Geophysics-based landslide zonation explains spatial variability in tree-ring growth disturbances

Complex landslides contain internally heterogeneous zones that may respond differently to reactivation, complicating tree-ring based chronologies of slope activity. This study combines dendrogeomorphological analysis with electrical resistivity tomography (ERT) to test whether geophysics-based zonation could explain the spatial variability of tree-ring disturbances within a large complex landslide. ERT profiles and geomorphological mapping delineated three mechanically distinct zones: a downslope shallow-landslide sector (S zone), a moisture-rich gap infilled by weakly consolidated material (G zone), and an adjacent compact block with tension cracks (B zone). In total, 200 Norway spruce (Picea abies (L.) H. Karst) were analysed for reaction wood (RW) and abrupt growth suppression (GS). RW intensity was quantified for each affected ring and GS classified by relative ring-width reduction.

RW clearly dominates across the landslide. The S zone shows the highest stem inclinations and RW intensities, indicating enhanced shallow deformation, whereas RW duration is similar among zones. GS occurs everywhere but is proportionally most frequent in the B zone. Correlation analyses show that in the S and G zones, RW intensity and duration relate significantly to stem inclination, while no significant relationships appear in the B zone.

These results demonstrate that internal landslide heterogeneity, as delineate by ERT, is reflected in tree-ring responses. Geophysics-based zonation offers an effective framework for interpreting growth disturbances and improves dendrogeomorphic reconstructions of complex slope movements.