Abstract ID: 3.8768 | Accepted as Poster | Poster | TBA | TBA

Drought is increasingly impacting forests, even in mountainous regions. The Matsch valley, one of the driest areas in South-Tirol, may serve as a model for future conditions in broader Alpine regions. Xylogenetic analysis can assess the precise impact of climate on wood formation. This study aims to understand the relationship between xylem formation and environmental factors to predict the effect of climate change on tree growth. To this end, we sampled four plots along an elevation transect, including four species and 40 trees in total: 20 Larix decidua Mill., 10 Pinus cembra L., 5 Pinus nigra Arnold, and 5 Picea abies L. .These were distributed as follow: 1070 (F1, low elevation), 1715 (F2, mid- elevation), 2100 (F5, high elevation) and 2250 (FL, forest line) meters during the 2023 and 2024 growing seasons. Based on temperature alone, we would expect growing season length – defined as the difference between the start of the enlarging phase and the end of the secondary cell wall thickening-to decrease with increasing elevation. However, lower elevations may experience drought-induced premature growth cessation. We also expected deciduous larch begin growing later than the evergreen spruce or pines as it must first leaf out before growth. Preliminary results from 2023 support these hypotheses. At F1 and F5, larches exhibited a 135-day growing season, though their start and end dates differed by 20 days. Surprisingly, at F2 – where growth was expected to continue longer than at F5 and FL-the growing season ended earlier, suggesting that drought impacts extend up to 1700 m. As expected, the shortest growing season was observed at FL, mainly due to a delayed start of cell enlargement. Pines initiated growth earlier than larches at all sites. However, in F2,the onset difference between larch and spruce was only two days. Black pine has the longest growing season, while Swiss stone pine at FL had the shortest. Across all sites, the start of the growing season showed less variability than its end. To validate these preliminary findings, we conducted a second xylogenesis campaign in 2024 and we will correlate our results with dendrometers, sap flow and wood anatomy data.