Application of ash (Fraxinus excelsior L.) roots to determine erosion rates in mountain torrents.

摘要

Due to the effect of global change, the potential risk of natural hazards occurring in alpine areas is expected to increase to an even higher risk-level than has been recorded during the last century. These global changes potentially also have distinct influences on fluvial processes in torrents causing erosion on slopes and riverbanks in forested areas. Dating the time of root exposure along riverbanks combined with common dendrogeomorphic analysis applied to tree trunks helps to reconstruct the erosion dynamics leading to a potential destabilization of adjoining trees. The advantage of using exposed roots compared to common erosion measurement techniques is that the erosion rates can be quantified with annual resolution. The first year of exposure can be determined precisely by the characterization of the wood anatomical changes in the microscopic structure of the root. This study is the first to concentrate on the analysis of wood anatomical features of exposed roots of angiosperm trees aiming to reconstruct erosional processes. Two mountain torrents were selected as study sites based on a preliminary evaluation of various Swiss alpine areas. Sites of special interest concerning erosive processes were classified and examined in five different geomorphological groups representing different processes. The analysis comprised the examination of the exposed tree roots in each group. The project shows the potential of roots in general and in particular roots of deciduous angiosperm trees for geomorphological research, especially concerning erosion studies.