The forest ecosystem is a significant climate-influencing factor, especially when it comes to greenhouse gas emissions. The essence of this climate-influencing mechanism lies in the ability of trees to absorb atmospheric carbon dioxide through photosynthesis and store the carbon contained in CO2 within their trunks, branches, and root systems throughout their lifespan. Carbon absorbed by a growing tree through photosynthesis is effectively 'removed' from circulation and no longer contributes to the formation of climate-damaging greenhouse gases.
117 overmature forest stands studied
To increase carbon stocks in forests, knowledge is required regarding how much carbon is stored by stands at different ages, as well as an understanding of the factors that influence this accumulation. Until now, there was insufficient information on carbon stocks in old-growth stands, the area of which is increasing in both Latvia and Europe as a whole. To find answers, the Latvian State Forest Research Institute 'Silava', commissioned by JSC 'Latvijas valsts meži', conducted a study between 2016 and 2020 titled 'Assessment of greenhouse gas emissions and CO2 sequestration in old forest stands'. The goal of the study was to evaluate carbon stocks in old or overmature pine, spruce, birch, and aspen stands that have not been affected by economic activity for a long period, in comparison with mature and ripening stands.
A total of 117 overmature forest stands were measured and analysed. The study provided data on carbon stocks in overmature deciduous stands that are unique on a European scale and significantly expanded knowledge regarding stocks in overmature coniferous stands. The information obtained will be a significant support when assessing the impact of various strategic and political decisions on the total carbon stock of forest ecosystems.
Carbon accumulation decreases with stand age
The results of the study show that living tree biomass, which is the largest carbon reservoir, makes up half of the total ecosystem carbon stock in both overmature (47-59%) and mature (46-54%) stands. After the transition from the mature to the overmature stand stage, which averaged 93 years for conifers and 58 years for deciduous trees, carbon sequestration in the forest stands continues. The largest additional carbon storage (on average 61% of total growth in coniferous stands and 82% in deciduous stands) during this period is provided by the increase in living tree biomass, which occurs as the trees continue to grow. Although carbon accumulation continues in overmature forest stands, the study results showed that the annual carbon accumulation in living tree biomass and deadwood in overmature stands is significantly lower than in mature and ripening stands; furthermore, it decreases as the age of these stands increases, even when trees of the respective species and age remain the dominant forest element.
Ripening stands store the most carbon
Although old forest stands without forest management continue to store carbon, preserving them after they have reached mature stand age does not ensure efficient use of land resources for maximising carbon sequestration. To optimise carbon storage, it is important to ensure high stand productivity. The study results indicate that ripening stands have the highest annual carbon accumulation in both living tree biomass and deadwood. This means that by increasing the production of wood products in ripening-age forests, a greater amount of carbon would be sequestered and stored long-term in wood products, which in turn would reduce the negative impact of CO2 on the climate.