XÑ§nwï@XÑ§n35(2), 1993, pp. 10`19
YAHTA, Hisashi: Estmation of light regimes in a forest floor using photographs and the effect on seedling growth of several species of Dipterocarps in a tropical rain forest
A methodology for the estimation of light environments under a forest canopy from hemispherical photographs of sites within the forest and a computerized technique using a common video camera and a cheap video scanner for image analysis is described. Estimated diurnal light intensity using this technique was compared with the measured data. Under cloudy conditions, the estimated data had a high positive correlation with the measured (r=0.966 maximum), whereas under clear conditions with some clouds, the estimated instantaneous data deviated from the measured data because of the distance between the photon sensors, one for open light and the other for forest sites. However, for the three hoursf means or the diurnal integrated data of the photosynthetically active photon flux density(PPFD), the measured data correlated strongly (r=0.971 and r=0.982, respectively) with the estimate from photographs.
Using the above technique, both relative light intensity
(RLI) for cloudy conditions, and also time esparated gap light index(GLI, the
ratio of integrated PPFD over one year inside and outside the forest) for clear
condition, were estimated in order to demonstrate a relation to the seedling
growth of the six species of Dipterocarps (Anisoptera
costata, Shorea seminis, S. ovalis,
S. academia, Hopea mengarawan, Cotylelodium burckii). RLI was highly
correlated to daily GLI calculated for a whole year, but not with time
separated GLI. The vertical growth was inhibited by strong morning light for S. ovalis and C. burckii, and by strong late afternoon light for S. academia.
This may imply that the vertical growth inhibition observed in high RLI is not
caused by strong mid day light, but by other factors such as the red light/far
red light ratio.
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