Abstract
Abstract Light intensity above the groundstoreys (120 cm) and inbetween the ground strata of a Riverine forest, a Carrasco forest and a terra firme Rain forest was recorded through two day periods of time in the rain season (April/May) and the dry season (August) of 1969. Measurements were undertaken between 6 a.m. and 18 p.m. in minute by minute intervals (51.840 readings). The relative frequency of light intensity was computed for seven intensity classes and three periods of time per day. The spectral composition of light was determined as relative frequency of light intensities for five filter ranges of wavelengths, seven intensity classes and three periods of time per day. The riverine forest (best light conditions for the undertorey plant communities) and the terra firme Rain forest (worst conditions) developed extremely oposite positions with respect to forest light climate, while the Carrasco forest showed up with a somewhat intermediate character, but with a strong shift to terra firme Rain forest conditions. The spectral composition of light received by the ground strata of all three forest stands was as follows: 1) light intensities peaked in the RG 630 filter range of wavelenths (5.920 Ǻ — 7.500 Ǻ), 2) a secondary intensity peak covered the VG 9 filter (4.420 Ǻ — 6.440 Ǻ) and 3) a less important secondary peak matched the BG 12 filter band (3.500 Ǻ — 5.150 Ǻ). Inbetween the understorey communities, spectral light intensities were pretty low and showed another considerable red-shift.
Highlights
Light is one of the important environ mental factors in plant life, primarily, because of the energy supply for photosynthesis
As forest structure and light climate are closely related, light environments of three forest stands in central Amazonia where comparitively studied to evaluate their characteristics away from the extremely troublesome forest inventories
The relative frequencies of light intensi ties for all three forest stands, as 1) the Riverine forest, 2) the Carrasco forest, and 3) the terra firme Rain forest were computed for seven intensity classes and three periods of time per day
Summary
Light is one of the important environ mental factors in plant life, primarily, because of the energy supply for photosynthesis. Comprehensive light climate evalu ations by Loomis, Williams and Moraes (1967) recorded the daylight factor for two terra fir me Rain forest sites near Belém with 1.1 percent and 1.5 percent, for a secondary forest (capoeira) with 1.8 percent, for an Igapó transect with 3.7 percent and for a varzéa forest community with 1.0 percent. Brinkmann (1970d) reported the daylight factor for a dense capoeira near Manaus with 0.7 to 1.9 percent, while the "spectral" daylight factor was : B G 12 — 0.7; VG 9 — 1.1; R G 630 — 1.5; R G 665 — 2.6 and R G N 9 — 3.0 (3 day average) All these evaluations confirm the fact, that daylight factor is really of little use in comparative studies on various forest com munities because the fractionizing effect is to small to be significant. The ratio total light (open) to total light (forest) has no ecological meaning at all
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