Wood anatomical changes in roots of European ash (Fraxinus excelsior L.) after exposure

Global changes have distinct influence on fluvial processes in torrents causing erosion on slopes and riverbanks even in forested areas. Continuous as well as discontinuous erosion of riverbanks covered by trees frequently results in destabilisation and finally cause the trees affected to tip over. These uprooted trees may lead to a blockage of the river and, in the case of a collapse of the resulting dam, resulting in severe flooding or even debris-flow surges. Dating the time of root exposure along riverbanks allows the reconstruction of erosion dynamics. In the previous studies, roots of coniferous trees have shown anatomical changes (cell size reduction in earlywood) after exposure. This anatomical feature in the xylem of exposed roots has helped to determine the time of exposure at an annual resolution. In the current study, this methodology is now applied for the first time to European ash (Fraxinus excelsior L.) to determine its specific reactions to root exposure.

First results show different reactions in vessel and fibre dimensions. Fibres show a distinct decrease in lumen area due to exposure, whereas vessel lumen area displays more variability ranging from 50% size reduction to no changes. It is discussed that vessel size characteristics are also related to ecophysiological and climatic patterns.