Optical properties of canopy elements in the boreal forest

The spectral optical properties (e.g. reflectance and transmittance) of deciduous leaves, coniferous needles, and other canopy elements such as twigs and bark were investigated for several boreal forest species from May through September, 1994, as a part of the Boreal Ecosystem-Atmospheres Study (BOREAS) in Saskatchewan, Canada. Mature (>50 y) and young (<15 y) stands were examined for jack pine (Pinus Banksiana Lamb.) and for quaking aspen (Populus tremuloides Michx.) with its understory shrub, hazelnut (Corylus americana Walt.). The black spruce (Picea mariana (Mill.) BSP) stand was mature. Shoots/leaves from the upper and lower canopies were excised for laboratory measurements. For the conifers, the current and previous two age classes were examined. The Daughtry et al. (1989) integrating sphere method was revised and the measurement protocol restricted, for use with their published equations. Significant differences in optical properties were found in leaves/needles for different species or stands over the growing season, for canopy position (top vs. bottom), and age class (for conifers). These fundamental measurements are important for understanding the dynamics of shoot-level absorptance of solar energy for physiological processes. They are also critical for interpreting remotely acquired (e.g. aircraft, satellite) canopy reflectance observations, and for parameterizing radiative transfer simulations for remote sensing and carbon balance predictions