François Lehaire

Canopy Gap Mapping from Airborne Laser Scanning: An Assessment of the Positional and Geometrical Accuracy

Canopy gaps are small-scale openings in forest canopies which offer suitable micro-climatic conditions for tree regeneration. Field mapping of gaps is complex and time-consuming. Several studies have used Canopy Height Models (CHM) derived from airborne laser scanning (ALS) to delineate gaps but limited accuracy assessment has been carried out, especially regarding the gap geometry. In this study, we investigate three mapping methods based on raster layers produced from ALS leaf-off and leaf-on datasets: thresholding, per-pixel and per-object supervised classifications with Random Forest. In addition to the CHM, other metrics related to the canopy porosity are tested. The gap detection is good, with a global accuracy up to 82% and consumer’s accuracy often exceeding 90%. The Geometric Accuracy (GAc) was analyzed with the gap area, main orientation, gap shape-complexity index and a quantitative assessment index of the matching with reference gaps polygons. The GAc assessment shows difficulties in identifying a method which properly delineates gaps. The performance of CHM-based thresholding was exceeded by that of other methods, especially thresholding of canopy porosity rasters and the per-pixel supervised classification. Beyond assessing the methods performance, we argue the critical need for future ALS-based gap studies to consider the geometric accuracy of results.

Is wild boar heading towards movement ecology? A review of trends and gaps

Studies about the movement of mammals have recently gained much emphasis thanks to the development of new tracking technology, allowing highly accurate recording of animal movement. However, the amount of data made available requires effective theoretical and analytical framework for appropriate scientific use, i.e. to answer questions of interest. Within this review, we used systematic reviewing technique and the movement ecology framework to assess current knowledge and gaps in wild boar Sus scrofa spatial behaviour, species of high economic, ecological and social interest. Specifically, we observed that the development of new tracking techniques (radio-telemetry and global positioning system) has promoted movement-related studies since the early 2000. However, the ecology of movement, i.e. the why, how, when and where exactly an individual is moving is rarely the focus of these studies, which instead lies in the consequences of wild boar movement, e.g. the spread of disease, seed dispersal or damage. Most of the current studies are thus concerned with the interaction between environmental factors and spatial behaviour of the species, while other components of movement, internal state, navigation, and motion capacity are seldom studied. Compared to others ungulates, we also observed that wild boar movement ecology is still poorly considered in the literature. This review highlights the need for more quantitative descriptions of movement and behavioural-based approaches relating wild boar movement to its internal, navigational, and motion capacities. We expect that facilitated access to tracking technologies, in terms of cost and miniaturization, along with current interest in movement ecology will greatly promote increased knowledge in wild boar spatial behaviour.