Growing through dry spells: Unveiling tolerance thresholds in three major tree species during soil water scarcity in Central Europe

Le résumé fourni par la source

• Tree species responded differently to short-term dry spells across growth phases. • Beech trees were more drought-resistant than Norway spruce and Scots pine, maintaining stem growth during early and main growth phases. • Scots pine and Norway spruce showed growth reduction after only three consecutive dry days, whereas beech growth declined only in the late phase after seven dry days. • Soil moisture parameters, particularly available soil water (ASW) and soil water potential (SWP), were the main drivers of intra-annual growth variation. • Identifying species-specific soil moisture thresholds can inform adaptive forest management strategies to enhance drought resistance and reduce forest vulnerability under climate change. Rapid climate change profoundly affects global forest ecosystems, though its impact varies regionally and among tree species. In this study, we employed high-temporal-resolution dendrometer data to assess species-specific responses to short-term dry spells in three major Central European tree species—Scots pine ( Pinus sylvestris ), Norway spruce ( Picea abies ), and European beech ( Fagus sylvatica )—across early, main, and late growth phases. We investigated how available soil water (ASW), soil water potential (SWP), and soil temperature (ST) regulate stem radial growth at sub-annual resolution. The soil moisture parameters ASW and SWP were identified as the most important pedoclimatic drivers of growth during short-term dry spells (Consecutive Dry days, CDD; precipitation ≤ 0.1 mm). We evaluated the effects of the timing and duration of dry spells on growth across the early, main, and late growth phases. The short-term dry spells affected trees differently, allowing us to identify the threshold of pedoclimatic variables for the two conifer species and Beech. The two conifer species showed significant stem circumference shrinkage across all growth phases. Significant shrinkage was observed on average after three CDD, with corresponding changes in ASW, SWP, and ST by -4.94 mm, -4.93 kPa, and +0.99 K. Beech, however, maintained growth during the early and main growth phases, reflecting a higher stability during short-term dry spells. Beech responded only to short-term dry spells in the late growth phase, experiencing a significant growth depression after seven CDD, with corresponding changes in ASW, SWP, and ST by -11.70 mm, 30.74 kPa, and 0.60 K, respectively. Our results highlight that late-summer short-term dry spells were particularly critical for conifers and beech, emphasizing the need to integrate soil-climate interactions when assessing intra-annual growth responses and pedoclimatic thresholds. Our findings support the early detection of critical moisture stress levels and provide guidance for adaptive forest management strategies to enhance forest resistance.

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