Pilot study on the effect of slope aspect on growth dynamics and drought response of Norway spruce (Picea abies [L.] H. Karst.) in low-elevation temperate forests

In general, slope aspect modifies the phenology and growth dynamics of trees in temperate forests of Central Europe. This study investigates radial growth dynamics and phenology of Norway spruce (Picea abies [L.] H. Karst.) in two forest stands with contrasting slope aspect (north vs. south) located in low-elevation temperate zones. Using automatic dendrometers, stem diameter variations and growth phenology were monitored throughout the 2025 growing season, complemented by continuous measurements of volumetric soil moisture. Pilot results indicate that trees on north aspect slope initiated growth earlier, maintained a longer growing season, and achieved greater radial increments compared to those on south aspect slope. The factor of this differential growth response was probably higher soil water availability on northern aspects, which buffered the effects of summer drought. The findings highlight the importance of microclimatic conditions (temperature, available soil moisture, and soil properties) shaped by topography in regulating the phenology and growth dynamics of Norway spruce. They further suggest that north-facing slopes may hypothetically serve as microclimatic refugia for the Norway spruce cultivation at lower elevations under climate-change conditions. However, the local and pilot nature of this study limits the extent to which broader generalizations can be made.