Senescence and spectral reflectance in leaves of northern pin oak (Quercus palustris Muenchh.)

Changes in the anatomy of oak leaves and their reflectance spectra from 450 to 850 nm were followed during autumnal senescence. Six sequential stages of senescence identified from green healthy to bronze dying leaves, and their reflectance properties are described. Changes in leaves related to the senescent stages, and factors exerting the most significant effects on reflectance, included the decline in chlorophyll, the synthesis of anthocyanins, the dissolution of organelles, and the dessication of tissues. Randomly collected leaves from sample trees were subsequently classified visually and examined for specific spectral features of the “red edge” as identified by Horler et al. (1983), Hare et al. (1984a,b), and Miller et al. (1985). The Gaussian model of the red edge, described by Hare et al. (1984a,b) and Miller et al. (1985), provided a reliable way of identifying the senescent classes. When compared with the non-Gaussian reflectance features by means of a discriminant function analysis, the latter proved to be less reliable.