Tree rings as an early warning against catastrophic landslides: Assessing the potential of dendrochronology for determining slope stability

We investigated three slopes (in southern Poland, the Carpathian Mts, and the Sudeten Mts) subject to catastrophic, sudden landslides. To reconstruct past landslide activity, we analysed the eccentricity of tree rings in the stems of Norway spruce (Picea abies) using a per cent eccentricity index method. We obtained data on year-by-year changes in eccentricity patterns of single specimens, as well as data on landslide events dated from the whole population of trees sampled on each slope (13–30 spruce trees). These data supplied indirect information on the temporal variability of landslide activity on the three slopes revealing that all three slopes were subject to frequent landslide activity (recurrence intervals 2.0–2.7 years) well before catastrophic events that occurred in 1997 and 2010. The study also showed that 3–5 years before a catastrophic event the sample trees started to record increasing ground instability demonstrated as an uninterrupted, sudden increase in the eccentricity of single trees. Our results suggest that the application of dendrochronological methods can reveal slopes at an increased risk of catastrophic landsliding well in advance. The methods we applied show great promise for forecasting catastrophic landslides and assessing landslide hazard, slope stability and the effectiveness of engineering works undertaken to stabilise landslides.