THE UNDERSTOREY LIGHT REGIME AND PATTERNS OF TREE SEEDLINGS IN TROPICAL RIPARIAN FOREST PATCHES

The understorey light regime and its influence on forest tree seedling distribution was examined in isolated riparian forest patches where large numbers of co-existing species have been found. Understorey light intensity was highest at the forest edge, approaching 13% of full sunlight, but rapidly decreased towards the forest interior. By 7-12 m, light levels had stabilized at <2.0%, comparable to light levels in the interior of continuous tropical forest. Total seedling densities were not correlated with variations in understorey light intensity, suggesting that rates of germination and establishment were similar throughout the forest. However, examination of seedling light sensitivity among six common riparian tree species revealed differences in distribution: five species had higher seedling abundance in the darker forest interior or at the brighter forest-patch edge while one species was indifferent to light variation. These results suggest that the riparian forest light regime has sufficient variation to support several regeneration strategies, despite the small patch sizes.