CO₂ Storage Balance - Making CO₂ emissions from wood use visible
Germany wants to become greenhouse gas neutral by 2045 - forests play an important role in this. On the one hand, they provide the raw material wood, which grows back and can be used to replace CO₂-intensive materials such as steel or concrete as well as energy sources such as coal and natural gas. In this way, we save greenhouse gas emissions that would occur if they were used. On the other hand, the forest itself can be a sink for CO₂ and help to reduce the concentration of greenhouse gases in the atmosphere. This so-called CO₂ sink capacity of the forest increases the less intensively forests are used, i.e. the less wood is harvested. Such effects need to be taken into account when assessing the impact of wood use on greenhouse gas concentrations in the atmosphere.
In greenhouse gas balances of wood products, it is often assumed that wood harvesting has no effect on the CO₂ sink capacity of the forest, i.e. that wood use is "CO₂-neutral". This is a mistake, because a less intensively harvested forest would store more carbon than an intensively managed one.
What is the CO₂ storage balance?
As a growing CO₂ reservoir, the forest itself can contribute to reducing the concentration of greenhouse gases in the atmosphere. This CO₂ storage - also known as CO₂ sink capacity - depends strongly on the intensity of forest management or wood extraction. If wood is used more intensively in the forest, i.e. trees are felled and removed, the CO₂ storage in the forest is reduced. At the same time, there are fewer living trees that could continue to absorb CO₂ - the CO₂ storage capacity decreases. If, on the other hand, the forest is used less intensively, the CO₂ storage capacity increases because more CO₂ is bound in the forest in the form of biomass. We express the interaction of these effects as the CO₂ storage balance. So if we use wood to save greenhouse gases, we have to take such effects into account for the calculation of a total greenhouse gas balance.
The CO₂ storage balance indicates how much the potential CO₂ storage capacity of the forest is reduced by the removal of one cubic metre of wood. It is given in tonnes of CO₂ per cubic metre of wood removed (for example 0.6 t CO₂/m³).
How can the CO₂ storage balance be estimated and how big is it?
If we use the forest less intensively and let trees grow longer, the forest will not be CO₂-neutral, but a sink for carbon. This is especially true for forests that are still young and relatively far from a primeval forest state. The storage balance can be interpreted as a kind of "CO₂ backpack", which shows how much the CO₂ storage capacity is reduced when a cubic metre of wood is harvested. The storage balance can be calculated, for example, by comparing two scenarios in which one scenario assumes more timber harvesting and the other less. More information on the calculation can be found here.
In Germany the CO₂ storage balance amounts to about 600 to 1,700 kilograms or 0.6 to 1.7 tonnes of CO₂ per cubicmeter wood harvested.
What does affect the CO₂ storage balance?
The extent to which wood harvesting affects the CO₂ storage balance depends on a number of factors. The CO₂ storage balance changes over time. It is usually higher for short periods (10-20 years) and decreases when very long periods are considered. The condition of the forest mainly determines how large the effect of the reduced sink capacity is. If the forest is young and grows strongly and has the potential to grow old and to sequester a lot of carbon (e.g. young mixed forests), the CO₂ storage balance is high. In forests that are unstable and have no prospect of storing much more carbon (e.g. older, weakened coniferous forests), the CO₂ backpack is rather low. In a study of more than 230 different scenario comparisons of forest management in Europe and other regions of the world, however, it was found to be positive in all cases, i.e. wood use always leads to a reduction in the CO₂ storage capacity of forests.
How does the CO₂ storage balance influence greenhouse gas balances?
We use wood from the forest for many different purposes: as building material, for furniture, for paper production and as a source of energy. Driven by the goal of greenhouse gas neutrality, forests and wood use play an important role. Harvesting, transport and production of wood products along the process chain release greenhouse gases. Forests absorb CO₂ and supply the renewable raw material wood. If it is harvested and used for the production of wood products, CO₂ stored in the trees is transferred to the products. The more durable such products are, the longer the CO₂ is held back from being emitted. In the case of construction wood, the carbon is stored for decades, but only for a very short time in the case of paper and even shorter in the case of energy wood. In the latter two cases, the CO₂ is soon released again.
Wood products can replace CO₂-intensive materials and energy sources and thus reduce CO₂ emissions. This effect is called substitution. In order to calculate substitution effects, a separate GHG balance must be calculated for the substituted substances and energy sources and compared to the emissions of the wood product. Depending on the wood product, these can vary greatly along the process chain. In greenhouse gas balances of wood products, also the reduction of the CO₂ sink capacity caused by the extraction of wood from forests needs to be included. The CO₂ storage balance measures this reduction and can be included in the greenhouse gas balance. This changes the CO₂ balance of wood use, especially for direct use as energy wood.
Wood use only makes sense from an atmospheric perspective if the GHG emissions of the wood product are lower than the GHG emissions of substituted CO₂-intensive products or fossil energy sources. According to the Renewable Energy Directive (RED II), energy wood should emit at least 70% less greenhouse gases than fossil fuels. More examples of the application of the CO₂ storage balance can be found here.