Jennie Sandström at Mittuniversitetet in Sundsvall has been doing research for several years. In her laboratory are tree samples from 200 trees that come from one of her completed projects.
It was about looking for traces of historic fires in the future nature reserve Horten, on the border between Västernorrland and Jämtland counties. The data was then used as a basis for forest management plans in the area. See the tree sample and hear why the mystery seems to remain unsolved.