Anders Ahlström

I study Earths great cycle of carbon and its interplay with climate and management, and I currently invest much of my time on the study of primary forests.

In 2018 colleagues and I 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.