A Comparison of Montane and Lowland Forest in Ecuador: III. The Light Reaching the Ground Vegetation

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Abstract
In equivalent weather conditions more light energy reaches the ground vegetation of the montane forest than that of the lowland forest as diffuse light in cloudy and sunny conditions but curiously, less as sunflecks. Further, the montane canopy transmits relatively much more light in the 4 hr. around noon; and this is correlated with the finding from the hemisphere photographs that the montane canopy has more holes around the zenith than the lowland. The montane forest ground vegetation received during an 8-hr, day 40% more diffuse light in sunny conditions and about the same amount in cloudy conditions. The amount and quality of light reaching the ground vegetation is strongly influenced by the duration and distribution of sunny periods through the day. The interpretation of the differences in the light climate between the forests In terms of forest structure and the significance of the differences for the ground vegetation are discussed. The difficulties of extrapolating to long periods and possible improvements in methodology for further work are discussed. It is suggested that future studies should seek to embrace all regenerative phases and not only the high forest phase In any one area and that Evans''s area survey method in conjunction with hemisphere photographs has great potential as a means of studying light as an ecological factor.