Cyclic vegetational change and pattern in a community ofArthrocnemum macrostachyumin Mediterranean coastal desert of Egypt

The perennial shrubArthrocnemum macrostachyumdominates some of the saline habitats in the Mediterranean coastal desert of Egypt. The plants show a cyclic vegetational change and associated pattern. The shrubs have buried shoots which bear upright aerial shoots with clusters of branches. These trap wind-borne sand which then form hummocks. Each clump goes through a cycle of ‘pioneer’, ‘building’, ‘mature’, ‘degenerate’ and ‘eroded’ phases. The vegetation pattern is controlled byArthrocnemum macrostachyum. Progressive accumulation of fine sand, organic debris and humus around the plants ofArthrocnemum macrostachyumimproves the water-retaining capacity of soil on the hummocks;Cynodon dactylonis then able to establish itself and more frequently colonizes the hummocks than elsewhere, but it grows better wherever the abundance and/or performance ofArthrocnemum macrostachyumis low. Thus, one factor in the pattern ofCynodon dactylonis of environmental origin and the other is imposed upon it byArthrocnemum macrostachyum.