The understorey is an essential compartment of the forest ecosystem as it hosts the young life stages of the trees that will constitute the future canopy. The understorey trees however are less studied than the canopy trees. Environmental heterogeneity occurring at small-spatial scale strongly influences the structure, composition, and functioning of tropical rainforests. Environmental filters particularly influence the establishment and survival of young individuals. The relative importance of different micro-environmental variables in shaping tree species distributions through their habitat preference and their regeneration niche however remains an open question, due to methodological limitations in the characterisation of the small-scale abiotic environment. In this project, we propose to address this knowledge gap and methodological limitation by using the innovative and promising LiDAR technology. LiDAR has already proven its ability to describe the 3D forest structure and topography on a fine scale. Forest structure and topography already allowed the prediction of important micro-climatic components for trees and notably light and associated air temperature and moisture as well as local drainage regime. LiDAR technology may also be able to predict other conditions essential to plant life: soil temperature, water and nutrient access. The LiDAR acquisition methods currently used to map forest structure have some limitations. Airborne laser scanning fails to describe the lower canopy in sufficient detail. Terrestrial laser scanning using fixed scan position below the canopy is limited in terms of its spatial coverage. The recent development of Mobile Laser Scanning (MLS), overcoming these limitations which make it the perfect candidate to assess understorey micro-environment. We therefore propose to describe the structure of the forest understorey with MLS and to compare its effectiveness in predicting micro-environmental variables with other techniques.