Patterns of change in reed cover and distribution in a seasonal riverine wetland in South Africa

Phragmites mauritianus is the dominant herbaceous species colonizing riveri ne habitats in the Kruger National Park, South Africa. These perennial syst ems are characterized by high annual and seasonal flow variability and a co mplex mosaic of patches of reeds, sand, water, rock and other vegetation. P atterns of increase and decrease in reed cover in the Letaba River were det ermined from aerial photographs covering a 54-year period. An initial perio d of reed expansion (1942-1965) was followed by a period of reed loss (1965 -1977) and subsequent gradual re-establishment (1977-1996). A spatially exp licit analysis of changes in reed distribution over an 8-year period (1988- 1996) showed that patches of reed vegetation are, in the short term, highly dynamic elements within the river landscape. Analyzing short-term, small-s cale change provides information which is not obtainable from long-term, la rge-scale studies. We propose that causes of reed expansion or decline cann ot be determined without an understanding of both long- and short-term patt erns of change.