Biomass allocation, carbon content change and carbon stock distribution of Scots pine (<i>Pinus sylvestris</i> var. <i> mongholica</i>) plantation forests at different stand ages and densities in the sandy area of western Liaoning Province, China

Scots pine (<i>Pinus sylvestris</i> var. <i>mongholica</i>) is one of the main afforestation species in the southeastern edge of the Horqin Sandy Land, which not only effectively prevents the expansion of the sandland, but also serves as an important carbon reservoir. Uncovering the biomass allocation, carbon content changes and carbon stock distribution among organs of Scots pine at different ages and densities can provide a theoretical basis for rational afforestation and management in the western Liaoning sandy area. In this study, the biomass and carbon content of four organs, namely, trunk, branch, leaf and root, were measured at different age classes (young stage, half-mature stage, near-mature stage, mature stage and over-mature stage forests) and densities, and the carbon stock of Scots pine plantations in the western Liaoning sandy area was estimated. The results showed that the biomass of all organs except leaves increased with the increase of stand age, but the rate of increase of each organ was not consistent. To resist wind and sand, the biomass was preferentially allocated to the trunk and roots, which was in line with the theory of allometry and optimal allocation. The carbon content of each organ of Scots pine increases and then decreases with the rise of forest age classes, and the root carbon content is the lowest in five forest ages, and the plant carbon is mainly stored in the aboveground part. The biomass of each organ in both near mature and mature forests increased with the decrease in density. Still, the root carbon content decreased with the decrease of density, and the PCA analysis showed that near mature and mature forests had better carbon sequestration capacity in low density. The carbon stock of Scots pine plantation forests in the sandy area of western Liaoning was mainly concentrated in Fuxin and Chaoyang cities, and the lowest carbon stock was found in Jinzhou. The age and density of the forest stand are important factors affecting the biomass and carbon content of Scots pine, therefore, when operating Scots pine plantation forests in the sandy areas of western Liaoning, different stand densities should be retained at different age stages, so that their biomass and carbon content can be sufficiently accumulated and distributed to improve the local environment.