Are young trees suitable for climate-growth analysis? A trial with Pinus nigra in the central Apennines treeline

n the context of ecological research, tree-ring analysis often deals with short time series (< 30 years). Theircrossdating and averaging can be difficult but crucial to use such data for ecological modelling, multivariatestatistics, and climate-growth analysis. Several studies were conducted in the Central Apennines (Italy) on recentencroachment of European black pine (Pinus nigraJ.F. Arnold) on treeless areas above the current forestline.Growth of young trees is mainly controlled by endogenous or microclimatic factors making usual den-drochronology methods less applicable and crossdating very difficult or even impossible. The potential ecolo-gical information deriving from tree-ring growth in short series is therefore limited by this methodological bias.The aim of this study is to test suitable methods for optimizing the use of short ring series for further analyticaluse. A dataset of 734 tree-ring series of young European black pines (mean cambial age 15 years) growing athigh altitude in 8 sites was used in this analysis. At each site tree-ring series were divided in two groups based oninter-series correlation: the crossdated or selected series (SEL), and non-crossdated or rejected ones (REJ). Thefollowing dendrochronological parameters were calculated for SEL and REJ series: mean tree-ring width, meansensitivity, Gini coefficient,first order autocorrelation, inter-series correlation, andGleichläufigkeit(GLK). Twomethods of pointer years analysis were tested in order to detect years with synchronous growth: i) Normalizationin a moving Window (NW) and ii) the RElative growth change method (RE). The two methods were applied tothe raw series varying the standard thresholds, in order to detect synchronous growth-years in SEL and REJgroup. A sensitivity analysis was included to assess how the threshold choice in the analysis could affect theresults obtained. The term“common”was used to indicate years with similar tree growth response. Differencesin the detected number of common years within SEL and REJ were obtained using different time windows withthe RE and NW methods. The 47 % of all series were classified as SEL, showing more common years than the REJseries. However, a similar result occurred considering all the series together without SEL/REJ discrimination. Ingeneral, a significant occurrence of common years could be a tool to select series to be averaged for a site meanchronology. These are preliminary but encouraging results contributing to a more efficient use of the ecologicalinformation provided by short time series from young trees.