Photographic Estimation of Light Environments on Forest Floors and Effects of Light on the Growth of Dipterocarp Seedlings
The light environment in the forest plays an essential role in gap dynamics and seedling growth following enrichment planting designed to rehabilitate degraded forests in the tropics, and light intensity relative to full sunlight (relative light intensity) is often used as an conventional index of light conditions under the forest canopy. However, under clear conditions, the relative light intensity in forest gaps is extremely variable, because direct beams of solar light (sunflecks) reach the forest floor at varying intervals and for varying duration. To avoid sunflecks giving distorted values, relative light intensity is commonly measured under cloudy conditions. Further, some authors recommend taking mean values from many points in a forest stand as the light index, especially when the solar altitude is high (Ando 1985). However, these measures are unsuitable for analyzing the relationships between light conditions and the growth of individual seedlings in the understory of forests precisely because the effect of sunflecks (which may be very significant) is ignored. Thus, direct and continuous measurements of light intensity under the canopy over long periods should ideally be used, but this requires a considerable number of quantum sensors and recorders.
KeywordsForest Floor Seedling Growth Height Growth Light Environment Diffuse Light
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