Light Environment in Tropical Rain Forest of Central Amazonia

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.