Fluxes of Visible and Net Radiation within a Forest Canopy

Abstract

In many ecosystem studies using models, and in studies of primary productivity, knowledge of the vertical distribution of radiant energy within the vegetative canopy is required. Anderson (1964) reviewed much of the work relating visible radiation to studies of crop photosynthesis. Anderson (1966), Cowan (1968, 1971) and Verhagen & Wilson (1969), among others, have presented theoretical analysis of light penetration through vegetation canopies. Investigations in crops (Allen, Yocum & Lemon 1964; Brown & Covey 1966) suggested that the distribution of net radiation with height or with cumulative leaf area index (LAI) is in agreement with the Lambert-Beer law relationship. Yocum, Allen & Lemon (1964) and Vezina & Boulter (1966) presented short-wave radiation transmission data by wavelength through canopies of corn, sugar maple, and red pine. Since these measurements were made above and below the canopy, any information about the energy levels within the canopy would have to be based on a LambertBeer law assumption which has commonly been used to describe transmission of shortwave radiation.