Spectral Distribution of Light in the Forest

Abstract

Spectral distributions of shade light between 400 and 740 mm were measured under corn, sugar maple, oaks, pines, and spruce with a portable recording spectrophotometer. Differences were found between hardwoods and softwoods and between clear cloudy days. An energy maximum at 550 nm, a minimum at 670 to 680 nm, and a very high maximum in the near infrared occurred under all species. Four components of light within a plant canopy can be distinguished: both beam solar radiation and diffused sky radiation are transmitted both directly and indirectly (reflected and scattered). Separate consideration of each of these components leads to great understanding of similarities and differences between light regimes in different stands.

Transmissivity of solar radiation within a <i>Picea sitchensis</i> stand under various sky conditions

“…This aspect of light quality has received much attention. The decline in the red : far-red ratio has long been known and has been linked in numerous studies to aspects of photomorphogenesis (see reviews by Federer and Tanner, 1966;Smith, 1982;Woodward, 1983;Morgan et al, 1985;Endler, 1993). In the present study, we have found that the red : far-red ratio in the canopy is much lower under clear skies (Hertel et al, 2011), indicating a lower photomorphogenical "light quality" (sensu Smith, 1982) than under diffuse conditions.…”

“…The diffuse radiation inside a forest canopy includes the fraction scattered by the foliage itself as well as radiation transmitted through the leaves and through the many gaps in the foliage (Muller, 1971;Grant, 1997). Sunflecks -their size, shape, duration and spectral distribution -depend on the orientation and inclination of woody and photosynthesising elements within the forest canopy as well as the position of the sun in the sky (Federer and Tanner, 1966;Norman and Jarvis, 1974;Pearcy, 1990;Chazdon and Pearcy, 1991;Grant, 1997). The way plants respond to sunflecks may vary, and in some shade plants this response (saturation of photosynthesis, stomatal regulation or possibly photo-inhibition) may be crucial to effective gas exchange and photosynthetic production (Sellers, 1985;Leakey et al, 2003).…”

A comparison and correction of light intensity loggers to photosynthetically active radiation sensors

“…PAR is defined as the rate of electromagnetic radiation received on a surface with wavelengths from 400 to 700 nm, which corresponds to light energy absorbed by photosensitive pigments with units of µmol photons m -2 s -1 (Brooks 1964;Federer and Tanner 1966;Booth 1976). The measurement of PAR under water presents a number of challenges, such as light scattering and attenuation with depth, as well as differences among the spectral responses of different sensor types.…”

Alguns aspectos ecofisiológicos de floresta tropical umidade terra firme ()

“…A radiação solar que atinge o topo das copas das árvores está bem próxima do infravermelho enquanto a que atinge o piso da floresta é muitas vezes menor em intensidade e qualidade, porque ela foi absorvida pelas ciorofilas das folhas das plantas dos estratos superiores. Federer & Tanner ( 1966) acharam que a variação de luz no piso da floresta depende do índice de área foliar dos estratos supe· ri ores.…”