Constellation, le dépôt institutionnel de l'Université du Québec à Chicoutimi

Résumé

Aim : High‐elevation forest line or tree line is an ecological ecotone representing theupper elevation thermal limit for forest development. The current tree line positionis the result of the past human activity interacting with climatic and topographicconditions. In this study, we investigate how climate, local topographic factors andanthropogenic disturbance currently affect tree line distribution.

Location : Apennine Mountains, 900 km latitudinal gradient along the Italian Peninsula.

Methods : Overall, 302 mountain peaks were studied, comprising 3,622 km of mea-sured tree lines. The position of theFagus sylvaticatree line in all peaks wasassessed and correlated with 58 selected variables representing climate, topographyand human disturbance.

Results : The mean tree line elevation was 1,589 m a.s.l., with considerable variabil-ity among peaks. Contrary to our expectations, the tree line elevation was lower inthe warmer southerly exposed slopes compared to north‐facing aspects, where wefound the highest tree line (2,141 m a.s.l.). Correlation analysis indicates that bothclimatic and human density variables are associated with tree line elevation, withthe climate having more influence in high elevation mountains, while human impactplays a prominent role in low elevation mountain peaks. Specifically, we found nega-tive correlations between density of the resident population around each peak andtree line elevation at all examined dates (1861, 1921, and 2011), suggesting a perva-sive negative impact of human activity on tree lines. As regards climatic variables,tree line elevation showed a stronger negative correlation with winter and springmonths temperature than with mean annual temperature. Noteworthy, climatic vari-ables had stronger effect on high elevation peaks (>1,900 m a.s.l.) compared withlow elevation ones (<1,900 m a.s.l.).

Main Conclusion : Our data provide evidence that the current position of theF. syl-vaticatree line in the Apennines is heavily depressed as a result of a complex inter-action between climatic factors and the past human pressure.