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By: Per Friis Knudsen


CO2 storage in wood

A new resolution for the GT Asia team is to continue writing our successful articles for our e-newsletter. One of the topics that interests me the most is the storage of CO2; how it is tied up in wood and how the well-being of our forest globally is necessary, so it stays healthy and continues to tie up all that CO2. Wood is one of the keys to a sustainable future. That is not news for our industry and our followers – hopefully, this is what our children learn in school.

Wood is a renewable resource as it is feeding on CO2, water, nutritious soil, and sun rays. Wood store approximately 1 ton of CO2 pr. 1 m3 wood. Wood does not use any machinery to grow and to store CO2 and it is thereby CO2 negative. It can replace other materials that are CO2 positive materials (i.e. manufactured using heavy machinery such as steel and concrete) with e.g. the constructions of housing. The best thing is if we help the forest to stay healthy, it will tie up even more CO2 in the wood.


How can wood help save the environment?

Most air pollution comes from towns and industries, where as a forest usually has a clean environment. A fresh breath of air and far away from polluting factories and towns. However, this has led me to wonder about the connection between the two areas. If that is the case, then the air from the forest, where I get my wood in Denmark, is clean and does not contain air that is severely polluted. However, if I had imported and bought the wood from a country with higher pollution rates, would the wood be just as clean or store more CO2 as the surrounding area is more polluted? This would lead to questions such as “should we plant a forest in very close proximity to a town or industrial area with high levels of pollution?”, “should we plant forests to prevent polluted air from getting into the atmosphere and swirling around and spreading to the clean forest?”, “can we draw a hard line between air that is polluted and air that is not?”, and “is CO2 different in the wood itself with different levels of pollution?”

Looking at a map from Global Forest Watch, China has enormous areas of land covered in trees but unfortunately most of it is in central China, which is far away from the main pollution centers. China has grown its forest by 40% over the last 30 years (Reference). That equals an area of 629,367 km2 and to put it into perspective it is about the area of Texas. I then wonder, how much pollution does this forest collect and store? Does it help China to get cleaner air? Or does all the pollution in this global world enter the atmosphere and spread equally around the world and find a tree to store it in no matter if it is a Red Oak tree in the Appalachian or a Beech tree in Denmark?

With these questions in mind, I called our freelance consultant Krishnanunni Ravindran to ask him about this.


1) Would it help to plant more trees near very polluted areas (urban and industrial areas) to absorb the CO2 emissions at an early stage in order to prevent the CO2 to get into the atmosphere?

Yes, growing trees in towns and industrial areas can significantly address the problem of urban air pollution. Trees can absorb CO2 and other toxic particles, odors, and pollutant gases, thereby effectively filtering these chemicals from the air. Trees growing in the street proximity can absorb more pollutant gases than distant trees growing miles away from the source of pollution. Thus, trees absorb CO2 from the atmosphere and release oxygen in return through the process of photosynthesis. Depending on the attributes of the tree; species, age, leaf type, canopy structure etc. and the environmental conditions, the amount of CO2 absorbed by trees may differ. Some trees are sensitive to the changing environmental conditions and absorb different amount of CO2 in different seasons. Some are totally insensitive to seasonal changes in environmental conditions and absorb more or less the same amount of CO2 round the year. Thus, planting multiple tree species in urban areas can help in CO2 mitigation and the subsequent climate change.


Sources here & here.


2) We hear terms like CO2, NO2, CH4, and SO2 from time to time, but we always focus on CO2. What are the other elements? Where do they come from and what impact do they have on us? Can they be absorbed? Which of these gases is the biggest problem for the environment?

Apart from CO2, there are a lot of gases in the atmosphere such as nitrogen oxides, ammonia, methane (CH4), sulfur dioxide (SO2), ozone (O3), water vapor (H2O), chloro-fluoro carbons etc. They are released from many natural sources such as volcanoes, decomposition of organic matter, respiration, etc. and from the combustion of fossil fuels. All these gases are now commonly known as greenhouse gases because of the warming effect it has on our environment. Well, these gases are purposely meant for keeping us warm and comfortable on earth. Without these gases in the atmosphere, we would have experienced zero-degree Fahrenheit making life totally impossible on earth. However, a gradual increase in the amount of these gases in the atmosphere could increase the temperature of earth, causing serious problems to mankind.

Out of the many greenhouse gases, CO2 is the largest in concentration and of most concern because of its potential warming effect. Other gases such as SO2, ammonia, nitrous oxides, etc. are also harmful to life when present in amounts beyond the permissible limits. We can of course mitigate some of these gases like CO2, ammonia, nitrous oxides, sulfur dioxides, etc. by planting more trees, which absorbs them through their leaf pores, roots, and bark surfaces. Trees, are therefore, an ideal solution to abate global warming caused by these greenhouse gases.


3) When I burn wood, do I then release the exact same amount of CO2 that was absorbed and stored in the wood in the first place? What is the waste material (ashes) from burned wood?

Trees store carbon in their leaves, trunk, branches, and extensive roots. Also, trees store a significant amount of carbon (around 48%) in the nearby leaf litter and soil. So, not all absorbed CO2 is released upon burning wood.

By burning wood, we unlock the carbon stored in it, releasing it as CO2. The resultant is ash and it is mainly comprised of calcium compounds, potash, phosphate and other hard metals like iron, copper, zinc that the tree absorbs during its lifetime.


4) Is it possible to calculate how much CO2 a km2 of forest can absorb? Example can we calculate how much CO2 storage we lose for each football field of deforestation?

This is difficult to answer as the amount of CO2 absorbed by trees depends on their attributes; species, age, leaf type, size, and the environmental conditions under which they grow. On an average, a mature tree absorbs 22 kilograms or 48 pounds of CO2 annually. However, different studies have given different values, complicating its calculation. Findings from North American forests shows that CO2 uptake by forests is around 0.5 kg per square meter per year. Thus, 1 square kilometer would absorb around 500 tons. This would be far higher for old growth forests compared to forests that have regrown after harvest.


5) One of my favorite things to say is “use more paper and wood – plant more trees.” The meaning is that we should trap and store more CO2 in paper and wood that can be recycled and reused repeatedly. Is there a difference between how much CO2 wood and paper contain?

Carbon remains stored in wood until it is burned or rots, no matter if it is timber or paper pulp. Paper is a processed material, and therefore, it’s production itself cost a lot of emissions. Also, not all paper that ends up in trash are recycled. It is mostly burned, unlocking all the carbon stored in it. Thus, reducing paper use and increasing timber production is what I would recommend for mitigating CO2.

Source here.



What I have learned already in 2022 is to continue my Global Timber New Year resolutions and additionally start recycling more paper. Also, that it sounds like a beautiful thought to plant more forests in and around polluted areas. But how easy is it to carry out and why has it not been done yet? One answer could be that the terrain surrounding some of these areas is not suitable for growing a forest. For example, India and Pakistan have large parts of barren areas where just about nothing can grow. Can we then plant something else instead like bushes to store CO 2 


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