Dynamics of carbon stock in the stand of Pinetum andromedo-eriophoroso-sphagnum over 50 years under extensive drainage in the conditions of the subtaiga of European Russia (West Dvina Peatland-Forest Station)

In 1972-1973, large-scale drainage of peat lands for the purposes of effective forestry was carried out on the territory of the West Dvina Peatland-Forest Station of the Institute of Forest Science of the Russian Academy of Sciences in the Tver Region [Biogeocenological ..., 1982]. Here, in the conditions of the subtaiga of European Russia, swamp forests, bog moss forest and swamps are common, formed on different types of peat − from eutrophic to oligotrophic.

In 1974, a permanent sample plot was laid in the Pinetum andromedo-eriophoroso-sphagnosum on the oligotrophic bog. Repeated surveys of this sample plot were conducted in 1983 and 2023. The sample plot (SP) has the number 5-74, has an area of 0.36 ha and a rectangular shape of 36×100 m² (Fig. 1). The long side of the SP is located parallel to the drainage ditches 35 m from them. The distance between the ditches is 106 m. The depth of the peat is about 4 m. The drainage regime corresponding to the location of SP 5-74 in the middle of the 106-meter channel is considered extensive.

The peat soil was characterized by the constancy of the botanical composition of peat-forming agents up to 3.5 m and was represented by the upper magellanicum peat (Sphagnum magellanicum Brid.) with a degree of decomposition of 5-25%, deeper − sphagnum transition (Sph. girgensonii Russ.) with a decomposition rate of up to 30%. The carbon content in peat is 48-50%, the pH does not exceed 3.0, the ash content is 2-5%. High peat soil is characterized by a low volume mass (density): from 0.046 in the upper layers to 0.090 g/cm³ in the lower ones [Glukhova, 1990].

In 1974 SP 5-74 was laid in the Pinetum andromedo-eriophoroso-sphagnosum, which was characterized by Vb class of productivity and V class of age. In 1983, a more productive pine forest of the same V class of age was formed at this place, but still belonging to the Vb class of productivity: compare table 1 for 1983 M = 24.4 m³/ha, and for 1974 M =14.3 m³/ha. In 2023, the Pinetum ledoso-sphagnosum drained of the Va class of productivity and V class of age with M=50.0 m³/ha was already described at this site. The taxational characteristics of the stand by year and layer are given in table 1.

Extensive drainage of Pinetum andromedo-eriophoroso-sphagnosum with Vb productivity class showed that 10 years after drainage, a more productive pine forest was formed, and 50 years later – Pinetum ledoso-sphagnosum drained with Va productivity class. Based on the taxation data, the stock of stand was calculated for three years of observations (1974, 1983, 2023), which amounted to 14.3, 24.4 and 50.0 m³/ha, respectively. To convert stand stocks into carbon stocks in the phytomass of a stand (trunk, branches, foliage, roots), a conversion coefficient was used, which, in accordance with the methodological guidelines [On approval ..., 2022] turned out to be 0.314. The analysis of carbon stocks showed that it increased 1.7 times in 10 years, and 3.5 times in 50 years.

Regression analysis of these data showed a linear dependence of the carbon stock (C) on the age of extensive drainage (A_drain) over a 50-year period (Fig. 2):

C = 0.2322 × A_drain + 5.0116, t/ha,

where R² = 0.99; p-value (F) = 0.064 for α = 0.05.

The coefficient of determination (R²) of the regression linear equation is high, but the equation is not reliable (p-value (F) > α). In the future, these data can be replenished by analyzing the increments of model trees or mathematical modeling.

Over the 50-year drainage period, the average annual increase in the stock of the stand was 0.71 m³/ha and the average annual increase in the carbon stock of the phytomass of the stand was 0.24 t/ha. An analysis of the literature on drained bog pine forests of the V-Vb bonitet showed that the stock of stands, depending on the age of drainage, may generally increase, less often decrease.