| Forests constitute a major part of terrestrial ecosystems in the world and house a large part of the Earth’s biodiversity. 70% of Sweden’s terrestrial area is covered by forests and almost all the forests can be defined as managed. The most common forestry practice in Sweden is clear-cutting, which consists on the removal of all trees form a specific area, irrespective of size and species. This method results in simplified forest structures and even-aged stands with short rotation times, which have negative impacts on biodiversity and ecosystem functions. Clear-cutting is considered the main cause of fungal species risk and red listing in Sweden. Retention forestry is a practice that aims to mitigate the negative impacts of harvesting by leaving trees at the time of harvest, this is expected to conserve forest biodiversity and ecological functions. A particular method of retention forestry is seed tree retention, in which a set of carefully chosen trees are left over the area to be harvested, these trees will serve as seed source for the new crop of regeneration and in some cases can also serve as a source of timber during future cuttings.
Swedish forests are dominated by Scots pine and Norway spruce, both of which live in symbiotic associations with ectomycorrhizal (ECM) fungi. These fungi serve key functions in forest ecosystems as they provide water and nutrients to their host trees in exchange of carbon. As ECM fungi directly depend on their hosts to obtain carbon, when the trees are harvested the sugar supply stops, which can lead to a reduction of ECM fungal species richness and a shift in the overall soil fungal community composition in the forests. We currently lack a clear understanding on how forestry practices affect ECM fungi at a population level and whether genetic diversity of ECM fungal populations is being directly affected. This knowledge is necessary because loss of genetic variation of ECM fungal populations due to habitat fragmentation can have significant long-term evolutionary consequences, which can alter the functioning of forest ecosystems. Furthermore, it is of immediate relevance if genetic changes directly affect individual fitness and the short-term viability of remnant populations.
This project aims to provide knowledge on how clear-cutting and seed tree regeneration affect the population structure and differentiation of ECM fungi. It will specifically address questions on how these practices affect the genet size, spatial distribution, population structure and genetic diversity of Suillus variegatus, a species that forms ECM associations with two-needle Pinus species, and that is the dominant bolete in Scandinavian Scots pine mature forests. In this project, we will sample and whole genome sequence populations of S. variegatus in forest stands of Scots pines that have been managed by two different forestry practices, clear-cut and seed tree retention, in addition to old growth forest, in order to compare the population structure of this ECM fungus. These results will be relevant for Swedish nature conservation, as it will provide scientific evidence to inform forest management decisions, in particular to inform which harvesting method is better for the overall conservation of the forests.
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