Abstract
Abstract. Adding to the on-going debate regarding vegetation recolonisation (more particularly the timing) in Europe and climate change since the Lateglacial, this study investigates a long sediment core (LL081) from Lake Ledro (652 m a.s.l., southern Alps, Italy). Environmental changes were reconstructed using multiproxy analysis (pollen-based vegetation and climate reconstruction, lake levels, magnetic susceptibility and X-ray fluorescence (XRF) measurements) recorded climate and land-use changes during the Lateglacial and early–middle Holocene. The well-dated and high-resolution pollen record of Lake Ledro is compared with vegetation records from the southern and northern Alps to trace the history of tree species distribution. An altitude-dependent progressive time delay of the first continuous occurrence of Abies (fir) and of the Larix (larch) development has been observed since the Lateglacial in the southern Alps. This pattern suggests that the mid-altitude Lake Ledro area was not a refuge and that trees originated from lowlands or hilly areas (e.g. Euganean Hills) in northern Italy. Preboreal oscillations (ca. 11 000 cal BP), Boreal oscillations (ca. 10 200, 9300 cal BP) and the 8.2 kyr cold event suggest a centennial-scale climate forcing in the studied area. Picea (spruce) expansion occurred preferentially around 10 200 and 8200 cal BP in the south-eastern Alps, and therefore reflects the long-lasting cumulative effects of successive boreal and the 8.2 kyr cold event. The extension of Abies is contemporaneous with the 8.2 kyr event, but its development in the southern Alps benefits from the wettest interval 8200–7300 cal BP evidenced in high lake levels, flood activity and pollen-based climate reconstructions. Since ca. 7500 cal BP, a weak signal of pollen-based anthropogenic activities suggest weak human impact. The period between ca. 5700 and ca. 4100 cal BP is considered as a transition period to colder and wetter conditions (particularly during summers) that favoured a dense beech (Fagus) forest development which in return caused a distinctive yew (Taxus) decline. We conclude that climate was the dominant factor controlling vegetation changes and erosion processes during the early and middle Holocene (up to ca. 4100 cal BP).
Highlights
During the Last Glacial Maximum (LGM) and the early– middle Holocene, the vegetation history of the Alpine area records two main features: (1) treeline migration, and the spreading of taxa from various Glacial refugia, in response to long-lasting climate change, and (2) mixed forcing from long- and short-term climate and anthropogenic changes.During the last orbitally driven deglaciation, conifers and broad-leaved tree species benefitted from global climate improvement and glacier retreat in the Alps to colonise new available areas
Researchers are searching for studies that meet three criteria: (1) they have to be located in the key zone of south-eastern Alps, which was a potential route for tree immigration from southern Italy and the Balkans and for comparison with the nearby potential Euganean Hills refuge (Kaltenrieder et al, 2009); (2) a palaeovegetational archive must be present at highchronological and temporal resolution for the Lateglacial; (3) and pollen grains must be received from a large range of altitudes in its catchment
The Holocene climate in Europe is punctuated by numerous short-term cold events, such as Preboreal and Boreal oscillations (Bjorck et al, 1997, 2001; Fleitmann et al, 2007; Yu et al, 2010), the 8.2 kyr event (Wiersma and Jongma, 2010) and Neoglacial climate cooling at ca. 6000– 4000 cal BP (Magny et al, 2006b; Miller et al, 2010; Giraudi et al, 2011; Zanchetta et al, 2012; Vanniere et al, 2012)
Summary
During the Last Glacial Maximum (LGM) and the early– middle Holocene, the vegetation history of the Alpine area records two main features: (1) treeline migration, and the spreading of taxa from various Glacial refugia, in response to long-lasting climate change, and (2) mixed forcing from long- and short-term climate and anthropogenic changes.During the last orbitally driven deglaciation, conifers and broad-leaved tree species benefitted from global climate improvement and glacier retreat in the Alps to colonise new available areas. The spread of Abies, may have been different with the possible persistence at high altitudes in the southern slope of the Alps (Hofstetter et al, 2006) To address this question, researchers are searching for studies that meet three criteria: (1) they have to be located in the key zone of south-eastern Alps, which was a potential route for tree immigration from southern Italy and the Balkans and for comparison with the nearby potential Euganean Hills refuge (Kaltenrieder et al, 2009); (2) a palaeovegetational archive must be present at highchronological and temporal resolution for the Lateglacial; (3) and pollen grains must be received from a large range of altitudes in its catchment. 6000– 4000 cal BP (Magny et al, 2006b; Miller et al, 2010; Giraudi et al, 2011; Zanchetta et al, 2012; Vanniere et al, 2012) These rapid climatic changes are recorded throughout the Mediterranean region, but their characteristic effects can vary spatially In the open debate to assess the possible relationships between climatic change and impact of human societies, which has become a contemporary issue, palaeoenvironmental records are needed to gain a perspective of past processes
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