Fig. 3.

Distribution of the sampled trees at the treeline in the study site and their height in 2008 (and 2009 for some trees >10 m). The figure also reports the treeline positions over 1700–2000 for 50-year time periods and the treeline and species line (SL) in 2008. The treeline altitude for the 50-year periods ending in 1750, 1800 and 1850 (black-dashed line) was estimated as the average between the 1700 and 1900 treelines since no trees 2 m tall were found in these periods. Potential treelines (grey-dashed lines) PT30 and PT20 were defined by the altitude with more than 100 days per year with a temperature over 5°C over the periods 1975–2004 (30 years) and 1985–2004 (20 years). The orthophoto is courtesy of the Regione Autonoma Valle d’Aosta, Assessorato Territorio, Ambiente e Opere Pubbliche, Edition 2006–Aut. n. 1156 of 28.08.2007