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Communication Dans Un Congrès Année : 2014

The origin of the open landscapes of the highlands of Gredos (central Spain) during the Holocene: a pedoanthracological approach

Résumé

The Central Range of the Iberian Peninsula, arranged SW-NE, constitutes the boundary between the Duero and Tagus basins. It holds the highest altitudes (>2500 m a.s.l.) at its middle-west: the Gredos mountains, a strong siliceous massive of this submediterranean range. The current absence of natural forests at the highlands of Gredos (Central Iberian Range) has inspired controversial interpretations and remains today as a genuine feature of these mountains. In contrast, the available data about the vegetation history of the region indicates the existence of woodlands throughout the mid and late Holocene. Pollen records suggest that pinewoods have dominated during the mid- to late- Holocene, whereas the abundant macro- and mega-fossils studies support a prominent role of pines (mainly Pinus syvelstris) and birch at high altitudes (above 1300 m a.s.l.), especially during the late Holocene. Historical archives document the demise of forests since the Middle Ages and the intensification in the use of the pastures of the highlands of Gredos since the fourteenth century. No signs of proto-historic human presence have been still reported at the highlands but its influence has been well documented at lower altitudes, North and South of the Range. In this context we made the first pedoanthracological sampling in the region, in order to obtain information about the vegetation history at high altitudes, including treeline location in the past and the role played by shrublands. Five soil profiles across an altitudinal transect from 1800 m.a.s.l. to 2200 m.a.s.l. were sampled at the north slope of the Central Massif of Gredos, at the heart of Gredos range. Dated macrofossils (charcoals) indicate the occurrence of fire events since the early-Holocene (ca 9700 cal yr BP) until the recent-Holocene (ca 1000 cal yr BP), with several intermediate dates (ca 9000, ca 8400, ca 3700 and ca 2100 cal yr BP). The charcoal assemblages show a strong dominance of Leguminosae shrubs throughout the whole Holocene, accompanied by Betula sp. and Maloideae. This suggests the long-term occurrence of shrublands, probably similar in taxomonic composition to those occurring today, not detected before presumably because of their limited pollen production. We interpret the local presence of birch as scattered invidious or as belonging to small patches of forest among the dominant Leguminosae shrublands. On the light of these preliminary results, the Holocene treeline could be marked by Betula sp around 2000 m.a.s.l., as had been pointed by pollen studies in the westernmost part of the Central Range. Deciduous Quercus has been detected in the lower charcoal pit at 1800 m.a.s.l. which is coherent with current ecological data that report the occasional presence of this taxon at these altitudes in other areas of the range.
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Dates et versions

hal-01126728 , version 1 (06-03-2015)

Identifiants

  • HAL Id : hal-01126728 , version 1

Citer

Salvia García Álvarez, Marie-Claude Bal, Juan M Rubiales, Ignacio García-Amorena, Philippe Allée, et al.. The origin of the open landscapes of the highlands of Gredos (central Spain) during the Holocene: a pedoanthracological approach. 9th European Palaeobotany and Palynology Congress (EPCC), Aug 2014, Padova, Italy. ⟨hal-01126728⟩
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