Wood anatomical traits highlight complex temperature influence on Pinus cembra L. at high elevation in the Eastern Alps

In the context of climate change, scientific community is raising attention on tree response to increasing temperature. In this sense, populations at the edge of their distributional area are crucial to understand the species climate sensitivity. Pinus cembra is of particular interest being a typical high-elevation taxon, spread with mostly scattered populations within its range. Despite its potential, this species is traditionally disregarded by dendrochronological studies because of its low tree-ring variability and climate sensitivity. In this study, we tested the potential of dendroanatomy of this species, analysing time series of xylem anatomical traits of nine trees at the species elevation limit. We measured the mean ring width (MRW) and cell number (CN) per ring. Besides, to improve the time resolution of climate/growth associations, we split each ring in ten sectors, on which we measured the mean lumen area (LA) and both radial and tangential cell-wall thickness (CWTRad and CWTTan). These parameters, assessed on 1.5×106 tracheids, were correlated with monthly and fortnightly climatic data, obtained by the daily climate records over 89 years (1926-2014). The most important factors affecting xylem features were late-spring and summer temperatures. LA and CWT showed a stronger temperature response than MRW, starting from mid-May and early June, respectively. CWT evidenced the longest period of response to temperature, with a significant difference between CWTRad and CWTTan. Analysis of xylem anatomical traits at intra-ring level and the use of daily temperature records proved to be useful for high resolution and detailed climate/growth association inferences in Pinus cembra.