Tropical forests are mainly unstratified especially in Amazonia and regions with lower fertility or higher temperatures

The stratified nature of tropical forest structure had been noted by early explorers, but until recent use of satellite-based LiDAR (GEDI, or Global Ecosystems Dynamics Investigation LiDAR), it was not possible to quantify stratification across all tropical forests. Understanding stratification is important because by some estimates, a majority of the world’s species inhabit tropical forest canopies. Stratification can modify vertical microenvironment, and thus can affect a species’ susceptibility to anthropogenic climate change. Here we find that, based on analyzing each GEDI 25m diameter footprint in tropical forests (after screening for human impact), most footprints (60-90%) do not have multiple layers of vegetation. The most common forest structure has a minimum plant area index (PAI) at ~40m followed by an increase in PAI until ~15m followed by a decline in PAI to the ground layer (described hereafter as a one peak footprint). There are large geographic patterns to forest structur..., ,早期探险家便已留意到热带森林结构的分层特性，但直至近年借助星载激光雷达（LiDAR，其全称为全球生态系统动态调查激光雷达，缩写为GEDI），方才实现对全球所有热带森林分层特征的量化分析。对森林分层特征的研究具有重要意义，据部分研究估算，全球绝大多数物种都栖息于热带森林的冠层之中。森林分层能够调控垂直方向的微环境，进而影响物种对人为气候变化的脆弱性。本研究通过对热带森林中每一个GEDI 25米直径激光光斑（已预先筛选掉受人类活动影响的光斑）进行分析后发现，绝大多数光斑（60%~90%）并不具备多层植被结构。最为常见的森林结构呈现如下特征：植物面积指数（Plant Area Index，PAI）在约40米高度处达到极小值，随后逐步升高，直至约15米高度时达到峰值，之后随高度降低至地表层，此类光斑后续将被称为单峰光斑。森林结构存在显著的地理分布模式……