Habitat and Plant Communities in the Egyptian Desert: V. The Limestone Plateau

Abstract

This is an ecological survey of a 2000 sq. km. area of the limestone desert extending to the east of the Nile Valley. The principal ecogeo-morphological systems are: (1) the drainage systems (wadis); (2) the limestone erosion surfaces; and (3) the sand-and-gravel formations. (An account of the third system was given in Part IV of this series of papers). The drainage systems are classified into: (a) mature wadis (fossil river systems); (b) wadis with long but shallow courses (fossil juvenile rivers); and (c) wadis gradually cutting their channels backward across the limestone plateau (result of erosional processes operative under present climatic conditions). Type (c) includes four units representing sequential stages of its development. The erosion surfaces are associated with bands of dolomitic or silicified limestone that intercalate the less resistant massive beds of limestone. There are three main types of erosion surfaces: (1) plateau surface, (2) hamada, and (3) erosion pavement. On a geomorphological basis the authors recognize 7 ecological units each with a recognizable type of plant growth. Four of these geomorphological units represent stages in the development of the drainage runnels and it is suggested that the plant growth changes from one type to the next as the runnel changes in the course of its development: an example of allogenic succession.