Bark Spectral Signatures of One-Year-old Twigs of Different Shrubs Mainly Depend on Their Biochemical Traits

The interaction of bark with light depends on the optical properties of the bark, which are important for plant energy balance especially out of the vegetation season. Light reflected from bark also represents a kind of “bark spectral signature” that may be species-specific. This study examines some morphological, biochemical, and physiological traits that may affect the reflectance of the bark of 1-year-old twigs of different shrubs: Corylus avellana, Rosa canina, Ligustrum vulgare, Sambucus nigra, Cornus sericea var. flaviramea, and Viburnum lantana. High variability was seen across these species for morphological, biochemical, and physiological traits, except for photochemical efficiency of photosystem II. The bark spectral signatures differed significantly across these species. The reflectance peak for C. sericea var. flaviramea was in red, for C. avellana in green, and the other species showed a wide peak from green to red light. Redundancy analysis revealed that UV-B–absorbing substances and anthocyanin content, along with outer and inner bark thickness, together explained 61% of the reflectance spectra variability. Outer bark thickness was important for reflectance in UV, violet, and blue, while anthocyanins were important for reflectance in green and yellow. Chlorophyll b was negatively related to the reflectance of visible light. This study revealed great importance of biochemical traits for explaining bark reflectance. Differences in “bark spectral signatures” enable differentiation across species out of the vegetation season.