How does thinning affect forest carbon? A look at an upland and a drained peatland forest
Thinning, the practice of removing some trees to help others grow better, changes how much carbon a forest stores or releases. We studied this effect in two forest types: an upland forest on mineral soil, and a peatland forest drained for forestry many years ago. We measured carbon storage and emissions in trees, forest floor plants, soil, and deadwood, both before and after thinning.
We found that thinning caused an immediate drop in annual carbon accumulation, especially in tree biomass, as many trees were removed. But within a year, the forest began to recover. Thinning also contributed to increased carbon emissions due to higher carbon release from decomposition of harvest residues.
In the upland forest, recovery was relatively fast. Forest floor plants like mosses and shrubs took advantage of the extra light and space, helping to absorb more carbon. One year after thinning, this site went from a temporary carbon-emitting source to a carbon sink again.
In the peatland forest, which was already a carbon source before thinning, tree removal intensified carbon emissions. Even one year after thinning, the forest continued to release more carbon than it absorbed. This was due to slow tree growth combined with ongoing emissions from the soil and leftover harvest residues such as branches and stumps.
This is important because thinning affects more than just the trees; it alters the entire carbon balance of the forest ecosystem. In upland forests, carbon storage can recover within a few years. However, in drained peatlands, recovery may be slower, and these forests might continue to release carbon for some time after thinning. This study is a case study of two forests, and additional research, particularly in drained peatlands, is needed to better understand the broader impacts of thinning. As Finland and other countries pursue their climate goals, it is essential to understand how different forest types respond to management practices. Sustainable forestry must balance timber production with maintaining forests as effective carbon sinks, especially in sensitive ecosystems such as drained peatlands.
For a detailed discussion of methods and findings, see the original study by de Quesada et al. (2025).
This article was written by Gonzalo de Quesada (University of Helsinki).
More information:
de Quesada, G., Rautakoski, H., Xu, J., Li, Q., Larmola, T., Salovaara, P., Anttila, V., Peltoniemi, M., Koskinen, M., Lohila, A., Aalto, J., Lehtonen, L., Bäck, J., Mäkipää, R., Heinonsalo, J., Salmon, Y., & Lintunen, A. (2025). Carbon dynamics after thinning in two boreal forest sites: Upland and drained peatland. Forest Ecology and Management, 595, 123024. https://doi.org/10.1016/j.foreco.2025.123024
