Climate continentality and treeline species distribution in the Alps

The distribution of tree species and the elevation of the alpine treeline are strongly affected by climate continentality. In the present work we performed a detailed survey of the upper limits of tree vegetation in two areas with contrasting climate located in the central Italian Alps, in order to evaluate the structure of the treeline under different degrees of continentality. Tree and krummholz (stunted) individual position, their dimension and life form were recorded from the upper limit of the closed forest to the species limit. The results were compared with an estimation of tree species distribution at the treeline in the whole Lombardy Alps, performed by a survey of tree species occurrence in areas of known climatic traits. The structure of the treeline (upper limits, life form altitudinal arrangement) and its ongoing dynamics were different in the two areas: climate continentality assessed by hygric and thermal continentality indices influenced the distribution of some treeline species. Although the influence of human and geomorphologic disturbance could not be excluded, the importance of the degree of continentality must be stressed when evaluating the response of the treeline to past and present climatic change.