Mobile Laser Scanner understory characterization: an exploratory study on hazel grouse in Italian Alps

Forest vegetation structure assessment is a time expensive effort with traditional methods. The Mobile Laser Scanner (MLS) technology can greatly speed up field works, achieve detailed quantification of three-dimensional forest structure at detailed resolution and drive forest management to increase the conservation status of forests-specialist bird species. In this study, using Mobile hand-held Laser Scanner (MLS), we calculated a fine-scale vegetation density index (namely the Plant Density Index, PDI) to characterize the vertical structure of forest subcanopy (0-10 m). The collected MLS point clouds were used to estimate the abundance of Potential Hiding Refuges (PHR) for the hazel grouse (Tetrastes bonasia), a sedentary bird extremely sensitive to forest structure and composition. The study was carried out in 10 plots located in the Adamello Brenta Geopark (Southern Alps, Italy). The species was detected in 8 out of 18 transects in an uneven-aged spruce forest with a discontinuous tree cover. The PDI decreases as the height increases, showing greater value in the shrub and herbaceous layer while the upper values are represented by trees stems, and branches. Visibility analysis of lower understory, highlighted PHR mean value of 73.2% (sd = 9.2%). In our area, PDI and PHR revealed that the environmental factors for hazel grouse occurrence are forests with open habitats, understory vegetation, and good hiding opportunities. Our study is the first application that uses MLS derived parameters to describe the ecological niche of a grouse and we presented the surveyed area as "case report" of hazel grouse habitat.