Leaf Aging Affects the Variability of Canopy Reflectance with Stand Development in Evergreen Chinese FIR Plantation

Abstract

Despite the long-term records of satellite observations, factors controlling the seasonal and interannual variations in canopy reflectance remain poorly understood. Leaf optical properties (LOP, including leaf reflectance and transmittance) changes as leaves age, and thus impact the seasonal pattern of canopy reflectance, i.e., the “leaf age effect”. Here, we combined the Geometric Optical Radiative Transfer (GORT) model with continuous field measurements of leaf- to stand-scale characteristics to simulate canopy reflectance in a Chinese fir plantation with stand development (1–33 yr). We found that canopy structure controls the variations in canopy reflectance during young stages (<10 yr) and that leaf age controls the variations in canopy reflectance after canopy closure. Moreover, we found that the “leaf age effect” get enhanced with stand development, with R2 increased from about 0.1 to 0.56, 0.67, 0.92, and 0.82 for young, half-mature, near-mature, and mature stages, respectively. This study reveals the stand age dependence of leaf age effect on canopy reflectance which improves our interpretation and understanding of satellite observations to study the ecosystem function of forests.