Radial growth-based assessment of sites effects on pedunculate and greyish oak in southern Romania.

This study focuses on the climate growth drivers of Quercus robur L. (pedunculate oak) and Q. robur subsp. pedunculiflora K. Koch. (greyish oak), occurring in the biodiversity of three sites in southern Romania. We determined the degree of tolerance of the greyish oak, between the tardive and praecox varieties, to environmental stress, between 1951 and 2016. Total tree ring-width (RW), and earlywood (EW) and latewood (LW) measurements were subject of periodical and monthly climate-growth analysis. Our results revealed a moderate relationship between climate and tree-growth. A significant and positive relationship was observed between RW and previous growing season precipitation. Mean and minimum temperatures affected both positive and negative tree-rings during the growing season. We also observed that winter and spring represent key seasons for differentiating tardive from praecox varieties, affecting the intra-annual variability of ring-width, and EW and LW parameters. The correlation between the tree-ring measurements and daily climate data shows a clear offset of the starting growth between greyish oak varieties. A weak influence of stressors on tree-growth at the sites was observed through pointer year and resilience components analysis.