The Newfoundland and Labrador Boreal Ecosystem Latitudinal Transect (NL-BELT) is a climosequence of mature balsam fir (Abies balsamifera (L.) Mill.) stands underlain by humo-ferric podzol soils. The transect encompasses multiple regions spanning ~6 degrees of latitude, ranging from southeast Labrador to southwest Newfoundland. Each region contains three, replicated stands with established research plots. All study sites are similar in forest composition, successional stage, and soil moisture, but they differ in mean annual temperature (MAT; 0 to 5.2˚C) and precipitation (MAP; 1074 to 1505 mm). Both MAT and MAP increase with decreasing latitude, analogous to predicted climate change for much of this biome within the next century, and resulting in similar soil moisture regimes along the transect. Soil profiles exhibit thick (in places >20 cm) O horizons, sporadically occurring A horizons, well-expressed E horizons, and B horizons of varying depth to auger refusal. According to growth yield curves established for each region, the ages of dominant trees at each site are all within ~10 years of the age at which site maturity is reached. All sites represent closed-canopy forests at a similar, mature stage of maximum net primary productivity. Harvesting and insect outbreaks are the major mechanisms of stand replacement in each region, with no evidence of fire in any site.