The role of perennial plants in preserving annual plant complexity in a desert ecosystem

Composition and structure of an annual plant community can be influenced by abiotic factors and strongly influenced by plant interactions. Due to the important contribution of perennial plants to desert ecosystems, i.e., (1) they act as a physical barrier against wind and radiation; and (2) they act as organic-matter donors and soil-moisture moderators, an attempt to distinguish between these two functions was made in this study. A long-term research covering three growing seasons (2006, 2007, and 2008) allowed us to examine the contribution of abiotic factors such as rainy years to the annual communities. At the study site, 50 Hammada scoparia shrubs and 50 artificial plants were randomly marked and placed to be used as a tool for distinguishing between the physical and the biotic components of annual plants. Soil samples were collected monthly and all annual plant species individuals were identified and counted during the three growing seasons of 2006, 2007, and 2008. Extreme differences found between annual measurements (biomass, plant density, species richness, and composition) were mainly detected during the wet growing season (2007) in comparison to the drier years (2006, 2008). Moreover, throughout the three years of the study, some annual species were more associated with the perennial shrubs while others were more associated with the open areas. Distinguishing between the two features of perennial plants - the physical barrier and the organic-matter donator/soil-moisture moderator, will allow us to elucidate the importance of perennial shrubs as long-term moderators of primary production in a desert ecosystem.