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Pollen analysis of a 48 m AMS radiocarbon-dated sediment sequence from the Guadiana estuary provides the first record of Lateglacial and Holocene vegetation history in the Algarve province of Portugal. This paper focuses on the record of terrestrial pollen taxa, which document a series of forest expansions and declines during the period 13 000 cal. BP to 1600 cal. BP and provide insights into climate evolution in southwestern Iberia. The main vegetation phases identified in the Guadiana valley are (1) Lateglacial interstadial (Allerød) forest with Quercus and Pinus under a temperate, moist, continental climate; (2) a Younger Dryas forest decline (Quercus) and expansion of pinewoods, xeric scrub and open ground habitats (with Juniperus, Artemisia, Ephedra distachya type, Centaurea scabiosa type) under arid and cold conditions; (3) an early Holocene forest/scrub/open-ground vegetation mosaic developing under a warm, dry and continental climate; (4) a maximum of Quercus forest and thermomediterranean evergreen taxa (Olea, Phillyrea, Pistacia) reflecting a warm, moist oceanic climate between c. 9000 cal. BP and c. 5000 cal. BP; and (5) the expansion of shrublands with Cistaceae and Ericaceae under a drier climatic regime and increasing anthropogenic activity since c. 5000 cal. BP. Holocene episodes of maximum climatic aridity are identified in the record of xerophytic taxa (Juniperus, Artemisia, Ephedra distachya type) centred around 10 200 cal. BP, 7800 cal. BP, 4800 cal. BP, 3100 cal. BP and 1700 cal. BP. Regional comparisons suggest a correlation of arid phases across southern Iberia and northwest Africa, which can be related to abrupt North Atlantic coolings (Bond events). [ABSTRACT FROM AUTHOR]

This paper examines the mid- to late-Holocene (c. 6850-1160 cal. yr BP) environmental history of Sierra de Gádor in southern Spain. The local vegetation dynamics are reconstructed through the palaeoecological record obtained from a lacustrine deposit situated at 1530 m. Various hypotheses are considered to explain the vegetation dynamics apparent in the palaeoecological evidence, including climatic change, fire occurrence and human activity. Although the vegetation in this region is sensitive to climatic change, threshold events driven by ecological factors are also apparent. Climatic events include a thermo-mesophytic optimum with abundance of deciduous trees and maximum lake water level found from c. 6850 to 5500 cal. yr BP. In contrast, changes in the frequency of major fire episodes appear to have shaped interspecific relationships and vegetation change, especially from c. 4200 cal. yr BP onwards. Biotic properties of the ecosystem such as the inertia of established tree populations, interconnected with competition adjustments, appear also to have played a role. Over the last two millennia, overgrazing, combined with natural and/or human-set fires, appears to have pushed mountain forests over a threshold leading to the spread of grassland, thorny scrub, junipers and nitrophilous communities. [ABSTRACT FROM AUTHOR]

This paper begins to identify the relative roles of climate change, people and fire as factors in the late-Pleistocene and Holocene evolution of one of the most diverse terrestrial ecosystems in southern Australia. Our research illustrates that pollen from mediterranean-type heathlands can be recognized from sediments taken from small basins in semi-arid ecosystems. The use of pollen and carbonized particle analyses from sediment cores, in conjunction with ecological research on plant-fire relationships, establishes a role for palaeoecological techniques in the interpretation of long-term processes in semi-arid heathlands in Australia. Radiocarbon dates indicate that the treeless structure at our study site in the Little Desert of western Victoria has existed since at least the early Holocene. Pollen evidence indicates an increase in plant diversity, especially in Proteaceae and fire ephemerals, and a decrease in fire-sensitive taxa (e.g., Callitris spp., Allocasuarina muelleriana type) over the last 4000 years. This decline occurs in conjunction with increases in the frequency of carbonized particles. [ABSTRACT FROM AUTHOR]