Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : Pollen studies in semi-arid areas : north east Iran and south west Spain

Auteur : Stevenson, A.C

Université de soutenance : University of London,

Grade : Doctor of Philosophy (PhD) 1981

Résumé
Fossil and modern pollen studies have been conducted in N.E. Iran and S.W. Spain, from which models of modern pollen movement in desert and mediterranean communities are proposed and compared. The modern pollen data was also used to aid interpretation of the fossil pollen diagrams from N.E. Iran and S.W. Spain. It was possible to differentiate in S.W. Spain many of the major mediterranean plant communities on the basis of their associated modern pollen rain, this however, was not possible in N.E. Iran. The fossil pollen diagrams from N.E. Iran revealed a relatively stable vegetational history, with possibly changes in the forest composition of the Caspian forests being reflected in changes in the long distance input to the fossil site. The diagrams from S.W. Spain, exhibit however, marked changes in the forest composition of the Doana area. The earliest diagrams dated to approximately 13,000 b.p. reveal the existence of a local sand dune succession, the long distance component of which reveals the possible presence of a cool moist forest on the Guadaiquivir plain at this time. The next fossil site is dated to approximately 4550 b.p. and reveals the presence of a mediterranean forest already heavily disturbed (possibly due to tectonic activity) which recovers only to be disturbed once again. This second disturbance may be due to an anthropogenic effect since large amounts of Vitis pollen are recovered from this time. Subsequently the viticulture is abandoned around the time of the Romans and the forest recovers only to be heavily disturbed once again as the Moorish influence acts on the vegetation. (The three main components of the forest vegetation are found to exhibit very different behaviour during the disturbances). The third site reveals the nature of the vegetation from 1740’s onwards when the site was thought to have last been disturbed by sand dune activity. The core reveals the existence of Scattered Pinus in monte negro vegetation from which the Pinus is subsequently progressively removed. The final stages of the diagram reveal the invasion of the site by Quercus suber and its subsequent dominance in the community.

Annonce (EThOS)

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