Kirjanpainajatuhon vaikutus pintamaan hiileen Lahden taajamametsissä

Forests are important carbon pools for combating climate change. Forest disturbances, such as insect outbreaks, can temporarily change a forest and forest soil to a source of carbon. Tree mortality reduces forest carbon uptake and increases emissions from the decay of killed trees. Climate change is expected to impact the susceptibility of forests to disturbances. For example, the number of insects in forests is predicted to increase and therefore the impact of pests on forest ecosystems will also increase. This can weaken forests carbon sequestration. The purpose of this master's thesis was to study the effect of the European spruce bark beetle (Ips typographus L.) on the carbon in the surface layers (humus and the mineral layer of depth 0‒5 cm) of the soil. In this study, the aim was to study the effect of tree mortality and tree damage intensity caused by the spruce bark beetle on the forest topsoil carbon stock. In addition, changes in the carbon content and C / N ratio of soil surface layers were studied. The aim was also to study the effect of stand- and tree-wise characteristics on the carbon content of the topsoil. The field work was carried out in urban forest area, in Lahti,Southern Finland. In years 2012–2013 stand- and tree-wise characteristics were measured on 49 plots. The spruce bark beetle-induced symptoms and forest site classification were also estimated. Further, three soil samples were taken from each plot for carbon analysis from the humus layer and 0‒5 cm depth of mineral soil. Proportion of carbon (C %) and C/N ratio were analysed from the samples and the amount of carbon (kg C m-2) was determined. The amount of carbon in the experimental area was on average 0.6 kg C m-2 and varied between plots 0.1 and 1.5 kg C m-2. The amount of carbon varied statistically significantly between forest types. At a more herb-rich forest types (OMT/OMaT-groups= more rich forest types), the soil carbon content was significantly higher than in MT-type. Also, the C / N ratio and C % were both significantly higher in the humus layer than in the mineral soil. In this study, the dead spruce trees (%), dead spruces diameter (d1,3) or basal area of dead spruce trees did not increase the amount of carbon in the surface layers of the soil. Also, the tree damage intensity caused by the spruce bark beetle did not explain the amount of carbon (kg C m-2), proportion (C%) or the C / N ratio of the soil surface layers. However, there was a correlation between the stand- and tree-wise characteristics and the carbon content of the soil in more rich vegetation/forest site (OMT/OMaT): The proportion of spruces showed a relationship with C % and C/N-ratio, and basal area of spruces with carbon content of the soil (kg C m-2). This study did not find a relationship between spruce bark beetle and surface layers of soil carbon. This may be due to the fact, that the time frame of this study was too short to observe any changes. In addition, this study did not compare fully healthy vs. seriously damaged spruce forests, in which case the difference in soil carbon content would have been observed. Furthermore, this study did not quantify potential changes in litter layer carbon caused by the spruce bark beetle. The following studies may need to be done over a longer period of time, adding control plots to the study, and also the carbon contained in the litter layer. On the other hand, many environmental factors affect to natural processes simultaneously. Therefore, studying a single variable may not necessarily give a true picture of causality in nature.