Mean root depth estimation at landslide slopes

tPlant rooting systems affect slope stability through the soil reinforcement given by the root network.The vertical root distribution in particular is crucial for the assessment of the critical slip surface in slopestability analyses. We propose here an expeditious way to assess the major characteristics of the rootsystem at landslide slopes.More in detail, we extend and validate an ecohydrological model proposed for flat terrain and water-dependent ecosystems by Laio et al. (2006). This model has the merit to use readily available climaticand pedologic descriptors to predict the mean root depth, but its extension to hillslopes in semi-humidenvironments requires validation. The model has been improved and then tested on a case study innorthern Tuscany (Italy) which considers 17 landslide sites where the tree rooting systems have beenmeasured.The results show a quite good match between observed and modeled mean root depths. The accuracyof the results largely depends on the improvements brought to the model in the parameters estimationphase, in particular through the application of the Curve Number method and through the refinement ofthe definition of the growing season. The results show that in 14 cases out of 17 the error is lower than30%. Furthermore, the error becomes lower than 30% at all sites if we take into account differences amongsoils in the estimation of the portion of precipitation which infiltrates into the soil. These results provethe potential of the proposed method: using few and quite readily available parameters, it allows one todetermine the mean root depths of vegetation with good accuracy: an important parameter for stabilityassessment of vegetated slopes on a large scale