森林立地学会誌　森林立地35(2), 1993, pp. 10〜19

 

論　文

 

熱帯降雨林内の写真推定した光環境とフタバガキ科苗木の成長に及ぼす影響

 

矢幡　久

 

 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 hours’ 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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