Abstract
Abstract. Photosynthetic Active Radiation (PAR) is the most important light source for plant photosynthesis. It is known that most of PAR from solar radiation is well absorbed by the surface. The canopy is the surface in forest region, consists an aboveground portion of plant community and formed by plant crowns. On the other hand, incident solar radiation is fluctuating at all times because of fluctuating sky conditions. Therefore, qualitative light environmental measurements in forest are recommended to execute under stable cloudy condition. In fact, it is quite a few opportunities to do under this sky condition. It means that the diffuse light condition without the direct light is only suitable for this measurement. In this study, we challenged the characterization the forest light environment as its representativeness under no consideration of sky conditions through analysis huge quantities of instantaneous data which obtained under the different sky conditions. All examined data were obtained under the different sky conditions at the tropical rainforest canopy as one of the typical fluctuating sky conditions regions. An incident PAR is transmitted and scattered by different forest layers at different heights. Various PAR data were measured with quantum units as Photosynthetic Photon Flux Density (PPFD) at different forest heights by the quantum sensors. By comparing PPFDs at different heights with an incident PPFD, relative PPFDs were calculated, which indicate the degree of PPFD decrease from the canopy top to lower levels. As the results of these considerations, daily averaging is confirmed to be cancelled sky fluctuating influences.
Highlights
Remote sensing is only one powerful tool to expand the plant physiological model-based approach spatial-dimensionally
We focus on the influence of fluctuating sky conditions to the diurnal and daily changes in the forest light environment, and we measure the incident Photosynthetic Active Radiation (PAR) on the top of canopy and the transmissive PAR with quantum units as Photosynthetic Photon Flux Density (PPFD) at different forest height under tropical rainforest canopy on diverse sky conditions
Exponential from the relations with relative PPFD with forest height, that is, there is a linear relationship between forest height and Leaf Area Index (LAI) in our study forest site
Summary
Remote sensing is only one powerful tool to expand the plant physiological model-based approach spatial-dimensionally. We focus on the influence of fluctuating sky conditions to the diurnal and daily changes in the forest light environment, and we measure the incident PAR on the top of canopy and the transmissive PAR with quantum units as Photosynthetic Photon Flux Density (PPFD) at different forest height under tropical rainforest canopy on diverse sky conditions. We consider the time representativeness of the forest light environment under different weather conditions. Our research site is the tropical rainforest in Lambir hills national park and the western part of Sarawak state, Borneo Island, Malaysia (fig.). Our research site is the tropical rainforest in Lambir hills national park and the western part of Sarawak state, Borneo Island, Malaysia (fig.1) This region is known as the typical tropical weather region without seasonal change.
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