Gully erosion dating by means of anatomical changes in exposed roots (Proboszczowicka Plateau, southern Poland)

Abstract

Re-incision occurs in gullies in the undulating loess plateau in southern Poland. The gully hillslopes are mainly covered with beech trees. The beech roots are exposed in the gullies through erosion. The wood cells in the root tree rings divide into early wood and late wood, and after the roots are exposed, they start to make fewer cells. Dolomites and limestones lying under the loess cover are transported and wound the tree roots. As a result of this process on the border between exposed and unexposed tree rings in the tree roots, scars sometimes occur. These anatomical changes in root tree rings allow to date erosion episodes with one year accuracy. Dating of the exposure of roots indicates that intensive gully erosion in the studied gully started in the 1970s. Since that time, numerous extreme rainfall events responsible for initiating erosion have also occurred. The bottom of the valley head eroded during extreme rainfall events in 1984 and 1991. Erosion here alternates with deposition, its rate being relatively small. Incisions in hillslopes retreated during the flood in 1997, but they originated during earlier rainfall episodes. Hillslope undercutting occurring in the lower part of the gully was formed during older erosion episodes in 1971 and 1984.