Climate Influence on the Expansion and Tree-Ring Growth of Pinus nigra L. at High Altitude in the Central Apennines

Scattered expansion of European black pine (Pinus nigra Arnold) has been observed above the current timberline in the central Apennines. We aimed to detect possible common pattern of structure and growth dynamics of pine regeneration in treeline sites. Over 700 black pine samples growing above the timberline were sampled at four sites in the limestone Apennines of Marche and Abruzzo regions. For each tree we measured basal stem diameter, total height and annual height increments; a wooden core was extracted from the stem near the ground for cambial age determination and detection of intra-annual density fluctuations (IADF). We used multivariate analysis to assess patterns of the main tree structural attributes and dendrochronological analysis for age structure and growth dynamics. Expansion of European black pine started about 35 years ago featuring similar germination peaks, tree structure and growth patterns in all the sites. IADF have similar frequencies and peaks and occur in mid-late summer. These similar patterns occur at all sites besides the local differences and grazing histories suggesting the presence of an overall climate driver.