A Consideration for the Light Environmental Modeling under Tropical Rainforest Canopies

Photosynthetic Active Radiation (PAR) is the most important light source for plant photosynthesis. It is known that most of PARfrom solar radiation is well absorbed by the surface. The canopy is the surface in forest region, consists an aboveground portion ofplant community and formed by plant crowns. On the other hand, incident solar radiation is fluctuating at all times because offluctuating sky conditions. Therefore, qualitative light environmental measurements in forest are recommended to execute understable cloudy condition. In fact, it is quite a few opportunities to do under this sky condition. It means that the diffuse light conditionwithout the direct light is only suitable for this measurement. <br><br> In this study, we challenged the characterization the forest light environment as its representativeness under no consideration of skyconditions through analysis huge quantities of instantaneous data which obtained under the different sky conditions. All examineddata were obtained under the different sky conditions at the tropical rainforest canopy as one of the typical fluctuating sky conditionsregions. An incident PAR is transmitted and scattered by different forest layers at different heights. Various PAR data weremeasured with quantum units as Photosynthetic Photon Flux Density (PPFD) at different forest heights by the quantum sensors. Bycomparing PPFDs at different heights with an incident PPFD, relative PPFDs were calculated, which indicate the degree of PPFDdecrease from the canopy top to lower levels. As the results of these considerations, daily averaging is confirmed to be cancelled skyfluctuating influences.