Dendroclimatic analysis in the Adamello-Presanella Group (Central Italian Alps)

Inter annual or inter decadal climate reconstructions in the subarctic region and in high-mountain environments suffer from the absence of suitable long instrumental climate records. Annual tree-rings, along with other annually resolved natural archives, are widely used as proxies in high resolution paleoclimatology. A temperature signal-loss has been reported in tree-rings width and density records from several temperature-limited environments since the mid-20th century, revealing a decreasing attitude of tree-ring parameters in tracking increasing instrumental temperatures. In this study we carried out a dendroclimatic analysis on a data set of five European larch ring-width chronologies in the Adamello-Presanella Group, in the Italian Central Alps. We intended to evaluate the dendroclimatic potential of the high-elevation conifer vegetation to be used as a climate proxy, assessing the stability over time of the climate/tree-ring growth relationship. The dendroclimatic analysis was performed by means of correlation function and response function analysis, which allowed identifying climate parameters mainly involved in tree-rings growth. For capturing the dynamical variability of climate signal in the five tree-ring width chronologies, and to verify the stability over time of tree-rings/climate relationship, moving correlation function and moving response function analysis have been used. Moreover, to test the efficiency of the tree-rings dataset for climate reconstruction purposes, we conducted a reconstruction of JJ temperature for the 1596-2004 time period. The analysis of climate/tree ring growth relationships, producing results that are consistent with the more recent dendroclimatic studies in the Alpine Region, confirmed the presence of a common climatic signal for conifers living at the timberline ecotone. From the monthly climatic analysis a strong positive influence of early summer (JJ) temperatures on the tree growth emerged, with June mean temperature showing the highest positive correlation. Influence of mean monthly precipitation revealed to be quite irrelevant, although we found that the five chronologies are significantly negatively correlated to June mean precipitation. European larch confirms in this study to be a highly climate-sensitive species, with summer temperature representing the main limitig factor at the treeline. Nevertheless, a temporal instability in growth/climate response is noticeable, that means a general decreasing trend in tree-rings climate sensitivity. Non-stationary relationships with climatic parameters may cause some concerns in tree-ring based reconstructions, which usually presume a stable response of tree-rings to climate change. The reconstruction of 1595-2004 JJ mean temperatures we performed is statistically valuable, but shows higher proficiency in describing high frequency than low frequency early mean summer temperature changes. Overall, a decreasing skill of European larch at the treeline in the Adamello-Presanella Group in tracking increasing instrumental temperatures appears. We also found that extremely warm conditions, such as the heat wave of summer 2003, do not produce a linear response on larch tree-ring growth. Moreover, from the moving correlation analysis emerged a probable effect of a growing season lengthening on larch tree-ring growth