Ring-forming plants in the Egyptian deserts

Abstract

The formation of annual growth rings is an imperative requirement for studying the dendroecological potential of plant species. Little is known about the distinctness of growth rings in the wood of desert plants in Africa, particularly in southern Mediterranean regions. To fill this knowledge gap, we collected and anatomically analyzed about 300 perennial desert plants from different areas in Egypt. Out of the 300 studied plant species, 94 species were identified as growth-ring forming plants. They belong to 78 genera and 33 families. Trees, shrubs/subshrubs, and perennial or short-lived herbs are represented by 7, 55, and 32 species, respectively. Trees and shrubs represent 7.4% and 58.5% of the total, respectively. The distinctness of growth rings in these species was indicated either by the type of wood porosity, fibers, marginal parenchyma layers or by a mixture of these characteristics. Ring porosity, fiber layer, and parenchyma were the main indicators for growth-ring distinctness in 77.7%, 60.6%, and 33.0% of growth-ring forming plants, respectively. We conclude that some of the desert plants form distinct growth rings depending on site conditions, while precipitation is the main driver for its formation. Further studies on the annual rhythm of xylem formation are required to confirm the annual nature of growth rings and potential dendroecological use of these plants.