Genetic insights into drought responses of boreal Scots pine

Abstract

Climate change is increasing the frequency and severity of drought in boreal forests, raising concern about the resilience of key tree species such as Scots pine (Pinus sylvestris L.). Understanding tree-level drought responses and their genetic basis is essential for climate-adaptive breeding and management strategies. We assessed drought responses and heritability of drought-response traits in 1,443 Scots pine trees from three progeny trials in southern and central Finland using basal area increment data. Two early-summer droughts in 2019 and 2021 were identified using the Standardized Precipitation–Evapotranspiration Index (SPEI). We quantified resistance, recovery and resilience using a growth-based framework and introduced a novel deviation-from-boundary metric describing departure from the theoretical full resilience in the resistance–recovery plane. Most trees failed to return to pre-drought growth within one year, indicating incomplete short term recovery. Phenotypic correlations between drought-response and growth traits were weak in magnitude (up to 0.24), indicating limited overlap between these trait groups. Genetic-correlation estimates ranged from − 0.72 to 0.63 and were associated with substantial standard errors. Genomic best linear unbiased prediction (GBLUP) models revealed drought response trait heritabilities of 0.03–0.16 in Tuusula and 0.13–0.29 in Hankasalmi. The deviation-from-boundary metric also showed heritable variation, with heritability estimates of 0.03–0.09 in Tuusula and 0.26 in Hankasalmi. Cross-event phenotypic and genetic correlations were weak or imprecise, indicating limited stability across drought events. However, the overlapping 2020 event windows warrant caution. Further validation across independent drought events and sites is needed before these resilience metrics can be considered for operational tree breeding.