Bridging the gaps between field-based ecology and remote sensing to estimate plant functional diversity: a systematic review

Understanding plant functional diversity across scales requires integrating field-based ecology and remote sensing, yet these disciplines differ in how traits are measured, and upscaled. We synthesized three decades of research to evaluate conceptual and methodological convergence between these disciplines. Our results reveal that field-based ecology has undergone longer conceptual development and covers a broader range of traits, while remote sensing has experienced rapid growth driven by technological advances. Despite these differences, both disciplines are increasingly converging on similar concepts. However, major gaps in empirical coverage persist across biomes in both disciplines. While vegetation-dominated ecosystems have been extensively studied, extreme ecosystems remain comparatively undersampled. Trait analyses demonstrate a broad conceptual flexibility in defining "functional traits", yet both disciplines converge on a core set (e.g., plant height, leaf area, and leaf nitrogen content), reflecting their central role in plant strategies and spectral detectability. Remote sensing approaches differ in whether functional diversity is inferred from spatially aggregated mixtures at the pixel or community level or from resolved individual plants. Our synthesis underscores the potential for methodological synergy. Harmonizing trait definitions, scaling assumptions, and computational steps is essential to building a unified, multiscale framework for monitoring functional diversity in the context of global change.