Title

Distribution and abundance of vascular epiphytes in tropical wet forests: A multi-scale approach

Date of Completion

January 2002

Keywords

Biology, Ecology

Degree

Ph.D.

Abstract

I examined the distribution, abundance and diversity of vascular epiphytes at three scales: within individual tree crowns, between tree species and along an altitudinal gradient. Within individual tree crowns and between species, I examined the effects of microclimate, tree characteristics, tree species, season and leaf phenology on the distribution, abundance and diversity of epiphytes in two tree species, Hyeronima alchomeoides and Lecythis ampla, at La Selva Biological Station in Costa Rica. The microenvironmental conditions within Hyeronima crowns were more homogeneous than Lecythis, which had a significantly greater PFD reaching the canopy during the dry season than Hyeronima and a doubling of PFD levels when it was deciduous. There was little overlap of epiphyte species among individuals within and between tree species and Hyeronima had significantly greater abundance of epiphytes than Lecythis. I ran a Canonical Correspondence Analysis on the epiphyte species richness and abundance with the microenvironmental and tree characteristics which explained only 12.4% of epiphyte distributions. High diversity, combined with the lack of community structure, suggest that tropical rainforest canopy communities are not in equilibrium and that this high diversity is maintained by a non-equilibrium mechanism such as intermediate disturbance or dispersal limitation, or perhaps by an equilibrium mechanism such as resource partitioning. ^ To assess diversity, distribution and abundance of vascular epiphytes along a contiguous old-growth elevational gradient in Costa Rica, I collected vascular epiphytes at five elevations, 2600m, 2000m, 1500m, 1000m, and 500m. All epiphytes were sampled in eight contiguous 0.5m x 0.5m quadrats along two lower branches in ten canopy trees at 2000m, 1600m and 1000m, nine at 500m and five at 2500m. I identified a total of 527 species of epiphytes in 121 genera in 49 families. The Pteridophytes were the most diverse group, 129 species, followed by Orchidaceae, 118 species. Cloud forest at 1000m was the most species rich site. ^ I recommend a rapid, standardized protocol to assess epiphyte diversity in situ. Two branches at differing heights in the canopy should be assessed to maximize microclimatic variation. The transects should be subdivided into quadrats which allows reference for distribution such as distance from the trunk, branch height, diameter, azimuth and angle. ^