Common Juniper: a challenge to seek a precipitation signal at high elevation in the Alps

Common juniper (Juniperus communis L.) is by far the most widespread conifer in the world. However, despite its wide distribution, tree-ring research dealing with this species is still scarce. The main reason is likely related to the hardness in crossdating not just comparing different samples, but also within the same plant due to irregular stem shape with strip-bark growth form in the older individuals and to the high number of missing, wedging and false rings. Considering that a precipitation signal is generally missing in the Alpine high-elevation tree species, here we present a pilot study aimed to i) test the dendrochronological potential of common juniper growing above the treeline and ii) verify the precipitation sensitivity of the species. We collected more than 200 samples from three sites in the central and eastern Alps, all between 2100 and 2400 m altitude. As expected, crossdating was exceptionally challenging. However, thanks to the conspicuous number of frost rings acting as pointer years, we were able to successfully date an adequate number of samples to produce a reliable chronology longer than 200 years in all three study sites. Chronology statistics (EPS, rbar, PC1, etc.) were significantly lower than the corresponding values for the high-elevation tree species (larch, stone pine, spruce), but were similar to other species of the same genus found in literature. Climate/growth relationships computed in the last century highlight a significant precipitation signal in winter months, with a high variability among sites that well corresponds to the low spatial dependence of this factor. Despite the difficulties encountered, the possibility of building fairly long chronologies and the likely presence of a significant precipitation signal seems a promising starting point to apply classical dendroclimatological approach on this creeping shrub.