11.08.2015 - von Christian Lingnau

15. How much CO2 can one tree absorb from the atmosphere?

Unfortunately, this is a rather difficult question, as it cannot be answered easily. Relating to the rainforests, these trees do not only grow way faster than the ones within the tempered climate zone, but also bind more CO2. But even German forests differ greatly: the development and combination of trees vary to a great extent based upon the regional soil characteristics and the climate. Saving capacity differs greatly amongst all various tree species. Therefore, we rely on rather conservative data and base our calculation on insights from the forestry sector. A simple, traditional tool is for example Reinhard Schober’s yield chart (Ertragstafeln wichtiger Baumarten bei verschiedener Durchforstung, Sauerländer 1995, ISBN: 3-7939-0730-9). The database has been established with the help of researching within realistic testing areas. You can find values for an entire growth performance starting from the planting up to the harvesting. These values equal the sum of the previously used amount of wood and the timber reserves of the remaining trees. Taking the beech tree as an example, this value is 1.297 cubic metre woods per ha after 150 years.

Dividing this value by the age of the stand you’ll get the average increase of the entire growth rate per annum. Taking the example of the beech tree again: this would lead to a result of 8.6 cubic metre woods. Nonetheless, this value only represents the amount that is relevant relating to tree bark with a diameter above 7cm. However, it is proven that thinner wood is able to bind CO2, too. The whole annual growing biomass is approximately 1/3 bigger. In order to calculate the weight of the biomass, the volume and the timber specific density without the contained water (dry density) have to be identified. Coming back to our example, the dry density of the beech tree is 0.68 t/m3 (vgl. Hanno Sachsse, Einheimische Nutzhölzer und ihre Bestimmung nach makroskopischen Merkmalen Hamburg/Berlin: Verlag Paul Parey 1984, ISBN: 3-490-07916-7). As one half of the biomass consists of carbon, the calculation is to multiply the mass of carbon with a factor of 3.67.

Our CO2 calculator helps us to identify the ability to bind CO2 of all planted trees in proportion to the ability to bind CO2 of the total stock. However, due to the process of natural selection, not all trees will ‘survive’ until the very end. Hence, we are dividing the average annual bound mass by the amount of the originally planted trees.

Once again, our example: the initial stock within the yield chart displays 6.403 beech trees in total. The basis of our calculation is therefore the value of the averaged proportionate bound CO2 regarding a single day. But since there are plenty of different kinds of trees, every single type displays its own calculation basis. We are currently working with beech trees, oak trees, ashes, pines and sycamore.

You can use THIS link to download the entire report – in German. Please keep the license agreement for further distribution in mind!

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