Soil and vegetation factors affecting carbon storage in a coastal forest in NE Germany

A large part of carbon in forest ecosystems is stored in the soil. Large-scale inventories of soil C stocks in European forests have been published. Nevertheless, detailed site-specific studies are still necessary, because C storage is spatially highly variable and depends on site specific soil, ecological and management factors, which cannot be captured by large scale studies. Here, we assess C stocks in a coastal forest at the Baltic Sea with different tree species, stand ages, management, and soils, to elucidate possible causes for differences in carbon storage. Soil samples were taken down to 1 m depth both from soil profile pits with 250 cm(3) cores and by auger cores in the years 2017-2019 in forest treatment plots which varied with respect to forest management, tree species (beech, birch, oak), and tree age. Although the abiotic parameters soil type (mainly gleysol and podsol), soil texture (mainly sandy), pH value, groundwater depth and distance to the coast were not part of the treatment design, these factors were - along with the biotic factors - evaluated to foster our understanding of the importance of possible drivers of carbon storage in forests. Soil carbon stocks were evaluated for 0-1 m soil depth using measured C concentrations in the soil samples and bulk densities. Carbon stocks in the vegetation were determined by detailed stand inventories of the trees on the forest plots. Total ecosystem carbon stocks were on average 50 kg C m(-2), i.e., about threefold higher than the reported average values for forest ecosystems worldwide in temperate climates. Soil C stocks were on average 32 kg C m(-2) (0-1 m depth). This is distinctly higher than soil C stocks reported for most other forest sites in similar climatic conditions, and is likely caused by widespread occurrence of anaerobic conditions in the soil, but also by high bioproductivity due to good water availability and low drought stress. Variability of soil carbon stocks at this site is predominantly governed by soil factors (soil type, soil texture, soil pH), whereas tree carbon stocks are mainly determined by tree species and tree age.