Light variation and carbon gain in rain forest understorey palms

Median daily total photosynthetic photon flux density (PPFD) in gap-edge habitats was 1-1.5 mol m-2, compared with 0.26-0.33 mol m-2 in adjacent understorey sites. Median daily PPFD in the gap centre increased with gap size. In the understorey, >80% of averages calculated for 5-min periods were <10 mu mol m-2 s-1, whereas most readings in the centre of a 150-m2 gap were between 50-100 mu mol m-2 s-1 and along the gap edge 20-50 mu mol m-2 s-1. For Asterogyne martiana and Geonoma cuneata, 2 dwarf species, median daily total PPFD did not increase from ground level to 1.5 m. Some 50% of all PPFD measurements <1.5 m were 0.18-0.39 mol m-2. At crown heights >1.5 m, median daily total PPFD increased to 0.51 mol m-2. Within clones of G. congesta, daily total PPFD increased significantly with crown height; median PPFD incident on crowns 3.5-4.0 m tall was 5 times greater than PPFD at heights