Drought and cold spells trigger dieback of temperate oak and beech forests in northern Spain

Dieback in temperate forests is understudied, despite this biome predicted to be increasingly affected by more extreme climate events a warmer world. To evaluate the potential drivers of dieback we reconstructed changes radial growth and intrinsic water-use efficiency (iWUE) from stable isotopes tree rings. Particularly, compared size, radial-growth trends, responses (temperature, precipitation, cloudiness, number foggy days) drought, iWUE declining non-declining trees showing contrasting canopy defoliation. This comparison was done six located northern Spain based on three broadleaved species (Quercus robur, Quercus humilis, Fagus sylvatica). Declining presented lower rates than their counterparts tended show variability, but not all sites. The divergence between significant lasted Q. robur (15–30 years) F. sylvatica (5–10 linked summer drought associated atmospheric patterns, wettest sites cold spells contributed decline. In contrast, most responsive terms reduction followed humilis which showed coupled as function vigour. Low higher characterized trees. However, became less efficient close onset, could indicate impending death. forests, decline can triggered extremes such dry spells, amplified warming rising stress.