Sarcopoterium spinosum from mosaic structure to matrix structure: Impact of calcrete (Nari) on vegetation in a Mediterranean semi-arid landscape

Sarcopoterium spinosum L. (S.p.) is a common type of dwarf shrub in the eastern Mediterranean area. This study focuses on the semi-arid south-western Judean foothills (Shephelah) in Israel, characterized by a hilly landscape with variable coverage of hard calcrete rock outcrops (Nari) on chalk. The following research questions were addressed: 1) What is the effect of calcrete rock outcrops on S.p. and the spatial composition of the vegetative landscape? 2) What are the landscape conditions in which S.p. dominates the vegetation? 3) What is the spatial structure and occupation strategy of S.p. in relation to rocky and non-rocky landscape surfaces? A field study was conducted to measure visual surface coverage of five components: S.p., shrub (excluding S.p. and including other dwarf shrubs and trees), annuals, rock, and bare soil. The results show that rock, an abiotic component, plays an important role in the semi-arid landscape of the research area. When rocky coverage is more than 14% of the surface, its presence contributes to high heterogeneity and advanced ecological niches, and governs the appearance and distribution of biotic components such as S.p. and others. Among the studied components, the relationship between rock and S.p. was found to be the strongest. Furthermore, rock and S.p. seem to fill interchangeable functions. As rock presence decreases, S.p. distribution increases. When rock coverage is less than 14%, S.p. becomes the dominant landscape component, covering 37%-77% of the surface, characterized by large patches with a high level of homogeneity along the entire slope. Our results show that the rock/S.p. ratio controls changes in the landscape structure varying from stable heterogenic mosaic to stable homogeneous S.p. matrix. (c) 2012 Elsevier B.V. All rights reserved.