The restoration potential of fynbos riparian seed banks following alien clearing

Riparian areas contribute significantly to the spread of many invasive alien tree species which alter the ecosystem by bringing about significant water loss and changing the natural flow regimes of the system. For this reason, many alien clearing initiatives initially focus on riparian areas but limited resources allows for little restoration to these areas after clearing. The aim of this project was to assess the composition and viability of riparian seed banks before and after invasion to be used by conservation managers and land-owners in assessing post-disturbance restoration requirements. The focus was on riparian seed bank composition in four river systems in the south-western part of the Western Cape province (the Berg, Eerste, Molenaars and Wit Rivers). Equal number of plots were selected in both relatively un-invaded (<25% IAP cover) and invaded (>75% IAP cover) sections of the rivers. The seedlings that emerged from the soil samples were compared in terms of diversity, species richness, similarity and assembly groupings. Findings show that invasion alters the assembly patterns within riparian seed banks. Species richness, diversity and similarity of species showed no clear pattern and was suggested to be site specific. It is suggested that after intesive alien infestation, restoration will only be successfull if a seed source is restored by re-planting certain key riparian tree species that are not present in the seed bank and follow-up treatements continue.