In the thesis, 130 years long instrumental records of local temperature, precipitation, and the Dnipro River’s water level in Kyiv have been used to assess the impact of hydro-climatic factors on Q. robur radial growth in floodplain and reference biotopes before and after river regulation. Before the Dnipro River regulation (1965–1977), April–May water level was the main factor which had a positive impact (p>0,05) on tree-ring width and earlywood width in floodplain sites. Q. robur radial growth is limited by lack of precipitation (p>0,05) in reference site. After upstream and downstream dams implementation, the water level influence has become non-significant in floodplain biotopes are located nearby the Dnipro River (p>0,05) and changed to negative (p>0,05) in biotope is separated from the coast by building and divided by the road. The most sensitive ones were pedunculate oak trees, which besides the river regulation, influenced by an anthropogenic change of local hydrology.
The results of the correlation analysis of Q. robur growth-to-climate relationships in the Siverka River and the Petil River floodplain biotope were unexpected. The Siverka River floodplain biotope was influenced by spring floods, which stopped after channel align and dam a river. The positive correlations with May temperature (r=0,37) and negative with June temperature (r=
–0,29) were the main specific Q. robur growth responses before the Siverka River regulation (1950-y). The results have indicated the contrast conditions during vegetation season — the excess water in the period of earlywood formation and the water deficit later in the vegetation season. Since 1977, when a levee downstream of Kyiv was built, the river’s water has been backed up by the mainstream, i.e. the Dnipro River. After river regulation Q. robur growth relation with May-June temperature was non-significant and the main limiting factor was the drought in May (r=0,30).
Drought and water deficit have a greater impact on Q. robur growth in an ecological boundary of its distribution in the steppe. Here oak forests grow in locally humid conditions, such as riverbanks, floodplains and ravines. One of such a steppe azonal forest is Putilovsky forest located in the north of Donetsk city. This stand was part of natural woodland that belonged to the network of riverine and ravine forests of the Kalmius River basin. Positive correlations have been determined between Q. robur growth and May (r=0,20) and April–June (r=0,25) precipitation and negative with April (r=–0,24) and June-July (r=–0,27) temperature. This suggests that favourable Q. robur growth conditions in the steppe are relatively low air temperature and moderate precipitation. The main difference from the Kyiv floodplains biotopes is the negative temperature influence at the beginning of the growth season.
Floodplain forests are the most productive terrestrial ecosystems due to a sustained provision of riverine vegetation with moisture and nutrients. Nevertheless, our results of comparing carbon sequestration in floodplain biotopes and reference site were unpredictable. The reconstruction of carbon sequestration in Q. robur stem has shown that average annual carbon mass is smaller in Kyiv floodplain biotopes compared to an outside floodplain. But both in floodplains and in forests outside it, the Q. robur carbon sequestration ability increases with age. Q. robur trees at the age of 200 and more are capable to maximize carbon sequestration — about 20 kg per year.
The generalized Q. robur tree-rings chronology (1746–2016) reveals broad scientific perspectives in the climatic conditions and extreme floods reconstructions in Kyiv from the middle of the XVIIIth century and the dating of the artefacts of the relevant period. Even greater perspectives open up a continuous chronological series, which can be obtained by combining the generalized chronology from the living Q. robur trees samples and data of archaeological dated wood.
Key words: Quercus robur, tree ring, floodplain forests, hydro-climatic
