Size structure and dynamics of the common shrubs in Omayed Biosphere Reserve in the western Mediterranean coast of Egypt

Abstract

The population structure of 15 common shrubby species of the Omayed Biosphere Reserve (Egypt) was evaluated in terms of size distribution. These species are 3 phanerophytes (Lycium europaeum, Phlomis floccosa and Thymelaea hirsuta) and 12 chamaephytes (Anabasis articulata, Artemisia herba-alba, Artemisia monosperma, Arthrocnemum macrostachyum Deverra tortuosa, Echiochilon fruticosum, Gymnocarpos decander, Haloc-nemum strobilaceum, Helianthemum lippii, Limoniastrum monopetalum, Noaea mucronata and Suaeda vera). The size estimations were used to classify the population of each species into 9 size classes : the first and second classes were chosen to represent the seedling and juvenile stages. The absolute and relative frequency of individuals and mean height, diameter and height to diameter ratio per individual in each size class were also determined. The present study indicated the size structures of the investigated species were belonged to 6 types of size distributions : more or less inverse J-shaped distribution (e. g. Halocnemum strobilaceum, Echio-chilon fruticosum and Helianthemum lippii), positively skewed distributions towards the small (i. e. young) individuals (e. g. Lycium europaeum, Arthrocnemum macrostachyum and Anabasis articulata), more or less J-shaped distribution (e. g. Noaea mucronata and Artemisia monosperma), approximately symmetrical (i. e. bell shaped) distribution (Phlomis floccosa), bimodal size distribution (e. g. Thymelaea hirsuta, Limoniastrum monopetalum and Suaeda vera) and more or less stationary size distribution (e. g. Gymnocarpos decander, Deverra tortuosa and Artemisia herbaalba).