Floodplain forests are highly productive terrestrial ecosystems that perform crucial ecological functions, e.g. carbon sequestration. Quercus robur, a long-lived hardwood species often dominating in floodplains, is an appropriate object to investigate the long-term aboveground carbon fixation. In this study we apply dendrochronological approaches for reconstruction of the carbon sequestration in Q. robur stem biomass. We studied trees growing in five floodplain sites in Kyiv and compared them with a site situated about 4 km away from the nearest floodplain, Feofania Park. The total carbon stock in stems of Q. robur at the age of 50 years averages 319 kg in the Muromets forest, 129 kg in Zhukiv Ostriv Reserve (zakaznyk), 114 kg in Lisnyky Reserve (zakaznyk), 101 kg and 72 kg in the Bychok and Dubysche forests, respectively. At the age of 150, oaks growing in the Zhukiv Ostriv Reserve show the largest amount of stems carbon, 902 kg, while in Lisnyky Reserve trees contain the lowest value of 708 kg. Long-term estimation reveals an increasing trend in the annual carbon stock in all studied floodplain forests, although the highest values up to 15 kg per year are found to occur in periods with optimal growth conditions. In the periods of drought and low water level of the Dnipro River, floodplain oaks yearly carbon stock is found to drop to 9 kg. At the same time, carbon accumulated in old -grown oaks outside the floodplain is higher than in the floodplain forests by 37% at the age of 25 and by 14–28% in older trees. In the Muromets site, 25 year old oaks are found to have 56% higher carbon accumulation than in the trees of the same age in Feofania. Hence, this difference becomes non significant with trees aging. The analyses using 25-yr successive intervals reveal that carbon stock in Feofania is higher than that in the floodplain by 1.6 and 1.5–2.8 times in young and in mature trees, respectively.
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