Spatial distribution of vascular epiphytes (including hemiepiphytes) in a lowland amazonian rain forest (Surumoni crane plot) of southern Venezuela

The mobile crane of the Surumoni project allowed for the first time ever a complete inventory and spatial description of the epiphytic vegetation of a tropical lowland rain forest plot (1.5 ha), at La Esmeralda on the upper O rinoco River, Venezuela. A total of 778 individual vascular epiphytes of 53 species was found, dominated by 19 orchid species and 14 species of Aracea e. Fifty percent of all individual plants were obligate ant-garden epiphyte s. The distribution of epiphytes was highly dumped and not random. The clum ped occurrence of holoepiphytes (complete life cycle on host tree) was the consequence of the rarity of suitable phorophytes (host trees; e.g., size a nd age) in the plot and the preference of ants for gaps where most of the a nt-garden epiphytes were found. In comparison, hemiepiphytes were distribut ed more evenly because of greater independence from tree suitability. The d ispersal modes of epiphytes did not explain their distribution patterns. Th ere was no consistent difference in distribution between anemochorous and z oochorous epiphytes, presumably because availability of suitable substrate is the more important factor for epiphyte establishment and growth. Whereas the vertical distribution of epiphytes could be attributed largely to dete rministic factors such as physiological adaptation and requirements, horizo ntal distribution appeared to be governed by suitable substrate, which in t urn seemed to be governed by stochastic gap formation.