The regeneration potential of the seed bank of an ephemeral floodplain in South Africa

Germination from the seed banks of ephemeral floodplain wetlands of the Nyl River in South Africa was quantified in a glasshouse experiment to examine the potential of the seed bank for revegetation. Sediments from three sites with different wetting and drying histories (permanent, seasonal and occasional inundation) were collected in late summer after flooding and germination but before the seed bank was replenished. Samples were flooded artificially after dry, wet or wet/dry pretreatment and germination was recorded. Samples were then dried and reflooded to assess germination from the residual seed bank. All sites had a species-rich germinable seed bank, The water regime history of each site did not influence the number of species or individuals present in any trial or pretreatment. More species and individuals germinated in the first germination trial than the second. Fewer species germinated from the samples collected from above the water line than from underwater Sixteen species (12 aquatic) and 1392 individuals germinated in the first trial. Most species from the field communities also germinated from the seed bank. Twelve species, including 2 new species, germinated from the residual seed bank. Many of the species from these wetlands have persistent seed banks with staggered germination of propagules. Species maintain themselves over space (sites), conditions (water regimes) and time (trials) by a range of life-cycle patterns. Wetland communities that depend on their seed banks for revegetation between wetting and drying events may be altered by human-induced changes to water regimes. (C) 1998 Elsevier Science B.V.