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. · 3.73 Impact Factor
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ABSTRACT: Quaternary Geochronology, doi:10.1016/j.quageo.2012.12.004Quaternary Geochronology. 01/2013;
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ABSTRACT: Here we present a palynological and sedimentological record from a 96-cm sediment core covering the last 13 ka aiming to document palaeoecological changes in the central South Caucasus driven by climate and/or human impact. The core was retrieved from Lake Paravani (2073 m asl, 41°27′N, 43°48′E), located in the steppic grasslands of South Caucasus in the Samsari-Javakheti volcanic plateau. The geomorphological features observed on the plateau, including moraine deposits, suggest the presence of local glaciers reaching the lake level during the Last Glacial periods. Based on sediment and pollen data, three palaeoecological phases have been identified. The first phase spanning the Younger Dryas and the Early Holocene, corresponds to a steppic environment with a limited lake productivity driven by a cold and particularly dry climate. According to the Age–depth model, this phase ends near 8500 cal BP with the decline of Chenopodiaceae. The second phase starts with an important expansion of trees at 8300 cal years BP. The delayed afforestation recorded in Lake Paravani is a pattern that has now been recognised widely through the Black Sea region's more continental areas. As soon as the climatic and edaphic conditions were favourable, the main deciduous and coniferous trees expanded concurrently due to the proximity of glacial forest refugia located in western Caucasus. This second phase marked by a climatic optimum is also characterized by an increase in lake productivity. The third phase starts at 2000–3000 cal BP and corresponds to the decline of forests on the plateau and the expansion of herbaceous formations, leading to the present-day steppic environment. This deforestation phase is driven by the deterioration of the climate conditions and human impact.Quaternary Science Reviews 10/2013; 77:125-140. · 4.57 Impact Factor