Airborne LiDAR Mapping for Vegetation Analysis

Airborne LiDAR data were collected by the National Centre for Airborne Laser Mapping (NCALM) in May 2011 (S1 File). Persistent cloudiness over some parts of the mountains prevented reaching a point cloud density sufficient to reliably identify ground returns [13 ]. This affect only 3% of the study area, however, and that part was patched with a 10 m-resolution DEM. The 1 m-resolution LiDAR DEM was resampled at 5 m to reduce noise resulting from the inability of algorithms to tease out the scattering resulting from the low density of ground returns from the scattering produced by the presence of large corestones at the bottom of many coves (S1 Grid 1 in S1 File). The 5m-resolution DEM was used to calculate topographic metrics that capture some of the topographic characteristics that affect the distribution of vegetation: elevation, aspect, slope steepness, and depth between two consecutive ridgetops (hereafter referred to as entrenchment depth). This later parameter was obtained by passing a surface envelope through the hilltops, and then subtracting the 5m-resolution DEM from this envelope (S1, S1 Grid 2 in S1 File).