Vegetation history and climate of the last 15,000 years at Laghi di Monticchio, southern Italy
ABSTRACT In southern Italy, vegetation contemporary with the end of the last glacial maximum, from 15,000 to 12,000 years ago, is shown by pollen-analysis to have been treeless and steppe-like in character. At 12,500 BP (years before present), Betula (birch) expanded into the steppe, quickly followed by Quercus (oak), Fagus (beech), Tilia (lime) and other tree genera of mesic forest. High percentages of Tilia point to a rich mesic forest that was contemporary with the ‘Allerød’ interstadial of northern Europe. A major decline in mesic trees with an accompanying return of Betula and steppe genera dated to 10,500 years ago identifies a ‘Younger Dryas’ climatic reversal. Betula and steppe genera were replaced by forest of Quercus and other mesic trees, notably Ulmus (elm), as the Holocene began. In the later Holocene, ca. 4000 years ago, Abies (fir), Carpinus betulus (hornbeam) and Taxus (yew) appeared. Abies and Taxus became extinct locally about 2500 years ago, either because of climatic change, or perhaps because of the effects of early agriculture. The Full-glacial climate is thought to have been cold and summer-dry with mainly winter precipitation. The Lateglacial ‘Bølling-Allerød’ Interstadial was summer-wet and warm. The response-surface based climate reconstruction indicates an early Holocene climate with markedly colder winter conditions than today, about −5°C compared with 3.9°C today as a mean temperature for the coldest month. The annual temperature sum is reconstructed as somewhat higher than today, 3500 degree days as compared with a calculated value of 2900 for today. The later Holocene had a climate like today's. Rainfall, and variation in its seasonal distribution, has been a critical determinant of the vegetation cover. The fossil pollen record at Laghi Di Monticchio has been complemented by diatom and plant macrofossil studies which provide evidence of former lake environments as well as data on the upland forest. Lake levels remained high during the Full- and Lateglacial with encroachment of shore vegetation during the Holocene. The sediments also have an exceptionally rich record of tephra falls which are of importance in dating and core correlation. Twenty-one macroscopically visible tephras occur in sediments of the last 15,000 years.
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ABSTRACT: Populations located at the rear-edge of a species' distribution may have disproportionate ecological and evolutionary importance for biodiversity conservation in a changing global environment. Yet genetic studies of such populations remain rare. This study investigates the evolutionary history of North-African low latitude marginal populations of Alnus glutinosa Gaertn., a European tree species that plays a significant ecological role as a keystone of riparian ecosystems. We genotyped 551 adults from 19 populations located across North Africa at 12 microsatellite loci and applied a coalescent-based simulation approach to reconstruct the demographic and evolutionary history of these populations. Surprisingly, Moroccan trees were tetraploids demonstrating a strong distinctiveness of these populations within a species otherwise known as diploid. Best-fitting models of demographic reconstruction revealed the relict nature of Moroccan populations that were found to have withstood past climate change events and to be much older than Algerian and Tunisian populations. This study highlights the complex demographic history that can be encountered in rear-edge distribution margins that here consist of both old stable climate relict and more recent populations, distinctively diverse genetically both quantitatively and qualitatively. We emphasize the high evolutionary and conservation value of marginal rear-edge populations of a keystone riparian species in the context of on-going climate change in the Mediterranean region.PLoS ONE 01/2013; 8(9):e75029. · 3.53 Impact Factor
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ABSTRACT: The Mediterranean Sea hydrology at the time of the Heinrich formation in the North Atlantic Ocean was analyzed by comparing sea surface temperatures (SSTs) and oxygen isotope composition of seawater (δw) changes during the past 75 kyr in two marine cores. These were compared to the palynological variations derived in the Mediterranean Sea core. During the last glacial the two oceanic SST records show similar and synchronous patterns, with several long-term cooling periods, ending by abrupt SST increases. At the time of the Heinrich events, cold SSTs and low salinity prevailed in the Mediterranean Sea. The freshwater budget was similar to the modern one, permitting the presence of a mixed forest on the Mediterranean borderlands. The post-Heinrich periods are marked by a freshwater budget decrease, limiting oak and fir tree growth in the Mediterranean region. Increase of precipitation or reduction of evaporation is observed before the Heinrich episode, and is associated with a well-developed mixed Mediterranean forest.Paleoceanography 10/1999; 14(5):626-638. · 3.30 Impact Factor
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ABSTRACT: The Marie cave, discovered to the north of Montpellier, Hérault (France), has yielded a fauna of 28 vertebrates, out of which 23 are small to large mammals, notably Mammuthusprimigenius. The few discovered artefacts have been attributed to the Upper Palaeolithic, which is in agreement with the two radiocarbon dates (31450 14C yr BP for the low level, and 28680 14C yr BP near the cave's entrance). The palynological study shows the existence (i) of a wooded steppe on the plateau, and (ii) of a riverine forest with alders in the valleys, associated with Mediterranean taxa. These data confirm the presence in Languedoc of Mediterranean species around 30000 yr BP, which qualifies the hypothesis of exclusively Spanish and Italian refuges during glacial periods.Comptes Rendus Palevol 05/2007; 6(4):241–251. · 1.01 Impact Factor