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• Multichannel GPR is a promising tool for analyzing root system architecture. • GPR enables detailed detection and spatial reconstruction of lateral root characteristics. • Root system depth and length vary with soil type, stand age, and stand density. • Root system depth and length measured with GPR do not differ significantly from field measurements. Understanding the structure and variability of tree root systems is essential for assessing forest resilience under increasing climate stress. Despite their ecological significance, roots remain among the least studied components of forest ecosystems due to the limitations of traditional, invasive measurement methods. In this study, we present the first application of multichannel ground-penetrating radar (GPR) to assess the variability of root system architecture in Scots pine ( Pinus sylvestris ) stands across contrasting site conditions and developmental stand stages. Using the Stream C radar system (IDS Georadar), we conducted high-resolution 3D root mapping on 27 trees. A total of 294 roots were detected, enabling the calculation of key traits including total root number, maximum rooting depth, and average root length. Ground-truth validation through selective root excavation confirmed a high degree of correspondence between predicted and actual root positions. Root system variability was analyzed using Generalized Additive Models (GAMs), which revealed strong, non-linear effects of stand age, tree diameter (DBH), stand density (RSI), and soil type on root development. Our findings demonstrate that younger trees growing on poor, sandy soils tend to develop shallow, laterally extensive root systems, while older trees on more fertile sites exhibit deeper rooting. These preliminary patterns may offer new perspectives compared to classical excavation-based studies and highlight potential influences of both ontogeny and site characteristics on belowground structure. The successful application of multichannel GPR highlights its value as a non-invasive tool for root system assessment at ecologically meaningful scales. This approach offers new opportunities to monitor belowground responses to environmental stress and to support adaptive forest management in a changing climate.