Spectral transmission curves for a beech (Fagus sylvatica L.) canopy

Measurements were made at eighteen sites within a beechwood on a calm, uniformly overcast day in August, 1971. The sites varied in total incoming radiation (visible plus infra-red), being placed at various points on a light gradient from a clearing to deep canopy shade. Readings of spectral intensity were recorded from 380 nm to 1100 nm both inside and outside the wood. Transmission curves were then plotted for all sites. These showed a relative increase in transmission in the green (550 nm) and far red/near infra-red (beyond 700 nm) wavebands. When normalised, the transmission increment beyond 700 nm was shown to vary between sites, becoming less marked as total incoming radiation increased.