Frost rings frequency as indicator of increased frost susceptibility under current warming

Climate change is observed and predicted to have a profound impact on forest ecosystems. Warmer conditions are one of the main drivers of recent increases in productivity and changes in structure and function observed in forests growing in temperature-limited environments. However, the extent of these changes is not homogeneous. With growing seasons lengthening but temperature variability increasing plants remains at risk of frost damage that could negatively affect plant growth. This research aims to investigate the timing and occurrence of frost rings in tree species to get insight on how current warming impacts cold adaptation strategies in trees. In this study, we investigate the sensitivity to frost events in three high altitude tree species Larix decidua Mill., Picea abies L., and Pinus cembra L. We analysed ring width time series of X individuals collected in from two sites in the Eastern Alps (Croda da Lago (BL) and Latemar (BZ) and identified frost rings. By considering daily temperature records, we were able to determine the day in which these frost rings had been formed. Results show that for all the species at both sites, there is a trend of earlier frost ring formation over the last century and a half, shifting from late June in the mid-1800s to mid-May. This shift could confirm the earlier onset and lengthening of cambial activity, increasing the susceptibility time window of trees to frost damage. These findings provide valuable insights into cambial phenology, offering a deeper understanding of how shifting climate patterns influence the timing and activity of tree growth.