Summary1. Vegetative growth in vascular epiphytes is assumed to be severely limited by intermittent supply of water and nutrients, but experimental evidence for this notion is meagre. The effects of water, nutrient supply and light on growth were studied in an epiphytic bromeliad, Vriesea sanguinolenta Cogn. & Marchal (syn. Werauhia sanguinolenta ) in a large forest gap in a lowland forest of Panama, in a full-factorial design. To investigate ontogenetic drift, three plant-size classes ( ≈ 5, 15 and 35 cm leaf length) were included in the experiment. 2. Water supply had the strongest influence on growth, but the magnitude of this effect differed considerably among size classes. Nutrient supply affected growth only in small and intermediate-sized plants. More light (60% of direct irradiation) tended to decrease growth rates compared to 30% irradiation. 3. Small plants showed by far the highest potential to adjust their relative growth rate (RGR) in response to favourable growing conditions. 4. Despite these size-related differences, absolute RGRs were extremely low compared to studies with other plant groups, confirming the notion that vascular epiphytes are inherently slow-growing plants.

The epiphytes on a given tree species are not simply a random sample of the local species pool, but there are no indications of host specificity either.

G. 2005. Long-term population dynamics of the epiphytic bromeliad, Werauhia sanguinolenta . Á/ Ecography 28: 000 Á/000.The population dynamics of the epiphytic bromeliad, Werauhia sanguinolenta , growing in the moist tropical forest of Barro Colorado Island, Panama, was studied for seven years from 1997 through 2004. In contrast to the generally held notion of the great importance of moisture availability for growth and survival of vascular epiphytes, no demographic process showed a significant correlation with the amount of annual precipitation or the varying number of rainy days per year. Most deaths, for example, were rather related to substrate instability (tree falls, branch breakage, or flaking bark) in all but the smallest size classes. We found evidence for both competition and facilitation. Elasticity analysis revealed that the finite rate of population increase, which invariably exceeded unity, was mostly influenced by survival (stasis) and to a lesser extent by growth, and very little by fecundity. In contrast to earlier reports on disastrous outbreaks of herbivores in this epiphyte species, the long-term impact of herbivory on the population dynamics of W. sanguinolenta was negligible. Being at least facultatively autogamous, reproduction seems to be controlled by resource availability alone: this is suggested by long intervals between reproductive events, and a decrease in size and an increased mortality after reproduction. We conclude that the demography of this epiphytic bromeliad is probably influenced at least as much by biotic factors (i.e. the dynamics of the substratum) as by abiotic limitations.G. Zotz (gerhard.zotz@unibas.ch), Botanisches Inst. der Univ. Basel, Schö nbeinstrasse 6, CH-4056 Basel, Switzerland. Á/ S. Laube, Fachber. Biologie, Abt. Allgem.

Question: What are the qualitative and quantitative long‐term changes in the vascular epiphyte assemblage on a particular host tree species? Location: Lowland rain forest of the San Lorenzo Crane Plot, Republic of Panama. Methods: We followed the fate of the vascular epiphyte assemblage on 99 individuals of the palm Socratea exorrhiza by three censuses over the course of five years. Results: The composition of the epiphyte assemblage changed little during the course of the study. While the similarity of epiphyte vegetation decreased on individual palms through time, the similarity analysed over all palms increased. Even well established epiphyte individuals experienced high mortality with only 46% of the originally mapped individuals surviving the following five years. We found a positive correlation between host tree size and epiphyte richness and detected higher colonization rates of epiphytes per surface area on larger trees. Conclusions Epiphyte assemblages on individual S. exorrhiza trees were highly dynamic while the overall composition of the epiphyte vegetation on the host tree species in the study plot was stable. We suggest that higher recruitment rates, due to localized seed dispersal by already established epiphytes, on larger palms promote the colonization of epiphytes on larger palms. Given the known growth rates and mortality rates of the host tree species, the maximum time available for colonization and reproduction of epiphytes on a given tree is estimated to be ca. 60 years. This time frame will probably be too short to allow assemblages to be ever saturated.

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