RADIATION REGIME IN A TROPICAL DRY DECIDUOUS FOREST IN WESTERN MEXICO

Solar radiation (Qc), sunshine hours (n) and reflectance coefficients or albedo (A) were measured above, and photosynthetically active radiation (PAR) was measured above and within three levels in a tropical dry deciduous forest in western Mexico (19-degrees 30' N, 105-degrees 03' W). Values of Qc and n, and PAR and A showed a drastic change between rainy and dry season, and leafed and leafless period, respectively. The transmittance for solar radiation was high in dry season and showed a great variation on transition months from dry to rainy season. Midday albedo changed from 14 (August, leafed period) to 21% (May, leafless period). The transmittance of PAR within the forest was 0.92, 0.26 and 0.19 at levels of 10.0, 5.0 and 0.2 m above ground, respectively, in leafed period. The mean tree height was 11.0m. In leafless period, the transmittance was 0.75 and 0.46 at 5.0 and 0.2m levels.