The effect of gap openings on soil reinforcement in two conifer stands in northern Italy

•Old conifer stands showed a low probability of slope instability also at saturation.•After 2–3years from felling the probability of slope failure exceeded 50%.•After 5years from felling slopes was intrinsically unstable for saturation >75%.•Natural regeneration process was slower than root decay.•Gap-cutting practice must adapt gap size and shape to instability concerns.