The role of tree uprooting in the transporting of sediment and mixing of soil in the Tatra Mountains

Abstract

Tree uprooting is an important process which leads to many geomorphic consequences. Some of the most important are the transport of sediment and mixing of soil. The aim of this article is to make a detailed examination of the magnitude of sediment transport caused by an extreme windthrow event in three severely affected catchments. Also, a comparison is made of the windthrow event with a mass movement event in the aspect of the magnitude of sediment transport and soil mixing. The study was conducted in three second- to third-order catchments in the Tatra Mountains, where a strong foehn wind event caused extensive windthrow in 2013, and a high-magnitude rainfall event triggered mass movements in 2007. The volume of sediment uplifted by the uprooting event was calculated based on the mapping of root plates using high-resolution (0.04 m) aerial images and measurements of root plate volumes conducted in the field. The volume of sediment transported by shallow landslides was determined based on a Digital Elevation Model (DEM, 1-m resolution). Windthrows affected 34%, 76%, and 94% of the area of the investigated catchments. Most of the trees had fallen downslope. The direction of treefall was influenced by the slope aspect and steepness. Root plates and pits covered 1.3%, 4.8%, and 5.4% of the area of the catchments. Sediment flux generated by the uprooting event, calculated for the entire area of each investigated catchment ranged from 8.1 × 10−4 to 9.9 × 10−3 m3 m−1 event−1. This was notably lower than the sediment flux generated by the mass movement event (also calculated for the entire area of each catchment), which was 1.8−6.1 × 10−2 m3 m−1 event−1. By contrast, uprooting affected a much larger area than the mass movement event, which underlines its significant role in the mixing of soil.