Abstract ID: 3.8821 | Accepted as Poster | Poster | TBA | TBA

Green alder (Alnus alnobetula (Ehrh.) K. Koch) is a tall, multi-stemmed deciduous shrub widespread in the Central European Alps across the treeline ecotone. The focus of this study was to determine key dates of intra-annual radial stem growth (RG) along an elevational transect within the treeline ecotone (1940–2150 m asl). For this purpose, RG was continuously recorded by dendrometers mounted on shoots (n=16–20 dendrometer records per year) at three study plots on Mt. Patscherkofel (2246 m asl) during 2022–2024. The Gompertz function was applied to determine phenological dates of intra-annual RG, i.e., onset, end, duration and time of maximum RG. Results revealed that within the treeline ecotone RG started and ceased around end of June (doy 177±7) and end of August (doy 233±9), respectively. Bud-break was found to occur 28±3 days before the onset of radial stem growth, and leaf shedding was observed to commence in early October. The mean growth duration amounted to 56±9 days, considering all sites and study years. The time of maximum RG was observed in July (doy 192±8), with about 60 % of the annual increment developing during this month. Results of this study revealed that RG of A. alnobetula within the treeline ecotone was limited to a period of only two months, and that the timing of the highest growth rates is not related to photoperiodic constraints. The substantial discrepancy between bud-break and the onset of RG is most likely attributable to the deciduous habit of this tall shrub, indicating that carbon reserves are initially allocated toward leaf development, with cambium activity commencing subsequent to ongoing photosynthesis. The short duration of RG is explained by the clonal propagation strategy, which may trigger an early shift of carbon allocation below ground.
This research was funded by the Austrian Science Fund (FWF), P34706-B.