Late Holocene soil evolution and treeline fluctuations in the Northern Apennines

Abstract

The aim of this study is the reconstruction of Late Holocene soil evolution and environmental changes at the treeline of Northern Apennines (Italy) through field observation, pedoanthracological analysis, soil micromorphology and dendrochronology. Nine soil profiles across the present treeline (c. 1750 m) between 1700 and 2000 m were described. Physical and chemical analyses, and pedoanthracological and micromorphological observations were carried out. Tree ring analysis was also performed to outline recent disturbance events.All soils consisted of two superimposed units. The lowermost unit consisted of a well developed B horizon resulting from intense brunification process, frequently overtopped by a dark Ab horizon. The superficial unit was up to 1 m thick, consisting of colluvium deposits with poorly developed pedogenesis.Below the present treeline, charcoals were observed in the B horizon of the buried soils: Abies and Fagus dominated the anthracological assemblages. Abies charcoals were AMS dated to 790–670 cal BP. Above the treeline, a charcoal assemblage dominated by Abies and Laburnum was found in the buried B horizon. A Laburnum charcoal sample was dated to 3920–3700 cal BP. In the Ab horizon another assemblage dominated by Abies, Laburnum and Vaccinium with abundant insect remains was observed, dated to late Middle Ages.Soil data suggest a recent phase of marked slope instability. Tree ring analysis indicated that this phase occurred at least during the 18th and early 19th century.These analyses, together with previous archaeological evidence, indicate the occurrence of forests well above the present treeline in the Early-Mid Holocene. The lowering of the treeline probably started during Late Holocene, but woody vegetation (open forest or treed heathland) occurred at high altitude until recent times. The colluvial episodes and the burial of paleosols probably took place through successive events during modern times. The dominance or co-dominance of fir at the treeline lasted until historical times. The multi-proxy approach allowed previous archaeological data to be put in a wider context, to give better spatial and temporal extent to treeline fluctuations, and to achieve high resolution for the analysis of the most recent time span.