Overstory dynamics as an indicator of ecosystem services from the understory vegetation in coniferous forests in Sweden

Sammanfattning: Understory vegetation is a wide and diverse part of the forest environment, which provides a lot of information about the forest, its condition and ecosystem services. Understory vegetation is affected and moulded by the species composition and density of the overstory, which changes growth conditions and productivity in the lower layers during the whole rotation period. National Forest Inventories (NFI) supply long term time series of forest conditions. Recently NFIs also widened the scope to include other ecosystem variables, e.g. different biodiversity components, carbon sequestration and deadwood occurrence. Hence, there is a great opportunity, with data from this source, to analyse the correlation between understory and overstory vegetation, and make inferences on the relationship between these selected features and their influence on ecosystem services. The aim of this thesis is to study understory ecosystem services in coniferous stands in the boreal and hemi-boreal regions of Sweden by analysing correlations between understory and overstory vegetation. The data for this study was acquired from the Swedish NFI. Interest of this research is narrowed to spruce and pine dominated stands, which are selected from among thousands of available study plots in the NFI database. The plots are sorted depending on dominant tree species and age into species specific chronosequences. Furthermore there is also a latitude gradient criterion – analyses were performed separately for 5 different region of Sweden. In this study, by analysing almost 16 000 sample plots, the following ecosystem services were researched: 1) supporting ecosystem services (biodiversity based on vascular plant species number in the field-layer and game potential based on vascular plant cover in the field-layer) 2) provisioning ecosystem service (berry production based on bilberry and cowberry cover) There are several significant differences in occurrence of the studied ecosystem services depending on the overstory. Spruce dominated stands have a higher biodiversity than pine stand in most of Sweden (regions 1-4; in all age classes), but the situation inverts in the most southern region (5). The highest game potential occurs in northern Sweden in spruce stands, and in southern Sweden in pine stands. The bilberry production rises proportionally with the age, irrespective of stand type. The highest cowberry production occurs in pine dominated stands, independently of region and age class. Differences between age classes in output of ecosystem services are much smaller in northern Sweden than in the southern part of the country.