Root ingrowth cores were used to quantify fine root response to nutrient treatments in early and late successional stage black spruce-feathermoss ecosystems that originated from either fire or timber harvesting [cut with protection of regeneration and soils (CPRS)]. Three nutrient treatments (nitrogen, phosphorus, and calcium) were added to ingrowth cores, and root ingrowth was compared with control (water-treated) cores. The efficacy of using a natural substrate from the black spruce-feathermoss organic horizon with the ingrowth core technique was also evaluated. There was an important effect (p = 0.06) of nutrient treatment on fine root length and biomass in the cores, and the age of the stand since the time of the disturbance helped to explain differences in root lengths and biomass (p = 0.05), with older sites having greater root length and root biomass ingrowth into the cores during the study period. Experience with this technique demonstrated that the choice of fill material, core preparation, and the role of mycorrhizae in root proliferation and nutrient export from the cores are important to consider in future use of this technique. © Taylor & Francis, Inc.