World wide, more than 1700 C_4 plant species have been identified since the work of Downton and Tregunna (1968) and Black (1971). Most of these studies focused on the classification of plant species as to their photosynthetic pathway types (C_3, C_4 and CAM), geographic distribution of C_4 plants and their relationships with climatic patterns. But very few have looked at the relations between C_4 species and vegetation dynamics, especially in deserts and dry regions. C_4 plants and their relations with dese...