Radial growth response of green alder (Alnus alnobetula) to cold spells: Dendrometer data from the alpine treeline and controlled experiments

Summary

Green alder (Alnus alnobetula (Ehrh.) K. Koch) is a tall, multi-stemmed deciduous shrub widespread in the Central European Alps across the treeline ecotone. We recorded the impact of growing-season cold spells on radial stem growth (RG)–specifically, temporary or complete cessation of cambial activity–under field conditions and in a controlled environment. RG was recorded by dendrometers on mature shoots (15–20 yr old; n=18) at the treeline on Mt. Patscherkofel, Tyrol, Austria (2140–2150 m asl; 47.2086 N, 11.4605 E) during 2023. Additionally, a control and two subsets of juvenile shoots (3–4 yr old; n=5–8 per subset) grown at the botanical garden, Innsbruck, Austria (600 m asl; 47.2678 N, 11.3793 E) were exposed in a climate chamber to cold spells with (i) minimum T_air of -2.2 °C for two days early in the growing season (DOY 162), and (ii) minimum T_air slightly above freezing (+0.87 °C) for six days late in the growing season (DOY 210).