Mapping primary forests in Sweden

In 2018 we started mapping primary forests in Sweden with aim to provide a basis for our network of forest plots and satellite-based analysis. To date more than 500 forests have been added to our digital map making it one of the most extensive maps in Europe.

Primary forests have many definitions and several related terms exist, such as pristine or virgin forests. They are sometimes also referred to as old-growth forests. In reality there is a continuum of naturalness defined by the amount of past human impacts. We have therefore ranked all forests by naturalness and our map includes forests ranging from old-growth that may have experienced some selective logging and forest grazing to primary forests with no signs of direct human impact.

Primary forests are rare in Sweden, the mapped forests represent only 2% of Sweden’s forest land, and only a portion of this 2% are primary forests of the highest naturalness. They are, however, highly valuable for research. They inform us on how ecosystems would have looked without direct human impact, and they can therefore be seen as a part in a long-standing experiment, where they act as a control or baseline to an experiment of land use that may have been ongoing for centuries. In this way they form an experimental setup that no researcher could create in a life-time.

Film from our field work in 2021

Forest plot network

One of the main motivations for mapping the primary forests was to be able to establish a network of forest inventory plots that target the most natural forests below the mountain foothills, that is, forests that are otherwise representative for the general landscape.

We started establishing plots in 2019 and our network now includes plots in more than 30 forests. The network includes forests across the country, from the arctic circle in the north to the southern temperate zone.

Our main research questions include carbon storage, changes in carbon storage (i.e. uptake or release of carbon), vegetation structure, vegetation composition and biodiversity. We are also increasingly using the network for understanding how climate change has impacted our natural ecosystems with several initiated and planned sub-projects.

Publications

Wolf, J., Asch, J., Tian, F., Georgiou, K., & Ahlström, A. Canopy responses of Swedish primary and secondary forests to the 2018 drought. Environmental Research Letters, 10.1088/1748-9326/acd6a8. 2023. Link to paper

Mikolāš, M., Piovesan, G., Ahlström, A., Donato, D.C., Gloor, R., Hofmeister, J., Keeton, W.S., Muys, B., Sabatini, F.M., Svoboda, M., Kuemmerle, T. Protect old-growth forests in Europe now. Science, 10.1126/science.adh2303, 2023. Link to paper

Ahlström, A., Canadell, J.G., Metcalfe, D.B. Widespread Unquantified Conversion of Old Boreal Forests to Plantations. Earth's Future,  10.1029/2022EF003221. 2022. Link to paper

Ahlström, A., de Jong, G.E., Nijland, W. & Tagesson, T. Primary productivity of managed and pristine forests in Sweden. Environmental Research Letters, 10.1088/1748-9326/ab9a6b, 2020. Link to paper