The article presents the results of long-term (10 to 38 years) studies on the productivity dynamics in 11 widespread Sphagnum moss species: Sphagnum balticum, S. centrale, S. divinum, S. fallax, S. fuscum, S. majus, S. obtusum, S. papillosum, S. riparium, S. subsecundum, S. warnstorfii in mid-boreal mires of Karelia. Three groups of species were distinguished based on averaged annual productivity levels: 1 – the highest productivity, found in Sphagnum riparium (11 g/dm²), which grows in inundated swampy habitats and does not tolerate drying out; 2 – average productivity in S. fallax (6 g/dm²), S. majus (6 g/dm²), S. obtusum (5 g/dm²), S. balticum (5 g/dm²), S. warnstorfii (5 g/dm²), and S. subsecundum (4 g/dm²), which grow in low-flow flarks, hollows, and on carpets; 3 – the lowest annual productivity in S. centrale (2.5 g/dm²), S. papillosum (1 g/dm²), S. fuscum (1 g/dm²), and S. divinum (0.8 g/dm²), which grow on ridges and low hummocks with abrupt moisture fluctuations. The productivity of Sphagnum moss cenopopulations is predicated primarily on the habitat moisture patterns, as well as on the species’ biological features and the cenopopulation density. Regression analysis of the relationship between July-August precipitation volumes and Sphagnum moss productivity showed a lack of significant correlation for a number of species. Only four species (S. obtusum, S. centrale, S. fallax, S. papillosum) exhibited a positive correlation between their productivity and precipitation volumes in these months. When the mire water table rose in the summer seasons with abundant precipitation, hydrophilic Sphagnum mosses demonstrated higher productivity.