Effet des paramètres locaux sur le développement de la végétation dans le Vallon de St. Anna di Vinadio (Alpes Maritimes; Italie)

Abstract

:: Study of the modern pollen rain and comparison of two pollen sequences covering the Late-Glacial and Holocene periods from two sites in the Subalpine belt (Laghi dell’Orgials, 2,130 m, S-W exposition and Lago delle Fate, 2,240 m, E exposition), one on each side of the St. Anna di Vinadio Valley (Italian Maritime Alps), enabled us to place the vegetation succession of this belt in its regional history, highlighting the differences due to physiographic factors and/or human influence. During the Late-Glacial period the two sites were surrounded by Artemisia steppes and located above the timberline formed by pines. Mesophilous deciduous trees (Tilia, Ulmus, and deciduous Quercus) in the lowland are detectable after 12,000 BP. At the transition to the Holocene period, the Artemisia steppes were replaced by grasslands. There were considerable differences between the two sites at the beginning of the Holocene: Betula became important at Fate after 9,700 BP, while the presence of Larix is registered at Orgials before 8,000 BP. High Pinus percentages preceding 9,000 BP must be attributed to transport by wind to both sites. After 9,000 BP a subalpine pine woodland developed at Fate. The development of these pioneer taxa preceded the development of Abies in the mountain belt, which is registered at both sites at 7,820 BP. During the Roman age (1,875 BP), major deforestation occurred, affecting mountain belt fir-woods and subalpine pine-woods and causing forest opening. The increase of Poaceae since this period is a result of the extension of present-day pastures with Nardus stricta.