THE SPECTRAL COMPOSITION OF NEAR ULTRAVIOLET AND VISIBLE RADIATION BENEATH FOREST CANOPIES

Abstract

The spectral composition of near ultraviolet and visible radiation in the open and in pure stands of Pinus resinosa Ait. and Acer saccharum Marsh was determined for cloudless, hazy, and overcast conditions. In the open, the spectral composition of light on clear and overcast days differed significantly only in quantity. Beneath the forest canopy the quality of light was changed greatly with respect to the open when the incoming radiation was direct sunlight. The selectivity of absorption and reflection in the visible spectrum by the deciduous canopy was shown quite conclusively while the conifer canopy appeared to be fairly neutral. On overcast days and during the leafless period of the deciduous canopy, transmission of the incident radiation was very high while the change in light quality appeared to be slight. The results are discussed in relation to the light-intercepting capacities of the leaves of the different species, the light climate in the forest, and silvicultural management.