A juniper tree-ring network across the Alpine range

Common juniper (Juniperus communis L.) is one of the most widespread conifer in the northern hemisphere but even if it has been proved to be sensitive to climate, it is still not widely used for dendrochronological purposes. This is likely due to the crossdating difficulties related to the irregular growth form and the high frequency of erratic and outer missing rings. Nonetheless, we selected this creeping shrub to create a network across the Alps in order to i) check the presence and consistency of the climatic signal in its tree-ring width series, and ii) compare its tree-ring pattern with climatic data and with the tree-ring patterns of trees species growing at similar altitudes. We selected seven sites in the whole Alpine range (44°37’- 46°45’ N, 7°05’- 13°27’ E) from 1800 to 2400 m altitude, where we sampled almost 300 junipers and 250 trees. On all sites we were able to successfully build chronologies longer than 150 years. Juniper growth has been proved to be consistently negatively correlated to winter precipitation, i.e. to snow cover. On the contrary, tree growth showed positive correlations with summer temperatures but no winter precipitation association. Comparing both chronologies of shrubs and trees and their responses to climate, we found an evident decupling between the two growth forms: shrubs seem more sensitive to snow accumulation and soil conditions, while trees are more coupled to the atmosphere and air temperatures. This work highlights the potential of common juniper as a valuable natural archive. Its winter precipitation sensitivity, well documented across the whole alpine range can be considered a good starting point for a potential reconstruction of past winter precipitation or snow accumulation in this region.