Adequate management of forest resources is recognized as a solution to strengthen the action of forests as a carbon sink and mitigate climate change. As forests also play a key role for energy supply and biodiversity conservation, sustainable management of forest ecosystems is critical for the future of mankind. Acquiring consistent and extensive data from space to monitor forest environments is a technological challenge we have to face to increase our knowledge on forest ecosystem functioning and to address the challenge of forest sustainable management. By its ability to measure the vertical structure of land cover, airborne lidar technology is highly qualified for forest applications but developing spaceborne systems remains a challenge that several space agencies are trying to meet. In France, CNES (French space agency) has supported scientific projects with the aim of studying the potential of a vegetation lidar and defining appropriate instrument specifications. The aim of this presentation is to give an overview of some of these studies and their main recent outcomes. These studies include: 1) the development and the validation of a platform to simulate Lidar signal on forest environment, 2) the use of the platform to study the sensitivity of Lidar signal to some system characteristics, e;g., pulse energy, footprint diameter, 3) analysis of both simulated and experimental data to improve processing algorithms used to retrieve forest parameters, 4) exploration of the potential of low emitted laser energy at high repetition frequency for a vegetation Lidar mission. This research effort led CNES to move towards a new phase the vegetation Lidar mission LEAF, along with a high resolution hyperspectral mission, for in-depth experimental studies.