Comparison of tree stem diameter variations in beech (Fagus sylvatica L.) in Sorø Denmark and in Scots pine (Pinus sylvestris L.) in Hyytiälä, Finland

Tree stem diameter variations were measured simultaneously in beech (Fagus sylvatica L.) in Sorø, Denmark and in Scots pine (Pinus sylvestris L.) in Hyytiälä, Finland. The variations were detected at two heights on the xylem and the whole stem on both trees. The evapo-transpiration of the forests was measured by eddy-covariance method. The pattern of evapo-transpiration was reflected on the diameter variations in both cases. However, the pattern was clearer in Scots pine than in beech. The amplitude of the variation in beech was 0.02 mm in the case of xylem and 0.03 mm in the case of whole stem measurements. In Scots pine the amplitude of xylem diameter variation was 0.05–0.09 mm depending on the measurement height on the xylem and 0.15 mm on the whole stem. The difference in the elasticity of the wood of the two species was reflected in the amplitudes of the variations. The environmental conditions during the measurement period and the measurement methods were similar at both sites, which made the simple comparison possible.