PARENT SESSION
Oral Session # 88: Plant Ecology VII: Communities.
Presiding: N Turrill Welch
Friday, August 8. 8:30 AM to 12:00 PM, SITCC Meeting Room 100.

Environmental determinants of vascular epiphyte distribution and abundance in a tropical wet forest.

Cardelus, Catherine^*,1, ¹ University of Florida, Gainesville, FL

ABSTRACT- The community composition and distribution of vascular epiphytes is examined in relation to photosynthetic photon flux density, temperature, humidity and tree characteristics in the inner-crown of two emergent tree species, Hyeronima alchorneoides and Lecythis ampla, at La Selva Biological Station, Costa Rica. In the combined sample branch area of 32 m², 53 species were found. There was little overlap of epiphyte species among individuals of the same tree species or between tree species. Abundance patterns of vascular epiphytes were significantly different between the two tree species however, Hyeronima had significantly greater abundance of epiphytes than Lecythis, particularly for Pteridophytes. A direct gradient Canonical Correspondence Analysis of the relationship between epiphyte species distribution and the microenvironmental and tree characteristics explained only 12.4% of the variance in epiphyte species distributions in the inner-crowns. Within each tree species alone, however, the microenvironmental and tree characteristics explained at least 20% of the species distributions. High diversity, combined with the lack of community structure, suggest that tropical rainforest canopy communities are highly dynamic. High diversity may be maintained by a non-equilibrium mechanism such as intermediate disturbance or dispersal limitation.

Key words: diversity, epiphytes, microclimate