Assessing Shrub and Tree Encroachment in Alpine Pastures from Airborne Laser Scanning Data

The forest area in alpine regions is increasing. Agricultural land is abandoned; shrub and tree encroachment and reforestation are the consequences, with negative impacts on agriculture, biodiversity and tourism. Assessing encroachment on agricultural land from Airborne Laser Scanning (ALS) data was tested in three study areas in Switzerland. The results of the data evaluation were compared with those for manually collected data from the interpretation of orthophotos. The evaluation indicated that when a higher point density was available, the detection rate for areas with shrub and tree encroachment was also higher. The workflow using the Vertical Complexity Index (VCI) turned out to be robust for both large areas and large datasets. The accuracy levels achieved in this study for the encroachment index may provide a solid basis for prioritizing certain areas for projects that aim to limit the process of reforestation.