PARENT SESSION
Oral Session # 69: Forest Ecology IV: Communities.
Presiding: D Gavin
Thursday, August 7. 8:00 AM to 11:30 AM, SITCC Meeting Room 200.

Understory palms and cyclanths impose strong recruitment limitation on seedlings in a Neotropical rain forest.

Wang, Yung-Ho (Ophelia)^*,1, Augspurger, Carol¹, ¹ University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA

ABSTRACT- Recruitment limitation, which occurs when species either fail to reach or establish in sites suitable for regeneration, has been proposed as an important factor that controls population dynamics and species coexistence in tropical moist forests. Palms in some Neotropical forests dominate understory strata, and may cause seedling recruitment limitation because their umbrella-like architecture may prevent seed rain and cast deep shade. This study surveyed seedlings under dwarf palms/cyclanths in four habitats at La Selva Biological Station, Costa Rica. It compared seedling recruitment in 2001 and 2002 at control sites vs. sites under dwarf palms of two heights and two densities. Overall, dwarf palms/cyclanths had great density (2540 individuals/ha) and covered 20% of the understory in the primary forest. Overall, seedling growth, survivorship, density, and species richness were 23%, 37%, 34%, and 26%, respectively, lower at under-palm sites than at control sites. Each of these variables was greatest at control sites and lowest at high-density palm sites. Seedlings at different stages and of different taxonomic groups responded to the suppression differently. The main restriction by dwarf palms occurred on post-cotyledonous and woody seedlings. Percent canopy openness, leaf area index (LAI), and photon flux density (PFD) measured and estimated with hemispheric photos each indicated that light availability was greatest at control sites and lowest at high-density palm sites. However, overall seedling responses under a given palm were only weakly correlated with its light environment. The study revealed significant recruitment limitation under individual dwarf palms, with greatest negative effects where a palm was surrounded by nearby palms. This restriction by individual dwarf palms accumulates to a significant level at the landscape scale as well, based on the great dwarf palm density and coverage in the four habitats.

Key words: recruitment limitation, understory palms, Neotropical forest, seedlings