We present object protection forest maps for rockfall, shallow landslides and snow avalanches, which were generated within the Interreg Alpine Space project GreenRisk4ALPs with the runout model Flow-py. Six Alpine regions with varying sizes from 45 km2 to 2250 km2, and topographies, from steep valleys of Val Ferret in Italy to the German Alpine foothills in Oberammergau, were modeled. The term direct object protection forest is used for forests that protect objects in developed areas against gravitational natural hazards. That is, a direct object protection forest can only be assigned, if an object is endangered and a direct link between the precise locations of the hazard process area and the object can be established. The two main protective effects forests can have against gravitational natural hazards are 1) to reduce the release probability, or 2) to reduce the magnitude of an event, the effectiveness of both is dependent on forest structure. In addition, the degree to which the forest reduces the energy (magnitude) of the hazard also depends on the speed of the mass. If the magnitude/speed of a hazard process is too high, the forest will be destroyed. The location of a forest therefore determines its protective effect in two ways. First, high elevations and steep terrain (over 45°) will produce a weaker structure and be less effective against gravitational natural hazards compared to lower elevation gentle sloped terrain. Second, the energy of the hazard will be lower closer to the hazard’s release and runout areas than in the middle of the process path.
