The Effect of Hydrometeorological Factors on Tree Growth (Abies borisii-regis Mattf.) in Mountainous Watersheds (Central Greece)

Tree ring chronologies (tree ring width—TRW, earlywood—EW, latewood—LW) were constructed to investigate fir’s (Abies borisii-regis Mattf.) response to key hydrometeorological factors, namely precipitation, temperature and drought (12-month Standardized Precipitation Evapotranspiration Index, SPEI-12). There has been only one previously published study conducted in the northern area of the species’ expansion (Albania). The current study was conducted in the southern area of the species’ expansion (Central Greece). Precipitation was the most important factor that affected tree growth. May precipitation was positively correlated with LW, while June and July precipitation was positively correlated with both EW and LW. Previous September precipitation was positively correlated with EW and LW. Interestingly, the current September precipitation was negatively correlated with EW. High temperatures in April showed a positive relation with LW, high temperatures in June negatively affected all chronologies, while high temperatures July and August were negatively related with LW. High autumn temperatures in the previous year significantly (negatively) influenced all tree ring chronologies. The SPEI index revealed that wet conditions during May and June positively correlated with high tree growth for both EW and LW, while wet conditions in July and August significantly affect LW formation. Wet conditions in the previous September also had a positive effect on tree growth. SPEI showed similar behavior with precipitation, showing that precipitation is the driving factor in fir growth. The results highlight the importance of summer rainfall and temperature in controlling tree growth in Mediterranean regions. The study revealed significant knowledge on the susceptibility of Abies borisii-regis Mattf. to climate variability and highlighted its consequences for future forest management plans.