Total Carbon stock, and trees Carbon source or sink flux in Finnish forests since 1921

The content of elementary Carbon in the dry biomass is quite constant of 50 per cent, of the dry weight. In simplified calculations this percentage can be used for the dry biomass of trees, for the dry biomass of grasses and cereals as well as the for the young humus in the soil. The coefficient for trees, Carbon multiplier (CM) for calculations of Carbon from solid cubic meters, can be calculated in a similar manner as the calculation of dry biomass multiplier.


Picture 1. Abundant Carbon stock in the Scots pine forest, Kuusamo


Also in the total forest growing Carbon stock, it is logical to sum the stems, the branches including the foliage, and the roots. Mathematically the solid cubic meters in the stems (s, cubic meters) can be converted into total Carbon stock (c, tons C) with a coefficient or carbon multiplier (CM).

(1)     c = CM * s

 Calculated as average from the Finnish forest inventories VMI 11 and VMI 12 the Carbon Multiplier is

(2)     CM = 0.35314 tn C/m3

 Using the Carbon Multiplier with the dataset of solid cubic meters in Finland, the development of Carbon stock in forest trees is shown in Figure 1. By shape it is similar to the Solid cubic meters in the forest trees (stems).





Figure 1. Amount of elementary Carbon, the Carbon stock in Finnish forests since 1921, in million tons of C.




The coefficients of the 2nd degree polynomial regression equation

(3)     c = A * t^2 + B * t + C

 are

 A = 0.063439
B = -245.86
C = 238691

 (c = elementary Carbon in mill. tn, t = year, t^2 =  t squared)

 The regression, R-squared value is 0.98544. It is the same as for solid cubic meters and for dry biomass.

 By derivating the Carbon equation, the 2nd degree polynomial equation, we get the annual change of Finnish Carbon stock in the forests, the Carbon flux

(4)     dc/dt = 2A * t + B

 When dc/dt is negative, we talk about Carbon source flux or Carbon emissions flux. When dc/dt is positive we talk about Carbon sink flux (Figure 2).


Figure 2. Carbon source flux (before 1939) and Carbon sink flux in Finnish forests (stems, branches including foliage) since 1921.




The forests of Finland caused a Carbon source flux (Carbon emissions flux) in early times, until (calculated) year 1939. After that there has been a continuous, even increasing Carbon sink flux into Finnish forests.

 In 2020 the calculated Carbon sink flux into Finnish forests is 10.436 million tons of Carbon. In the latest national forest inventory the land area of forests in Finland is 26.215 million hectares. Calculated from the above approach, the average Carbon sink flux into a Finnish forest hectare in year 2020 is at level of 393 kg C/ha/a.

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