ASSESSMENT OF GAP FRACTION BY HEMISPHERICAL PHOTOGRAPH IN OIL PALM PLANTATION
Keywords:
Oil palm, digital camera, gap fraction, measurement, LAIAbstract
Gap Fraction is a crucial variable that governs interactions between light and vegetation and requiresaccurate modelling to predict light climate in the canopy, photosynthetic activity or canopy reflectance.It is the amount of open area within a canopy, which is not blocked by wood and foliage. The conventionalmethod used in determining the gap fraction is laborious, difficult and time consuming. Thus animage-based measurement using a camera system with a fisheye lens offers an alternative means forindirect measurement of the gap fraction in oil palms. In this study, a methodology was developed toassess the gap fraction of the oil palms by hemispherical photography as an indirect method and to findthe correlation between the gap fraction and Leaf Area Index (LAI). A total of 240 high quality hemisphericphotographs were recorded using a Nikon Coolpix 4,500 mega pixel digital camera, (Fuji,Tokyo 100-8331, Japan) with self-levelling mount and SLM2 type tripod (Delta-T Devices Ltd, UK).The study showed that the gap fraction decreased with an increase in the palm age. The gap fractionsobtained from the photographic method ranged from 0.51 to 0.18 for palms ranging from 2 to 16 yearsold. The gap fraction was strongly correlated (r = 0.99) with the LAI. Results indicate that the LAI wasnegatively correlated with the logarithm of the gap fraction, that is, where the gap fraction decreasedwith increasing LAI values. A good relationship (r = 0.85) was also found between the gap fraction andpalm age. The hemispherical photographic method seems a useful tool, which can confidently be usedto estimate the gap fraction of an oil palm plantation.
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