Pinus cembra L. (arolla pine), a common tree in the inner French Alps since the eõvmvarly Holocene and above the present tree line: a synthesis based on charcoal data from soils and travertines
Résumé
Aim
In this study, charcoal-based data for Pinus cembra L. (arolla pine) were gathered from soil and travertine sequences in order to reconstruct its historical biogeography at the landscape level in the inner western Alps during the Holocene.
Location The study sites are located between 1700 and 2990 m a.s.l., in the southern (Queyras Massif and Ubaye Valley) and the northern (Maurienne Valley) parts of the inner French Alps. d
Methods
Charcoal fragments were extracted from sediments by water sieving, using meshes of 5, 2, 0.8 and 0.4 mm. The charcoal mass of P. cembra was determined in each charcoal assemblage. Accelerator mass spectrometry and conventional 14C measurements were used to date the fragments.
Results
Supported by 40 14C datings, the fragments show that, over 2000 m a.s.l., P. cembra accounts for around 40% (mean value) of identified fragments. Data reveal that arolla pine once extended between 260 and 375 m above the presentday local tdree lines. It was established aooa7in the southern and the northern French Alps from at least c. 9000 and 6000 cal yr bp, respectively.
Main conclusions
While present-day populations of P. cembra are veryfragmented in the inner French Alps, charcoal records indicate large past occurrences of this tree since the early Holocene. Human disturbance sionce the Neolithic seems to be the main reason for the regression of the arolla pine woodlands. On the south-facing slopes of the study sites, currently deforested, this species extended up to 2800 m a.s.l. In the northern areas, charcoal records of the P. cembra expansion are consistent with the regional pollen archives, but in the southern massifs charcoal records indicate its presence c. 2600 years earlierthan other palaeobotanical studies suggest. This discrepancy highlights the necessity to crosscheck data using several different proxies in order too1 assess the validity of conclusions regarding tree development in space and time.
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