Incomplete knowledge of carbon (C) allocation dynamics in trees hinders accurate modeling and future predictions of tree growth. We studied C allocation dynamics in a mature Pinus sylvestris L. dominated forest with a novel analytical approach, allowing the first comparison of: (i) magnitude and δ¹³C of shoot, stem and soil CO₂ fluxes (A_shoot, R_stem and R_soil), (ii) concentration and δ¹³C of compound-specific and/or bulk non-structural carbohydrates (NSCs) in phloem and roots and (iii) growth of stem and fine roots. Results showed a significant effect of phloem NSC concentrations on tracheid growth, and both variables significantly impacted R_stem. Also, concentrations of root NSCs, especially starch, had a significant effect on fine root growth, although no effect of root NSC concentrations or root growth was detected on R_soil. Time series analysis between δ¹³C of A_shoot and δ¹³C of R_stem or δ¹³C of R_soil revealed strengthened C allocation to stem or roots under high C demands. Furthermore, we detected a significant correlation between δ¹³C of R_stem and δ¹³C of phloem sucrose and glucose, but not for starch or water-soluble carbohydrates. Our results indicate the need to include C allocation dynamics into tree growth models. We recommend using compound-specific concentration and δ¹³C analysis to reveal C allocation processes that may not be detected by the conventional approach that utilizes bulk organic matter.