Historic analogues and species-specific tree growth responses to the 2018-2022 drought sequence in Germany

In recent decades, Central Europe has experienced an increase in the clustering of hot and dry compound extremes, with significant implications for forest health and carbon uptake. The multi-year drought from 2018 to 2022 is a prime example of this, but the severity of persistent drought and its impact on growth likely varies among species and landscapes. Here, we investigate how recent and historical droughts influence radial growth across a hydroclimatic gradient in Germany.

Tree-ring cores were sampled from multiple sites spanning western and eastern Germany to capture contrasts in water availability and elevation. The dataset includes broadleaf and conifer species common in managed and semi-natural forests (Fagus sylvatica, Quercus robur, Q. petraea, Pinus sylvestris, Pseudotsuga menziesii). To quantify drought impact and persistence, we relate growth to multi-timescale drought indices (SPEI) and compare the 2018–2022 sequence against earlier drought episodes. Species-specific growth responses are estimated using a non-linear hierarchical modelling framework (generalized additive mixed models, GAMM) that can simultaneously account for size and age effects, stand context, between-tree variability, and the repeated-measures structure of annual rings.

We present results on (i) how exceptional recent drought persistence is in a historical context, and (ii) which species–site combinations are most sensitive to sustained water limitation, by linking multi-timescale drought metrics to species-specific growth responses across contrasting environments. Our findings reveal that the 2018–2022 period stands out as the most severe multi-year drought event at longer accumulation scales across regions. Meanwhile, growth responses demonstrate pronounced species dependence and site modulation along the gradient. Our work provides valuable insights into recent forest growth anomalies and helps to inform expectations under increasing climate variability.