Abiotic determinants of the fynbos/succulent karoo boundary, South Africa

This study investigates the influence of texture, soil moisture and nutrient status on the growth and survival of seedlings of two typical fynbos (Leucadendron pubescens and Passerina vulgaris) and succulent karoo (Ruschia spp.) species, which grow in the boundary zone between these two vegetation types. Seedlings of each species were grown in shale-derived and sandstone-derived soils and under xeric and mesic regimes. Under the xeric regime, the shale-derived and sandstone-derived soils represented fine and coarse-textured soils, respectively. Under the mesic regime, the same soils represented nutrient-rich and nutrient-poor soils, respectively. The seedlings of both fynbos species died rapidly under the xeric regime, irrespective of soil type. In contrast, the succulent karoo seedlings survived for over 77 days without water. Under mesic conditions, the fynbos seedlings grew faster than the succulent karoo seedlings, irrespective of soil type. Fynbos seedlings appear to be directly limited by the environment (moisture and salinity), whereas succulent karoo seedlings may be limited by interactions with other plants.