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, Arctot heca populifolia and Gazania rigens, including the colonization and utiliza tion of the nabkha by terrestrial amphipods, Talorchestia capensis (Crustac ea; Talitridae) and nematodes. Arctotheca populifolia has a prostrate:growt h habit, is relatively open, and has patches of bare sand scattered within: the area occupied by the nabkha. Gazania rigens has a vertical, dense, mult i-branching growth habit, displaying moderate horizontal growth. Gazania is four times aerodynamically rougher than Arctotheca and its sand trapping a bility is significantly greater per unit area. Gazania consequently forms h igh, narrow, conical to elongate nabkha mounds, while Arctotheca forms low, semi-circular nabkha mounds. Gazania nabkha typically provide more food an d litter, better shelter, and milder and more stable temperatures than Arct otheca nabkha. Above a minimum nabkha volume around 20,000 cm(3) (core samp le data) to 80,000 cm(3) (whole nabkha samples) Gazania nabkha have greater numbers of nematodes and significantly greater numbers of amphipods dwelli ng within them than Arctotheca nabkha. Numbers of both increase with increa sing size or volume of Gazania nabkha but decrease in Arctotheca nabkha abo ve approximately 30,000 cm(3). It is concluded that plant species growth an d form greatly influences nabkha morphology, microclimate and habitat ecolo gy. (C) 2000 Academic press.