The Australian Vascular Epiphytes: Flora & Ecology

Abstract

Firstly, recent literature dealing with the systematics and ecology of vascular epiphytes is reviewed, as are a selection of older key papers. The classification and terminology of vascular epiphytes is briefly reviewed and discussed and the system used here is delineated; tenns are defined, including a ntnnber of new and previously ill-defined ones. The Australian vascular epiphyte flora is then described in a tabulated list and in a more detailed, illustrated descriptive key (Appendix 1). The flora is next discussed in relation to its taxonomic composition, diversity and affinities biogeography, life forms and physiognomic forms, and diaspore dispersal methods; these are also briefly related to basic ecology of the groups. Next, physical ecological factors of epiphyte environments in Australia are investigated. This includes discussion of continental macroclimate and its bearing on the distribution of epiphyte-favoured vegetation types, particularly rainforests, and investigation of microclimate components at different levels within selected sites in five different rainforest subformations of the subtropics. The results of this show that microsites near the canopy are considerably brighter, drier and more temperature-extreme than are those near the tree trunk bases. Beginning with a review of relevant works, the synecology of epiphytes is next discussed and the system of study for use here is outlined. The epiphytic vegetation of five subtropical sites (those mentioned above) and a tropical one, are investigated using this system which involves marked plots and the recording of all trees and epiphytes within them. The data derived from these are used in conjunction with that mentioned above and other observations for comparison and discussion of such topics as epiphyte floristic diversity, population density, vegetational complexity, occurrence of different epiphyte forms, specificity of epiphyte/phorophyte relationships, phorophyte axeny and epiphyte-proneness, allelopathy and phorophyte age ef~ect. Observations and review on nest-epiphytes and succession are discussed. Some basic functions of CAM in two epiphytic orchids were investigated under field conditions and the results are discussed in relation to its adaptive significance; the results of a survey of CAM in the Australian epiphytes are discussed and from this and the former, it is concluded that CAM is a very important water-conserving mechanism particularly to the heliophilous epiphytes. Relevant literature is reviewed. It is generally concluded from all of the above that epiphytism has been developed by small, slow-growing plants to avoid competition for light and in doing so, they have had to concomitantly adapt to water-stress and nutrient deficiency.