High-spectral resolution field and laboratory optical reflectance measurements of red spruce and eastern hemlock needles and branches

Abstract

Branch samples were collected from canopies of red spruce ( Picea rubens) and eastern hemlock ( Tsuga canadensis) on 11 and 12 September 1989 and 5 and 6 September 1990, and spectrally characterized by needle age class (first- and second-year). Needles from the branch samples were analyzed for complete optical properties (0.4–1.0 μm), pigment content (total chlorophylls), and anatomical (cellular) condition. Spectral differences between spruce and hemlock first- and second-year needles include differences in green peak reflectance features, red edge parameters, and amplitude features of the NIR plateau. Second-year needles of both species exhibit increased absorptance in the NIR when compared with first-year needles. Chlorophyll concentrations, as determined using both quantitative and empirical techniques [ratio analysis of reflectance spectra (RARS)] were greater in second-year needles in both species and highest overall in second-year hemlock needles. Substantial anatomical differences are seen between needles of the two species, as well as between age classes of the same species. Relative differences among total area occupied by cells, intercellular void space, and total needle volume likely contribute to the differences in the NIR response patterns observed. The reflectance spectra (0.4–2.5 μm) measured for single age-class branch segments of both species are similar in shape to reflectance spectra measured at the needle level. However, differences in the magnitude of reflectance are seen when branch and needle data are compared.