Crown transparency and xylogenesis data for Pinus sylvestris L. and Juniperus communis L.

Prolonged droughts and recurring heatwaves increasingly threaten the functional integrity of mountain forests. Reduced tree vitality and elevated mortality rates are among the most pronounced ecological consequences. In this study, we examined whether different degrees of crown defoliation—categorized as low, medium and high crown transparency (< 35%, 35–70%, > 70%)—influence radial growth dynamics and xylem phenology in two co-occurring conifer species. Field monitoring was conducted during the 2024 growing season (March–October) at a dry-mesic, drought-prone inner-Alpine site on the Mieming Plateau (N47°18.9981′, E10°58.2108′; 959 m a.s.l., Imst District, Tyrol, Austria). We analyzed Pinus sylvestris L. (n = 20) and Juniperus communis L. (n = 20) individuals, using repeated microcoring to assess cambial activity and tracheid formation across xylogenetic phases (cell enlargement, secondary wall thickening, maturation). Microcores were collected at 13 sampling dates for J. communis and 19 dates for P. sylvestris. The number of cambial cells and newly formed tracheids per phenophase were quantified for each sample. In October 2024, increment cores were taken from all individuals to determine tree age and long-term growth trajectories. Sampled P. sylvestris trees were 103–161 years old; J. communis ranged from 27 to 126 years. This dataset provides detailed intra- and inter-annual wood formation records under drought-prone conditions, supporting dendroecological analyses of growth sensitivity to canopy defoliation and climate variability.