Fire is the most prevalent form of stand-replacing natural disturbance in boreal forests. However, corresponding with increasing global resource demand, harvesting now affects millions of ha of boreal forest each year, yet our understanding of harvesting impacts on boreal carbon (C) dynamics relative to fire remains debated. Although lot of work has been done to quantify and model boreal forest C dynamics, several knowledge caps remain. For example, pools like dead roots, medium and fine roots and stumps are rarely studied. Also, there are only few studies reporting total ecosystem C and there is no clear understanding of the primary processes. This thesis looks how anthropogenic and natural disturbances (clearcutting and wildfire) influence forest ecosystem C balance. Thesis consists of four articles. First is a literature review of boreal forest C dynamics. Second is a study about the aboveground biomass C dynamics. Third paper reports dead wood densities in the area so that collected dead wood volume data could be converted to dead wood mass estimates. Fourth paper combines all relevant C pools and looks at the total ecosystem C dynamics in young boreal forests. Result is a direct comparison of C stocks following clear-cut harvesting and fire over a 27-year chronosequence in the boreal forest of central Canada. While many past studies have lacked complete measurement of all C pools, this thesis provides full coverage of all C pools, including live biomass, deadwood, forest floor and mineral soil. Results indicate that there is no significant difference in overall ecosystem C stocks during early stand development, but that the relative contribution of C pools to total forest ecosystem C varies between disturbance types. Live biomass C was significantly higher following harvesting compared with post-fire stands, because of residual live trees and advanced regeneration left intact during harvest. On the contrary, most live biomass was killed following intense crown fire and therefore post-fire stands contained higher stocks of deadwood C. Snag and stump C mass peaked immediately following fire, but dramatically decreased 8 years after fire as dead trees began to fall over, contributing to the downed dead wood C pool. Contrary, snag and stump C mass increased after logging. Although the thesis did not show the initial decrease in forest floor C mass commonly acknowledged directly after stand-replacing disturbance, forest floor C stock steadily increased over time. C amount in mineral soil did not change after harvest but increased after fire. Therefore, current management practices (i.e. harvesting and planting or seeding) in boreal mixedwood forests of central Canada have no negative impact on total ecosystem carbon. Considering also the life cycle of products made from this wood and the displacement effect (i.e. use of wood instead of concrete or steel that have higher C footprint), shows that harvesting results an increased C uptake from the atmosphere, therefore moderating climate change. For better comparison of disturbance effects it is necessary also to compare C dynamics in older forest. Boreaalne mets sisaldab hulgaliselt süsinikku ja mängib seetõttu globaalses süsinikuringluses olulist rolli. Muutused boreaalse metsa süsinikuringes avaldavad mõju ka globaalsele kliimale. Ajalooliselt on olnud tuli Põhja-Ameerika boreaalse metsa ökosüsteemi protsesside peamine mõjutaja. Üha suurenenud vajadus metsa bioproduktsiooni kasutamiseks on muutnud metsaraied olulise tähtsusega häiringuteguriks. Kuigi palju tööd on tehtud boreaalse metsa süsinikuvoogude kvantifitseerimisega ja modelleerimisega, on teadmistes mitmeid olulisi lünki (näiteks: surnud juurte mass, peen- (