The Distribution of Asphodelus Microcarpus and Associated Species on the Western Mediterranean Coast of Egypt

Abstract

This study is a quantitative analysis of the distributional behavior of Asphodelus microcarpus in relation to the main environmental factors. Its abundance was estimated in 40 stands covering most of the apparent physiographic and edaphic variations in an area extending about 500 km along the western Mediterranean coast of Egypt. In each stand, the number of shoots of A. microcarpus was counted in fifty 1—m2 quadrats, and its density and frequency were calculated. Variations in these two phytosociological characters were then evaluated in different types of habitat. Associated perennials were recorded in each quadrat and their relative frequencies estimated. These frequencies were used in ordering stands along there different axes according to the degrees of dissimilarity between them. This three—dimensional ordination was used to illustrate the phytosociological behavior of A. microcarpus and its relationship with other species. Quantitative estimations of conductivity and percentages of CaCO3, organic carbon total nitrogen, sand, silt, and clay were made for the soil in each stand. Also, the nature of surface, depth of soil, and physiographic position of each stand was rated. Variations in each of these environmental parameters, or their combinations, were then correlated with the distributional behavior of A. microcarpus. Variations in the abundence of A. microcarpus within each of the major types of habitat were found to be at least as significant as those between them. This indicated that local environmental variations had a substantial role in determining the distributional pattern of that species. The position of A. microcarpus in the ordination, which represented the phytosociological structure of the vegetation, was intermediate. The conclusion is that abundance of A. microcarpus is controlled mainly by the moisture availability and the total nitrogen and CaCO3 percentage in the soil. The moisture availability correlated significantly with more than 85% of the variation in its abundance. Its ecological amplitude in relation to local variations in this factor conformed roughly to that based on an geographical scale. Along the gradient of total nitrogen, the abundance of A. microcarpus exhibited a significant abrupt increase at the category of the highest value. In relation to the CaCO3 gradient A. microcarpus increased in abundance at medium categories and decreased toward low, as well as high ones. However, significant variation with either nitrogen or CaCo3 percentage was less than one—third of that with moisture availability, implying that moisture is ore important in controlling A. microcarpus distribution.