Comparison of spatio-temporal extension of reaction wood and tree-ring eccentricity in juvenile Larix decidua (Mill.) and Picea abies (L.) Karst. trees

Dendrogeomorphology allows for annual dating of various hazardous geomorphic processes in afforested areas. However, there is a lack of detailed knowledge about spatial extent of dated growth disturbances in the whole stems, which is a crucial factor for the selection of an appropriate sampling strategy. In this study, growth disturbances were analysed in the stems of five juvenile Norway spruces (Picea abies (L.) Karst.) and five juvenile Common larches (Larix decidua Mill.) growing on a slope affected by mass-movements. The analysed growth disturbances were: i) reaction wood and ii) tree-ring eccentricity. The relationships between stem curvature and properties of the growth disturbances were studied to offer potential recommendations for sampling. It was found that reaction wood was consistently present at all stem heights in the given event tree ring. Angle extent of the reaction wood tended to decrease with successive tree rings, although an increase in angle extent was observed at higher stem heights (in the case of P. abies). Main direction of the reaction wood tended to be deviated mostly in a near-tilt direction. The properties of the reaction wood had weak associations with both tree-ring eccentricity and stem curvature. Overall, both tree species exhibited similar values of tree-ring eccentricity. Greater eccentricity values appeared mostly in the tilt sampling direction and one of two lateral sampling directions. There was not apparent pattern in the tree-ring eccentricity values observed at different stem heights. Overall, eccentricity had weak influence on stem curvature. To sum it all, both juvenile P. abies and L. decidua trees are good recorders of the two growth disturbances tested. However, differences in the sensitivity of trees to recording events in their annual ring series should be taken into account to achieve the greatest dating potential.