Holocene Landscape History of Southern Portugal

Abstract

To date, southern Portugal has been the focus of only limited palaeoecological research. In particular, the scarcity of dated pollen studies has meant that inferences regarding the vegetation history of the Algarve and related aspects of landscape evolution have had to be drawn from distant sites. Palaeoecological research has been hindered by the lack of suitable sites for pollen analysis. This thesis contributes to the understanding of Holocene palaeoenvironmental change in the Algarve region with new palynological data from intertidal, estuarine sediments. In a region without natural lakes, estuarine sediments deposited during the post-glacial marine transgression represent a valuable resource for pollen analysis. Presented in the thesis are the methods and results of sedimentary and palynological analyses of AMS radiocarbon dated sediment sequences from the estuaries of the Guadiana, Arade and Boina rivers. Sediment analyses, including loss-on-ignition, particle-size analysis and magnetic susceptibility, are used to characterise sedimentary units within the sequences and permit an interpretation of changing environments of deposition during the Holocene. The sedimentary analyses contribute to the understanding of the evolution of the Arade/Boina and Guadiana estuaries and changes in the littoral zone, and are critical to the interpretation of palynological material preserved in within the cores.Pollen analyses of the estuarine sediments provide detailed palaeoecological information regarding changes in local and wetland environments within the estuarine settings, and vegetation events in the wider landscape between c. 13,000 and 2000 cal BP. Critical to the analysis are both taxonomic precision and the rigorous discrimination of wetland and non-wetland taxa. Based on the new pollen records, this thesis provides the first account of Holocene vegetation history for the Algarve. Identified at the three sites is an early and mid-Holocene woodland vegetation characterised by Pinus, evergreen and deciduous oaks (Quercus spp.) and associated understorey shrubs and herbs. After c. 5000 cal BP, dramatic declines in arboreal pollen are recorded, associated with an increase in moor and heath taxa, notably Ericaceae and Cistaceae. The results permit a re-evaluation of the debated role of anthropogenic impact on the Algarve landscape. Finally, the results of both sedimentary and pollen analyses are placed in the wider regional context of the Iberian peninsula. Considered in the thesis are: a) the timing and nature of changes in coastal environments during the Holocene transgression, b) the impact of sea-level change on wetland environments, c) the characteristics of the early and mid-Holocene vegetation, and d) the evidence for major deforestation during prehistoric times.Examiners Dr Henry Lamb, University of Wales Aberystwyth; Mr Peter James, University of LiverpoolViva: Cambridge, 6 September 2005, Degree conferred: Cambridge, 28 January 2006