Val av tidpunkt för markberedning vid naturlig föryngring under skärm av Pinus sylvestris i Svealand

Abstract: This thesis is built on a field study that was carried out in two seed-tree stands near by Götbrunna in Uppland, Sweden. The aim was to examine if scarification carried out in spring time could generate a more dense seedling establishment when using natural generation, than scarification carried out in autumn. It was also investigated whether there were differences in mortality the first season between the two plot-types. Plots were established block-wise with 50 blocks (pairs) on each site. The spring scarification was made with a hoe during 22-23 of April. The shelterwood densities were 120-130 stems ha-1 and the seedfalls were registered by five seed-traps in each stand. The seedfalls started in April and were completed in early June. The most intensive seedfall occured during the first half of May. There were large differences in registered seedfall amounts between the two stands, which most likely could be explained by differences in tree-crown sizes and influence from wind. Scarification in autumn clearly affected seed germination and establishment positively, probably due to many factors. The spring plots were not exposed to as many seeds as the autumn plots as a consequence of that the scarification was carried out after the seedfall had started. The autumn plots could during dry periods offer a better water uptake due to a higher degree of compactation. The germination and seedling establishment were significantly improved in exposed mineral soil compared to humus and the amount of exposed mineral soil was 8-10 percentage units higher in the autumn plots than in spring plots. The frequency of plots without seedlings (0-plots) were 38 and 44 %, respectively. There was no significant difference in mortality between the plot-types. In total 6 seedlings died during the first season. According to this study, scarification in autumn is to be prefered compared to scarification in the following spring. Except from the lower degree of seedling establishment, ground frost and snow can delay scarification in the spring, which leads to that a significant part of the seedfall gets unutilized.