Regeneration establishment after conversion to multi-layered stands in Jämtland, central Sweden

Abstract: In 2010, different thinning treatments were applied in two Norway spruce (Picea abies) stands of 45 and 46 years in Jämtland, central Sweden. The goal of the main treatment was to achieve a high diameter variation with the long- term goal to develop a multi-layered stand. In some study plots, soil scarification and fertilization measures were carried out to promote early natural regeneration. The purpose of this master thesis was to quantify the very early establishment and development of forest regeneration in both study stands. Five years later, the regeneration was measured again. Data from 2010 and 2015 were used to investigate if there was any difference between the two stands, if sufficient regeneration had occurred and if the different thinning-, fertilization-, and scarification treatments or the forest floor cover had an influence on recruitment, height increment and mortality of naturally regenerated Norway spruce and birch seedlings. The differences in species of seedlings between the two stands were rather large. While more Norway spruces ha-1 regenerated in one stand, the regeneration of birch ha-1 was a lot bigger in the other stand. Regeneration was rather poor, especially the regeneration of Norway spruce in a Norway spruce- dominated forest. In average, there were only about 1600 Norway spruce seedlings ha-1 on the plots which was very little compared to other regeneration studies and taking into account that every Norway spruce on a subplot was counted as a seedling, which included seedling sizes between 2.5 and 99 cm. However, calculating with a general ingrowth ratio, the current regeneration might still provide sufficient ingrowth in the future. The influence of treatments was small five years after the initiation of the experiment. The only significant result was that seedlings had smaller height increment on control plots, while no clear conclusions could be drawn on the mortality or recruitment. If the forest floor was dominated by mosses, the regeneration of both Norway spruce and birch were smaller than expected. Other important factors for the regeneration were probably wet soil and good light conditions for birch and coarse woody debris to germinate on for Norway spruce. In addition to the results presented, the value of this study is the documentation of the initiation and very early regeneration development of this experiment.