Morphology, dynamics, ecology and fauna of Arctotheca populifolia and Gazania rigens nabkha dunes

This paper examines some aspects of the development, growth and dynamics of nabkha (small, discrete dune hummocks) formed by two plant species, Arctotheca populifolia and Gazania rigens, including the colonization and utilization of the nabkha by terrestrial amphipods, Talorchestia capensis (Crustacea; Talitridae) and nematodes. Arctotheca populifolia has a prostrate growth habit, is relatively open, and has patches of bare sand scattered within the area occupied by the nabkha. Gazania rigens has a vertical, dense, multi-branching growth habit, displaying moderate horizontal growth. Gazania is four times aerodynamically rougher than Arctotheca and its sand trapping ability is significantly greater per unit area. Gazania consequently forms high, narrow, conical to elongate nabkha mounds, while Arctotheca forms low, semi-circular nabkha mounds. Gazania nabkha typically provide more food and litter, better shelter, and milder and more stable temperatures than Arctotheca nabkha. Above a minimum nabkha volume around 20,000 cm³ (core sample data) to 80,000 cm³ (whole nabkha samples) Gazania nabkha have greater numbers of nematodes and significantly greater numbers of amphipods dwelling within them than Arctotheca nabkha. Numbers of both increase with increasing size or volume of Gazania nabkha but decrease in Arctotheca nabkha above approximately 30,000 cm³. It is concluded that plant species growth and form greatly influences nabkha morphology, microclimate and habitat ecology. (C) 2000 Academic press.