Valley floor vegetation, landform and process relations in the Baviaanskloof, South Africa (#121)
A large body of literature exists on the importance of hydrogeomorphic controls on vegetation composition and distribution patterns. Vegetation dynamics vary along river systems with hydrological processes, geomorphic setting, sediment supply and surface-groundwater interaction. Despite the longstanding realization that vegetation also controls fluvial geomorphic form and process, this interrelationship was typically ignored. Interactions between disturbances, sediment transport and vegetation growth often lead to development of distinct fluvial landforms of different ages occupied by specific plant communities. Complex feedbacks exist between these interacting variables. A study in the semi-arid Baviaanskloof River catchment in South Africa involving 13 study sites revealed the interdependence of river valley morphology, surface-groundwater interactions and vegetation in narrow and wide valley sections. PRIMER analyses showed a strong link between plant distribution patterns and water availability (R2 = 0.704). Two groups of sites were closely related to flow permanence. Wetted channel sites or sites with a near-surface groundwater table grouped closely while dry bed channel sites or sites with a deeper groundwater table grouped closely. The analyses indicated that the environmental variables which best explained the variation in vegetation at the differing geomorphic landforms were elevation and distance and fine and coarse sand. The different plant growth forms in turn affected the geomorphic landforms. Through for example, their influence on sediment deposition and erosion processes. Moreover, plant growth form determined root biomass which directly affected landform stability. The methods and procedures that were used to collate the data are briefly presented, together with detailed interpreted results.