Impact of piping on gully development in mid-altitude mountains under a temperate climate: A dendrogeomorphological approach

Gullies are complex geomorphic systems induced and transformed not only by surface erosion processes, but also by subsurface processes such as piping. However, the transient nature of piping makes this process more difficult to observe and study, especially when a pipe roof has totally collapsed. This study aims at assessing piping impact on gully initiation and development using dendrogeomorphological analyses, which are a novel approach in piping study. The survey was carried out in a mountainous area under a temperate climate, using the Bereźnica Wyżna catchment in the Bieszczady Mts. (Eastern Carpathians) as a case study. We estimated the minimum age of pipe collapses and presented the transformation of pipe collapses in order to identify the direction of pipe and gully development. We also verified the contribution of piping to gully development by the reconstruction of gully bottom deepening. The analysis was based on changes in tree and root wood anatomy in diffuse-porous deciduous angiosperm species, i.e. common alder (Alnus glutinosa) and field maple (Acer campestre). The pipe collapses in the piping system studied are at least 19 to 23-27 years old and the pipe roof initially collapsed in the lower sections of the slope (above the gully head) and the pipe develops up the slope by headward erosion. The gully that was analysed in forest had been deepened by piping during several episodes connected with high precipitation events. In contrast, the pipe located in grasslands collapsed 1-2 years after such events indicating that dense vegetation delays pipe collapse. This study shows that dendrogeomorphological analyses based on diffuse-porous deciduous angiosperm species may be a useful tool in piping research. It provides information on pipe and gully development, as well as enabling estimates to be made of the age of pipe collapses.