The impact of hydroclimatic conditions on intra-annual increment of raised-bog pines

This study explores the potential of Scots pine (Pinus sylvestris L.) growing in the Čepkeliai raised bog, Lithuania, as a proxy for hydroclimate variability. By adding earlywood (EW) and latewood (LW) measurements to the traditional dendrochronological approach solely based on tree-ring width (TRW) data, we have further parameters for our evaluation of how intra-annual radial tree growth relate to (hydro-)climatic variability. Our results show that EW exhibits higher sensitivity to hydroclimate variables than LW, particularly to shifts in moisture availability. Notably, summer precipitation has a prolonged negative effect on growth, with responses extending up to three years. In contrast, spring (April-May) precipitation enhances ring formation, highlighting the importance of spring water input in nutrient-limited peatland environments. Tree rings also reflect groundwater table (GWT) fluctuations: declining GWT level, indicative of drier conditions, promote growth while increases in GWT linked to higher precipitation tend to reduce radial increment. Temperature further modulates growth dynamics with negative effects of extreme January cold, and positive correlation with previous May and current August temperatures. Our findings underscore the added value of separating EW and LW in dendroclimatic research on peatland pines and confirm their potential as indicators of long-term hydroclimatic variability in peatland environments.