Topography, soil carbon-nitrogen ratio and vegetation in boreal coniferous forests at the landscape level

Abstract: This thesis was developed with the main objective of assessing the mutual influence of three of the main factors taking part in the ecological processes of the boreal forest: topography and the hydrological fluxes related to it, C/N ratio in the forest soil, and vegetation composition. The interaction between these factors has not been the main focus in any study of this kind before, although in numerous reports these variables and their role in the forests have been assessed. The project was based on the fieldwork carried out in Ovanmyra, a private forested area located a few kilometres north of Rättvik (Dalarna). Soil samples were taken both from the humus layer and mineral soil, in order to analyze their concentrations of C and N. Topography was evaluated through the Topographic Wetness Index (Beven & Kirkby, 1979), which was calculated from a 5 m digital elevation model derived from airborne laser scanning (LIDAR), and vegetation data was obtained from a digital forest database. Finally, other soil properties, such as pH or stoniness were measured in the field to study their relation with the main variables. Laboratory analyses provided information on concentrations and water content. These data were later studied using several statistical tools, such as descriptive statistics and a principal component analysis. The main results showed that positive correlations were found between soil moisture (through the TWI) and C/N ratio, as well as the vegetation (through forest volume) and C/N in the organic layer. Also in the organic horizon, C concentration is positively correlated to some soil attributes, such as depth of the E horizon and humus thickness. As for the negative correlations, the stand volume proved to be higher when moisture in the soil was lower. Stoniness and C/N ratio were negatively correlated, as were pH and the C/N ratio. Some of the relations explained above were weak enough to require further studies in order to achieve definite conclusions, although most of them were considered strong enough to be representative of the mutual relations measured.