuming 0.03 to 0.04% of air is CO_{2}).^{1} Trees are the best.

Now we know how much of a tree is water, we need to remove that from the equation. Because to calculate the carbon content of a tree, we need to know its dry mass. That’s its mass excluding the water.

** Dry mass:** 50% of the tree is the dry mass

** Carbon: ** 47.5% of the dry matter of the tree consists of carbon^{3}

** Water:** 50% of the tree is water (20% of that in the roots)

To do it, let’s use an example. We’ll imagine a 1000kg tree with 100% humidity. Now we know this tree is 500kg water and 500kg dry mass. And we know that 47.5% of that dry mass is carbon. That’s 237.5kg.

Thanks to molar mass ratios, we can break CO_{2} down and find that it takes 3.67kg of CO_{2} to create 1kg of carbon in the tree. That’s because carbon has a molar mass of 12 and oxygen 16. Combined as CO_{2} that’s 44. And 44/12 = 3.67.

So for our tree example, 237.5 × 3.67 = 871.63kg of CO_{2}. Hooray! If we want to know how much it’s absorbed per year, we need to know the age. If it weighs a ton standing, we can guess it’s 30 to 40 years old. So if we assume it's 35 years old, this big boy absorbed **25kg of CO _{2} per year**.

1,000kg of wood

500kg of dry wood

237.5kg of carbon

871.63kg of CO_{2} absorbed

Plant to absorb CO2

absorb most CO

Young trees or old trees? That is the question scientists are still debating. In their youth, trees grow faster so absorb CO_{2} quicker, but in their old age their density is much greater so they can absorb more CO_{2}, as this ** 2014 study in Nature ** demonstrates. As for our trees, these ones below will give you the most bang for your buck when it comes to CO_{2} absorbed over their lifetime.

Our carbon capture calculations have been verified by world-renowned Bureau Veritas. So when you own a tree, you can track the carbon captured over its whole lifetime!

In the end, most of the figures put forward should be taken with great care, but they give an **average range of 10 to 40kg of CO _{2}** absorbed per tree per year over a lifetime.

^{ 1 }* Vade-mecum du forester * , p. 67, XIVth edition, 2016, Forestry Society of Franche-Comté and Eastern Provinces

^{ 2 } Patrick Vallet's thesis is entitled * Impact of different silvicultural strategies on the "carbon sink" function of forest stands. Modeling and simulation at the plot scale *