Root System Architecture of Scots Pine as an Ecological Indicator of Site Productivity: First Insights from Multichannel Ground-Penetrating Radar

Tree root-system architecture is vital for forest resilience under rising climate stress, yet techniques like excavation are destructive, slow, and unsuitable for large surveys. We evaluated how Scots pine (Pinus sylvestris) root architecture varies across contrasting environments using non-invasive, high-resolution multichannel ground-penetrating radar (GPR). Plots in the Olkusz Forest District (southern Poland) spanned gradients of soil fertility and stand age. A multichannel radar array produced 3D subsurface volumes, from which two traits were derived: the 2D planar root extent and the 3D rooting-envelope volume. Generalized additive models linked these metrics to site, stand, and tree characteristics. Multichannel GPR revealed clear site-driven differences in root structure and delivered markedly better data quality than single-channel systems. Selective excavation of visible roots confirmed close agreement between radar estimates and true root positions. Root architecture shifted along the fertility gradient and depended strongly on tree size, stand density, and age: rooting volume increased with site productivity and diameter at breast height but declined with stand age and relative spacing. Overall, Scots pine shows strong adaptive plasticity, and multichannel GPR provides a powerful way to integrate below-ground traits into monitoring, modeling, and climate-smart forest management.