Factors affecting dating quality of scarred Picea abies roots: Implications for dendrogeomorphic reconstructions

Abstract

Exposed and scarred tree roots are valuable environmental archives of geomorphic activity, often used in dendrogeomorphic reconstructions of gully and sheet erosion, debris flood activity, or landslide development. However, their reliability for dating is generally lower compared to tree-ring records in stems. This study aims to evaluate growth anomalies, particularly wedging and missing rings, in Norway spruce roots (Picea abies (L.) Karst.) affected by hydrogeomorphic activity. The objective was to determine whether specific root parameters, such as age, size, shape, or external disturbances, influence the abundance of wedging and potentially missing rings, thereby compromising dating quality. Two datasets of root cross-sections were analysed: (a) 53 cross-sections from eleven roots for multiscale dendrochronological cross-dating and analysis of missing and wedging rings, and (b) 276 cross-sections from 276 individual trees to examine the relationships between wedging ring frequency and root parameters. The results indicate that an increased abundance of wedging and missing rings is mainly associated with decreased annual root area increments and multiple scarring, and is less certainly detectable from increased irregularity in root shape changing from circular to elliptical. Additional analyses also revealed a significantly higher frequency of wedging rings before the first scarring compared to ring sequences after the first scar. To avoid dating errors caused by growth anomalies, future sampling strategies should prioritize thicker roots, which are more likely to have greater root area increments, over smaller roots with a higher probability of extremely narrow rings. Regardless of root age, size, or shape, cutting multiple cross-sections from single roots is strongly recommended to minimize the risk of missing rings.