EVOLUZIONE ALTITUDINALE SPAZIO-TEMPORALE DEGLI ALBERI DURANTE GLI ULTIMI 12000 ANNI IN VALLE D’AOSTA (ITALIA)

Abstract

E. Brugiapaglia, Altitudinal evolution in space and time of trees during the past 12000 years in Aosta Valley (Italy). (IT
ISSN 0394-3356, 2007).
Four sites have been analized, one in a closed forest and three above today’s treeline (Pilaz peat bog at 1900 m a.s.l., Champlong peat
bog at 2320 m a.s.l., Champlong lake at 2300 m a.s.l., and Sant’Anna peat bog at 2304 m a.s.l.) in the eastern Aosta Valley. The results
obtained by pollen, macrofossil data, and 14 radiocarbon dating by AMS, suggest that for periods older than 12000 BP in the analized
sites there was just a herbaceous species and the trees did not reach 1900 m in altitude. Treelimit was at least 400 m lower than today.
Between 12000 and 10700 BP at 1900 m there were rare Betula and Larix. At lower altitudes Pinus increased and the upper treeline
was about 1900 m. Between 10700 and 10000 BP, at 2300 m there were isolated Larix and Betula, whereas at 1900 m there was isolated Betula. This period is characterized by increasing values of herbaceous species-pollen. Between 10000 and 9000 BP at both 2300
m and 1900 m the vegetation made up of Betula and Larix was sparse. Between 9000 and 8000 BP at 1900 m there was a closed forest of Larix and Betula, at 2300 m there was an open forest of Pinus cembra, Pinus sylvestris and Larix, whereas at Sant’Anna at 2300
m in Gressoney Valley, Larix dominated. The treeline was about 200 m higher than today. Between 8000 and 5000 BP at 1900 m there
was a forest with Larix, Abies and Pinus cembra; Pilaz, where Larix dominated, was a contact area between lower subalpine vegetation
of Abies and upper subalpine vegetation of Pinus cembra. At 2300 m, in Champlong, there was an open forest of Betula and Pinus
cembra which was replaced by Larix in drier periods. Larix was dominating in Sant’Anna. Between 5000 and 2500 BP at 1900 m there
were sparse trees of Larix and Abies, whereas at 2300 m there were sparse trees of Pinus, and in Sant’Anna there were sparse Larix
and Pinus cembra. The treeline lowered by about 200-300 m. For the latest period (after 2500 BP) at 1900 m the vegetation was characterized by Larix and Picea, at 2300 m by sparse Pinus cembra and in Sant’Anna by larch. The treeline was influenzed by human
activity which was considerable, as shown by the presence of a village of the bronze age, and the grazing and agricoltural taxa.