The ability to optically detect reflected and emitted photons from vegetation has transformed our understanding of forest ecophysiology, enabling detailed assessments of photosynthesis and evapotranspiration across scales. This chapter explores the links between physiological processes, remote sensing signals and broader ecosystem fluxes. By integrating remote sensing data across scales (leaf, tower, aircraft, and satellite), we capture the interactions between forest structure, function, and environmental conditions. We address scaling challenges and consider the convergence and divergence of remote sensing signals and forest ecophysiological processes. Convergence in plant traits creates predictable relationships between canopy structure and function, facilitating estimates of forest processes at large scales, while divergence arises from stressors and nuanced interactions at finer scales. Ultimately, we aim to clarify when and why these phenomena emerge and their significance for characterizing forest functional dynamics.