Why is planting trees helping to reduce climate change?

There are two ways of reducing the amount of CO₂ in the atmosphere. We can emit less CO₂ – and we can remove CO₂ from the atmosphere and store it. Trees can do both! Forests have a key role in regulating the climate, because trees by their photosynthesis absorb CO₂ from the atmosphere and store carbon as wood and organic matter in the soil.

Photosynthesis
Using the energy from sunlight green leaves absorb CO₂ from the air. Inside the leaf cells CO₂ is bound together with water and converted into the sugar substance glucose. Glucose is transformed by the tree to wood, branches, fruit, leaves, roots etc. In this way, CO₂ is bound inside the tree as carbon. There is only one waste substance – oxygen.

Photosynthesis:  CO₂ + Water + Sunlight → Sugar + Oxygen

Respiration
It is only the green parts of a plant that can perform photosynthesis. All other parts of the tree “breathe” – or respire – like animals and other organisms without photosynthesis. In darkness the whole tree respires.

Respiration:  Sugar + Oxygen → CO₂ + Water + Energy

Growth and CO₂ capture
As long as a tree grows, it will absorb more CO₂ than it delivers via its breathing. When a tree is fully grown it reaches a stable level where it respires as much as it does photosynthesis. Once the tree is old and deteriorating it will release more CO₂ than the what is absorbed in photosynthesis. When the tree is completely decayed all the CO₂ bound in the tree will have been returned to the atmosphere.


Forestry and CO₂ storage
Forestry is a way for people to take an active role in the carbon cycle. We can plant trees that absorb CO₂ – and harvest trees when they are mature and absorb less CO₂ than they release. If we plant new trees every time one is cut, the trees we are removing from the forest are CO₂-neutral. If we plant trees on a larger area than originally harvested, we initiate a greater absorption of CO₂ – as well as greater storage of CO₂.

Research at the Swedish Agricultural University shows that the faster a forest grows, the more CO₂ is absorbed. From a climate point of view, it is better to cultivate the forest and make use of the trees rather than “leaving it alone” – provided of course that the forest is managed sustainably and  that all necessary environmental concerns are taken in the production of timber. It is important to remember that there also is a need for old growth forest.

The trees we fell and extract contain a lot of carbon. This carbon can be stored for many years in wood products.

The table below lists how much CO₂ and carbon that is stored in an average tree at different ages:

Beech Tonnes carbon Tonnes CO2	20 years 0,056 0,0205	70 years 0.69 2,48	100 years 1,66 6,08
Norway Spruce Tonnes carbon Tonnes CO2	20 years 0,016 0,061	70 years 1,180 4,300

Food for thought
A Dane emit on average about 10 tonnes of CO₂ a year. A mature tree contains on average 5 tonnes of CO₂. Very simplified we can say that we each must plant two trees per year to be CO₂ neutral. However: It takes quite a few planted trees to get one large tree that is mature for felling.