The Effects of Canopy Light on Sapling Growth in a Lowland, Primary Amazonian Forest

Abstract

Light is an important factor governing seedling establishment and tree growth in tropical forests. A series of hemispherical lens canopy pictures were taken in a long-term, permanent tree plot at Cocha Cashu Biological Station, Manu National Park, Madre de Dios, Peru in 2003 and 2008. From these photographs, canopy light models were constructed to investigate changes in understory light conditions over the five year period. The resulting light data was then correlated with tree sapling data from the same plot, to determine the relationship between canopy light and sapling growth at the site. Extensive analysis of the canopy pictures and calculated light values revealed two important findings. The first is that grouped series of hemispherical photographs yield data that is internally consistent, and whose values correctly characterizing light conditions within a given study location. The second finding is that hemispherical pictures are weakly autocorrelated, making any attempt to spatially or temporally correlate individual sets of light values difficult. As a result, the study is inconclusive, yielding no distinct trends in canopy light over the five year period nor any significant relationships between canopy light changes and sapling growth.