Analysis of the vegetation structure in the savanna - tropical forest transition of northern South America using The Global Ecosystem Dynamics Investigation (GEDI) data

Abstract:

The savanna - forest transition in the tropics has a large and complex variation in vegetation structure both vertically and horizontally. 3D-imaging technologies provide detailed high-resolution measurements of the vegetation structure. However, the use of these observations globally faces practical challenges due to spatio-temporal gaps and operational restrictions, mainly in tropical regions. NASA’s Global Ecosystem Dynamics Investigation (GEDI) is the first quasi-global (51.6°N-51.6°S) LiDAR (light detection and ranging) observations of 3D vegetation structure at a footprint resolution of 25 m. Here we use GEDI data (GEDI02_Bv001) to analyze vegetation structure in the savanna - tropical forest transition of northern South America, using canopy height, canopy cover, total Plant Area Index (PAI), maximum Plant Area volume Density (PAVD), and vertical profile of PAI and PAVD as vegetation structure descriptors. Despite contrasts between savanna (open-canopy) and forest (closed-canopy), our results show a gradual variation along the transition in canopy height, canopy cover, total PAI, and maximum PAVD. Our results support that the savanna- forest transition in tropical regions can be described as a grassland - forest continuum. Results also indicate that GEDI data allow a better characterization of vegetation lower than 5 m in height, mainly in savanna, an improvement from other global databases (e.g. MODIS). Further, our study illustrates the potential of GEDI data to advance in the characterization of large-scale patterns of vegetation structure in tropics, key for supporting biogeography, and macroecology studies relevant in the phase of current ecosystem changes.