Response of anatomical structures in tree roots to an erosion event on the southeastern Tibetan Plateau

Exposed roots have been used in dendrogeomorphology to determine erosion rates. However, few studies have focused on the changes in ring width and in the anatomical properties of hardwood roots exposed by soil erosion at a macroscopic and microscopic level. In this study, we identified the ring width and the anatomical response of hardwood root to a denudation event and applied these anatomical findings to the reconstruction and quantification of soil erosion rates. A total of 136 cross sections (54 from buried roots and 79 from exposed roots of 25 trees) were sampled in the study area. Measurements of the widths of the growth rings, the average vessel area in earlywood, the average vessel area per ring, and the vessel number per ring were performed with WinDENDRO and ImageJ. Our results show that the analysis of vessel features is a useful tool to identify soil erosion events recorded during the life of a tree. A sharp decrease of nearly 50% in the vessel area of earlywood was an important signature indicating the exposure of tree roots caused by denudation. Soil erosion rates derived from exposed roots varied between 1.04 and 3.61 mm y- 1 in the southeastern Tibetan Plateau.