The rate of carbon accumulation in northern mires largely depends on photosynthetic fixation by Sphagnum mosses. However, estimates of this rate will vary greatly depending on the method chosen to measure their growth. The simultaneous application of the tied thread, geotropic curvature, and brush wire methods was used to assess the differences in their estimates of linear growth and annual production of Sphagnum mosses. The study was carried out within the Koivulambisuo mire system, which is part of the
Kindasovo Research Station of the Karelian Research Centre RAS (southern Karelia). The study examined 7 species of Sphagnum in 25 microcoenoses across 9 sample plots in 3 mire sites. These locations serve as model objects for carbon pool assessment within the national-importance vital innovative project 23-10. In different species, linear increments obtained by the geotropic curvature method were 12.4–144.6 % (12.4–62.4 % – hollow, 66.8–144.6 % – carpet and hummock species) greater than those obtained by the tied thread method, and 51.1–282.3 % (carpet and hummock species) greater than those obtained using the brush wire method. The increment estimation differences between the tied thread and geotropic curvature methods are significantly reduced or even overcompensated when estimating the productivity of different species. In carpet and hummock species, they are significantly reduced, wherefore the productivity determined by the geotropic curvature method is 12.8–40.4 % higher than that obtained by the tied thread method. At the same time, in hollow-dwelling species, productivity determined by the tied thread method is 6.0–17.4 % higher than that estimated by the geotropic curvature method. The brush wire method, applied to plots with carpet and hummock species, has been shown to tend to underestimate productivity relative to the tied thread method (0.95–52.9 %) and geotropic curvature method (40.3–193.2 %). The results presented here were obtained based on one growing season with weather and climatic conditions favorable for the growth of Sphagnum mosses. Further studies will help evaluate how weather and climatic conditions affect the differences between linear growth and production characteristics of Sphagnum mosses estimated by different methods.