Landslides - Extreme Events: A Physical Reconstruction and Risk Assessment - page 188

Figure 7.4. Tree stem bend due to a landslide (from Lang et al. , 1999 ).
competition with other plants. There is also a lack of knowledge on variations
related to substrate characteristics such as smoothness, lithology and degree
of weathering. This lack of knowledge has limited the widespread and com-
mon use of lichenometry. It is important, therefore, that new calibrations of
lichen growth are determined for each study site. Lichenometric dating is usu-
ally restricted to the past 500 years.
Tree-ring dating (dendrochronology)
Trees can record landslide events in two main ways -- tree rings and stem
tilting or distortions. Trees are subjected to stress during mass movements and
this is recorded as a strong and sudden decrease in ring growth. Mass movements
are also registered by tilting of the stem or an S-shaped stem (Fantucci and
Sorriso-Valvo, 1999)(Fig.7. 4 ).
Tree rings are one of the most accurate methods for dating past landslide
events (Fig. 7. 5 ). The year of the event can be estimated and sometimes also the
season. If cross dating of the samples cannot be conducted, age estimates for the