Natural Rehabilitation Potential of Riparian Zones After Alien Clearing in the Fynbos Biome – Phase 1: A Reference Study of Indigenous Seed Banks
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Riparian areas contribute significantly to the spread of many invasive species which alter the ecosystem and bring about significant water loss to the river system. These areas have therefore been targeted by many alien clearing programmes. Little attention, however, has been paid to rehabilitating these areas after clearing and the role that soil seed banks play in this process. This study aimed to assess the composition and viability of reference seed banks, to be used as a bench mark for conservation managers and landowners, when assessing post disturbance rehabilitation techniques. The focus was on soil seed bank composition of the riparian vegetation in four river systems within the fynbos biome of the south-western part of the Cape. Both mountain and foothill sections of the Eerste, Molenaars, Berg and Wit Rivers were sampled. Plots were located in relatively undisturbed fynbos/riparian areas, with less than 25% invasion. Two factors were taken into consideration when setting up the sampling plots, namely lateral (wet and dry bank) and longitudinal (mountain stream and foothill) zones. Vegetation data were collected on site and contrasted with the seedlings that emerged from the soil samples to compare diversity and vegetation groupings. The seed bank composition was found to have little overlap with the current aboveground vegetation. The mountain stream slopes of all rivers were found to have a greater diversity within the seed bank, particularly so under the influence of past intermittent fires. On a lateral scale, the transitional zone between wet and dry banks was found to have a higher seed bank diversity with representatives of both riparian and fynbos species.