| Summary: | High structural diversity amongst plant species in the arid winter rainfall region of southern Africa is common to other arid regions of the world. Details of the range and combinations of structural attributes in species, and within plant communities, are not widely known for southern African arid ecosystems. Hence little is known of how plant-form distributions vary within and between arid ecosystems. and of the environmental factors that may be responsible for any variations found. Nor is much information available on how phenological behaviour relates to the structural attributes of plant species. This study examined structural attributes of perennial plant species on the Worcester Veld Reserve, southwestern Cape. in relation to their distribution and phenology. Species were grouped on the basis of above ground structural and anatomical criteria. The distribution of species and plant-forms was assessed through a phytosociological survey along an environmental gradient in the area, and their phenology determined through qualitative and quantitative monitoring of species phenophases over a two year period. The results show that species of the predefined structural groups i) Co-occur throughout the area. but relative abundances vary from site to site and in relation to topography. aspect and the presence of Mirna-like mounds; ii) Phenological patterns for the flora overall are strongly seasonal, but the timing and periods of phenophases differ between, but are relatively uniform within, the defined structural plant groups. Since phenological patterns are indicative of resource-use patterns. these results indicate that the different plant-forms have different functional responses to the conditions of limited water availability and summer drought. This conceivably facilitates the co-existence of species in this water-limited environment. Habitat variability. which can be related to land-form patterns. is also implicated as a factor facilitating the co-existence of a diversity of species and plant-forms. Structural functional relationships known for arid region plants help to explain the relative uniformity of behaviour within plantform groups. and aid in understanding the ecological significance of distribution patterns of plant-forms in the arid landscape. The conclusion is reached that because of the close coupling between photosynthesis and water-use. the water storage potential and photosynthetic organ type are plant attributes which can serve as useful criteria by which arid region species can be grouped into ecologically meaningful categories or functional guilds. The formulation of a practical and meaningful functional classification is necessary to facilitate the understanding of complex vegetation patterns and processes within arid ecosystems. and allow for meaningful inter-ecosystem comparisons.
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