Development and distribution of the epiphytic flora in an Amazonian savanna in Brazil

Abstract

The abundance and distribution of epiphytes were studied in a plot of about one third hectare of Amazonian savanna close to the city of Humaitá (7°31′ S, 63°00′ W; altitude ≈ 50 m). Non-vascular epiphytes (lichens and bryophytes), apparently undergo succession on trunks and branches of their host trees. While lichens dominate in young trees, and usually diminish in quantity on older ones, bryophytes are more abundant on older trees and seem to surpress the lichens. In total, 118 juvenile and adult individuals of 7 vascular epiphyte species (Catasetum saccatum: 65 individs., Polypodium decumanum: 33 individs., P. hirsutissimum: 16 individs., Polystachya estrellensis, Polypodiaceae sp., Gesneriaceae sp. and Araceae sp.: 1 individ. each) were found on 18 of the 111 tree individuals of the plot The furrowed and persistent bark of Physocalymma scaberrimum-trees seems to offer by far the best conditions for settlement and growth (average 2 epiphytes per tree). On the other hand, the flaky deciduous bark of Curatella americana and the smooth one of Cordia bicolor (averages about 0.2 epiphytes per tree) apparently make settlement more difficult. As much as 113 epiphytes (almost 96 %) were found on 15 trees higher than 4.5 m, whereas only 5 (about 4 %) had settled on 3 lower ones. Further, there appears to exist a positive correlation between density of vegetation and number of epiphyte individuals. Since the humid Amazonian climate permits vascular epiphytes to grow even in strongly insolated open savannas, the factors which determine their development seem to be the specific surface characteristics (mainly bark) of the host trees, the age of the trees, and also the density of vegetation. However, because of the low number of epiphyte bearing trees within the investigated plot, none of these three chracters is statistically significant.