Effects of soil parameters on radial stem growth of four spruce stands in Austria

Understanding tree growth in relation to environmental conditions is essential, particularly in the context of climate change, where rising temperatures, frequent droughts, and disturbances threaten forest health and productivity. This study analyzes high-resolution data from four intensively monitored Picea abies stands in Austria (2010–2020), where dendrometers recorded hourly stem increments on 10 trees per site. These measurements enable a detailed analysis of growth responses to environmental changes. The data were collected as part of the ICP Forests and LTER monitoring initiatives. In this study, we tested different generalized additive mixed models (GAMs) to evaluate various energy and moisture-indicating parameters derived from on-site measurements, aiming to determine which input parameters best model tree growth. The best model consisted of combinations of soil moisture (SM) and soil temperature (ST) data. Furthermore we analysed how the relationships established differ for three different times during the growing season. We found that high SM consistently had a positive effect on tree growth, wheras the effect of ST varied depending on the timing. Our findings underscore the importance of monitoring soil conditions, particularly for species like Picea abies , which are known for their sensitivity to environmental changes due to their shallow rooting systems and vulnerability to drought.