The Scots pine and silver birch young stands (under 40 years of age) were selected in Central Latvia Lowland in the forest land as well as in afforested agricultural land. Sample trees were selected and the root system was excavated in order to collect empirical material. For the study of carbon (C) content, the root biomass of the selected sample trees was divided in four fractions: coarse roots; small roots, fine roots and stump. The average content of carbon in the root biomass of Scots pine and silver birch differed within ~2.5%. The average content of carbon in Scots pine root biomass in forest land was 48.9 ±0.1% and in afforested abandoned agricultural land it was 49.5 ±0.1%. For birch stands in afforested abandoned agricultural land it is 47.3 ±0.1%. Statistically the average carbon content in root biomass was essentially different among species, land use, different root fractions and age of stands (multifactor variance analysis, p < 0.05). The changes in C content for a single species in different root fractions (stump, coarse roots and small roots) can be attained to the rootwood density characterised by close negative correlation between the wood density and C content in the root biomass. The content of C in root biomass fractions is higher for sample trees with larger diameter dimensions, r = 0.82 (α = 0.05).

Keywords: carbon content, Pinus sylvestris, Betula pendula, forest land, abandoned agricultural land, coarse roots, small roots, fine roots, stump.