Biomass production and carbon sequestration in a fertile silver birch (Betula pendula Roth) forest chronosequence

During recent decades, studies of the carbon (C) balance of forest ecosystems have became more actual, mainly in connection with the global increase of CO2 in the atmosphere. In the present study the stand chronosequence approach was applied to analyse C sequestration dynamics. Study was made of C accumulation both in biomass and in the soil in 6-60-year-old silver birch (Betula pendula) stands growing at fertile (Oxalis) sites. As the growth of the studied stands was vigorous, their yield was higher than that presented in several yield tables for earlier periods. The C concentration (C%) in different compartments of the trees varied between 47% and 55%. However, the weighted average of C concentration in the silver birch trees was approximately 50% regardless of stand age. The average C concentration of the herbaceous understorey plants was 43.3 +/- 0.5%. The soil C-org pool was independent of stand age, and so far there occurred no C accumulation during stand succession, expressed as C-org values or stage of forest floor formation. This might indicate fast C-org turnover in the soils of the Oxalis site. The total C pool in a mature silver birch stand was 185 t ha(-1) of which 50% was accumulated in the aboveground part of the trees. In young birch stands the C pool in aboveground biomass and in the soil accounted for 21-39% and 53-71%, respectively, of the total C pool of a stand. In pre-mature and mature stands the corresponding share accounted for 50-59% of the aboveground C of the trees and 29-38% of the soil C pool. Due to closed canopies, the role of herbaceous understorey plants as a C sink was modest, constituting 1% or even less of the total C pool of the older stands. The annual C flux 1.6 t ha(-1) yr(-1) into the soil via litter fall was the largest in the middle-age stand. Our results show that the main C sink in fertile silver birch stands is located in the wooden parts of trees. The C pool in tree biomass increased with stand age, whereas the soil C-org pool remained stable. For a more profound understanding of C cycling in silver birch forest, soil respiration fluxes should be measured. (C) 2011 Elsevier B.V. All rights reserved.