Vegetation evolution by ecological succession as a potential bioindicator of landslides relative age in Southwestern Mediterranean region

Landslides have a direct impact in the ecosystems dynamics being considered one of the main vegetation perturbation processes. Our objective is to determine the relation between vegetation cover evolution and time period after landslide disturbance, and therefore to assess the potential use of vegetation evolution within landslide areas as temporal bioindicators of landslide activity, in order to determine landslide relative age. Four rotational slides of known relative age, located in the Grande da Pipa River basin (Arruda dos Vinhos, Portugal) were selected. The methodology includes four main steps: (1) to identify the flora and vegetation differences between the main landslide sectors (scarp, body, foot); (2) to find out if the differences in floristic composition and vegetation structure are reflected in the succession process; (3) to find out if the succession process has produced different seral stages along the longitudinal gradients; (4) to compare the succession process in landslide affected areas with the undisturbed adjacent areas. The data points towards a slow evolution of the vegetation in the period following the disturbance, being necessary long periods for the perturbed area reach vegetation characteristics similar to the ones of the unperturbed areas. The progressive succession is rapid in the foot, slow in the body and extremely slow in the scarp. The presence of orchids in the body may be considered as an age bioindicator of more than 15 years since landslide disturbance. In the case of the older landslide (> 50 years), it corresponds to the evolved stage close to the potential natural vegetation.