THE EFFECT OF UNDERSTORY PALMS AND CYCLANTHS ON THE GROWTH AND SURVIVAL OF INGA SEEDLINGS

Seedlings of Inga fagifolia (L.) Willd. and I. pezizifera Benth. were planted into the understory of a Costa Rican rain forest to test whether the proximity of large-leaved dwarf plams and cyclanths affects seedling growth and survival and if so, whether that effect is primarily due to above or belowground processes. In two sites, seedlings were planted either near palms (or palm-like Cyclanthaceae) or nearby in sites with no overarching vegetation under 1.5 m. Half of the seedlings in each treatment were trenched to a depth of 30 cm by cutting all roots 25 cm from the seedling. The proximity of palms or cyclanths significantly affected growth and survival of both species. However, most of this effect could be attributed to loss of stem length due to herbivore or pathogen damage rather than to differences in growth rates. There was no significant effect of trenching on seedling growth. Vegetation data from ten widely distributed sites in the forest showed that seedling density was inversely correlated with the abundance of understory palms and cyclanths. Our data suggest that understory vegetation, especially broad-leaved palms and palm-like cyclanths, acts as a filter affecting the distribution and abundance of establishing seedlings.