HIGH-SPECTRAL-RESOLUTION FIELD AND LABORATORY OPTICAL REFLECTANCE MEASUREMENTS OF RED SPRUCE AND EASTERN HEMLOCK NEEDLES AND BRANCHES

Branch samples were collected from canopies of red spruce (Picea ruben s) 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 mum), pigment conten t (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 param eters, 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 us ing both quantitative and empirical techniques [ratio analysis of refl ectance spectra (RARS)] were greater in second-year needles in both sp ecies 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 tot al needle volume likely contribute to the differences in the NIR respo nse patterns observed. The reflectance spectra (0.4-2.5 mum) measured for single age-class branch segments of both species are similar in sh ape to reflectance spectra measured at the needle level. However, diff erences in the magnitude of reflectance are seen when branch and needl e data are compared.