Characteristics of radiation at different heights within the canopy of a tropical seasonal rain forest in Xishuangbanna, Southwest China

Based on investigations of radiation of different wavelengths at full light and different heights of a tropical seasonal rain forest in Xishuangbanna,the temporal and spatial characteristics of radiation within the tropical seasonal rain forest are presented.The results show that diurnal radiation decreases from the top of tree downward in the cool foggy season,while in the dry-hot and rainy season,sometimes existed the phenomenon of radiation values at 9 m and 0 m higher than that at 25 m when sunspots appeared.In the cool foggy,dry-hot and rainy seasons,the values of the daily accumulation of solar radiation,infrared radiation and visible light at the measurement sites and the ratios of these daily accumulated values to those of full light all decreased with height.The ratios all showed the tendency of infrared radiation > total solar radiation > visible light.The diurnal values and daily accumulation of solar radiation,infrared radiation and visible light and the ratios of these daily values at sites to those of full light and the ratios of infrared radiation,visible light to total solar radiation all varied with season,in addition,the order of these values at different seasons changed with height.Due to leaf absorption in visible light,the ratios of infrared radiation to total solar radiation at different heights were bigger than those of full light,which were contrary to the ratios of visible light to total solar radiation.However,not only at the same season but different observation sites,but also at the same site but different seasons,the ratios of infrared radiation and visible light to total solar radiation all presented complicated situation.The results indicated the light temporal and spatial heterogeneity in vertical direction within the tropical seasonal rain forest.These characteristics would play a great role in plant growth,regeneration,succession,community architecture formation and mass and energy exchanges between forest and atmosphere.