СО₂ fluxes between clear-cut surface and atmosphere in the protective zone of the Central Forest State Nature Biosphere Reserve

Timber harvesting is currently one of the main reasons for the alteration of the natural carbon cycle in forest ecosystems. The evaluation of the related changes in CO₂ fluxes can be complicated by the heterogeneity of vegetation in naturally regrowing clear-cut areas. This study presents the results of experimental measurements of CO₂ fluxes at a clear-cut site in the southwest of the Valdai Upland (European Russia) with herbaceous vegetation and patchy aspen regeneration surrounded by spruce-birch-aspen forest. The measurements of CO₂ flux from soil with herbaceous vegetation were made by the static chamber method. Estimates of total primary production, balance, and CO₂ emissions from undisturbed soils were obtained. The parallel measurements were carried out in various plant communities of the clear-cut area, as well as in a forest stand adjacent to it and similar to the cut one. It is shown that CO₂ emission in the clear-cut was significantly (p = 0.001) higher than in the adjacent forest. For instance, mean daytime midsummer soil CO₂ efflux was 8.3 and 10.7 µmol × m^-2 × s^-1in the forest and clear-cut area, respectively. During three years of observation soil CO₂ efflux in the clear-cut increased from year to year from 6.9 to 12.3 µmol × m^-2 × s^-1. The emission fluxes in the clear-cut site are statistically significantly higher in areas with meadow vegetation compared to areas overgrown with woody vegetation, with median values in the last year 11.5 and 7.5 µmol × m^-2 × s^-1, respectively. The assessment of integration fluxes in the clear-cut area using chamber methods of observation must be carried out considering the heterogeneity of the vegetation cover.