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Doctorat
Royaume-Uni
1975-1984
Pollen studies in semi-arid areas : north east Iran and south west Spain
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.
Page publiée le 16 février 2015, mise à jour le 15 janvier 2018