Alexander's research focuses on how tropical forests respond to drivers such as drought, logging, fire, and climate change. He employs statistical models to understand the roles of species, microenvironments, forest structure, and functional traits in these responses on ecological time scales. Alexander leverages his background in electrical engineering to apply new technology to address these ecological questions. He developed and built a novel instrument to measure vertical light profiles from the canopy to the ground, and is using those data to constrain models of light availability in an elevation transect in Peru. He is currently using terrestrial (in collaboration with Wageningen University) and airborne LiDAR and airborne hyperspectral (in collaboration with the Asner Lab at the Carnegie Institution for Science) data to investigate the role of structure in forest productivity and responses of trees to stress.