Sources of variability in canopy reflectance and the convergent properties of plants

Abstract

Summary: How plants interact with sunlight is central to the existence of life and provides a window to the functioning of ecosystems. Although the basic properties of leaf spectra have been known for decades, interpreting canopy‐level spectra is more challenging because leaf‐level effects are complicated by a host of stem‐ and canopy‐level traits. Progress has been made through empirical analyses and models, although both methods have been hampered by a series of persistent challenges. Here, I review current understanding of plant spectral properties with respect to sources of uncertainty at leaf to canopy scales. I also discuss the role of evolutionary convergence in plant functioning and the difficulty of identifying individual properties among a suite of interrelated traits. A pattern that emerges suggests a synergy among the scattering effects of leaf‐, stem‐ and canopy‐level traits that becomes most apparent in the near‐infrared (NIR) region. This explains the widespread and well‐known importance of the NIR region in vegetation remote sensing, but presents an interesting paradox that has yet to be fully explored: that we can often gain more insight about the functioning of plants by examining wavelengths that are not used in photosynthesis than by examining those that are. Contents Summary 375 I. Introduction 376 II. Physical properties of incident radiation 377 III. Sources of variability in vegetation reflectance 378 IV. The combined effects of multiple traits on whole‐canopy reflectance 383 V. Functional convergence among optically important traits 387 VI. Conclusions 389 Acknowledgements 389 References 390