Carbon budgets in fertile silver birch (Betula pendula Roth) chronosequence stands

Carbon (C) budgets were compiled for silver birch chronosequence stands by synthesizing the above-and belowground C pools and fluxes with the aim to assess the impact of age on stand C sequestration and cycling. The fine root (d<2 mm) biomass, production, turnover rate and longevity of 13-, 32- and 45-year-old silver birch stands were determined by the ingrowth core method. Fine root production after the third year from the installation of cores was 0.89, 1.44 and 1.31 t ha (1) year (1) in the pole, middle-aged and premature silver birch stands, respectively. Soil respiration (R-s) was measured during the two growing seasons of 2010 and 2011; the trenching method was used to estimate the contribution of heterotrophic respiration (R-h) to total soil respiration. Soil temperature was the driving environmental factor of the temporal variation of R-s and R-h. Stand age affected significantly respiration rates. Annual Rs was 6.2, 9.7 and 8.2 t C ha (1) and annual R-h was 2.97, 4.21 and 3.61 t C ha (1) in the pole, middle-aged and premature silver birch stands, respectively. The annual contribution of R-h to R-s was similar in each stand ranging from 0.43 to 0.48. Total annual net primary production (NPP) of the ecosystems of 7.4, 7.9 and 8.5 t C ha (1) year (1) was estimated in the pole, middle-aged and premature stands. After balancing the C input and output fluxes in the silver birch stands of different development stages, it appeared that they all acted as effective C sinks. Net ecosystem production (NEP) was 4.4, 3.7 and 4.9 t C ha (1) year (1) in the pole, middle-aged and premature stands, respectively. In the premature stand the second layer of the spruce contributed significantly to the increased C input. The annual organic C input into the soil through above-and belowground litter occurred to be of the same magnitude as C loss via annual heterotrophic respiration. Thus, annual increment of woody biomass in fertile silver birch stands reflects annual organic C sequestration in the ecosystem. Among the studied stands, estimated NEP values were the lowest in the middle-aged stand and the highest in the oldest stand, indicating non-linear relationship between stand NEP and stand age. (C) 2015 Elsevier B.V. All rights reserved.