Hydroklimatyczne uwarunkowania przyrostów promieniowych dębu szypułkowego w lasach dolin rzecznych
Authors: Okoński Bernard 
Published: March 2024

The dendrochronological method in dendroecological applications was employed in this study. Ecological transects were established, 3 transects with 30 sampling sites altogether, 5 positions in the valley on the active and passive terrace and an additional position on the plateau, with 1–3 sites in each position. The positions in the valley were selected on the basis of elevation and modelling of the distribution of flooding zones for flood episodes. The turbulent flow approach and the HEC-RAS 4.1 software were applied to model flood zone distribution. A total of 10–15 sample trees were selected on each site (2 core samples were extracted from each tree). Mature trees of the dominant biosocial position, healthy, without mechanical damage, growing in a full to moderate canopy cover were preselected, then random selection of trees was applied. The samples were prepared with standard methods, scanned and tree ring width (TRW) was measured using the CooRecorder software. The measurement quality for each sample TRW series was verified with the CDendro and COFECHA software to correct measurement errors. Series of tree ring width, series of tree ring index (TRI) for standard and residual chronologies were prepared for each site. These series were explanatory variables in dendroecological analysis. Statistical characteristics of site TRW and TRI were calculated to assess site series suitability for dendroecological analysis. Dendroecological analyses were performed as a correlation and response function relationship for the period from 1901 to 2010. The aim of the analysis was to determine the strength and direction of relations between hydroclimatic parameters and tree ring width in pedunculate oak for each site. The explaining variables included monthly precipitation (P), temperature (T), measures of drought (scPDSI, SPEI) and streamflow in the Warta for the Poznan and Nowa Wieś Podgórna gauging stations. Both local and basin-aggregated values of drought indices and precipitation were used. Streamflow data was obtained from the Instuitute of Meteorology and Water Management, the National Research Institute, while the other data was derived from high resolution gridded climatic datasets CRUTS 4.01 (T, P), sc-PDSI Global (scPDSI), SPEIbase v.2.5.3 (SPEI). Cluster analysis was employed to determine agglomeration and similarity patterns for radial growth reactions to hydroclimatic factors (the method using the Euclidean distance as a distance function and complete linkage as the agglomeration method). The zonability of the reaction to hydroclimatic factors affecting radial growth was found in of pedunculate oak growing in the river valley. Two zones may be identified. One comprises less elevated sites located on the active terrace (sites in position 1, 2 and some sites in position 3). The other zone includes sites in positons 4, 5 and some sites in position 3. The radial growth reaction of pedunculate oak to hydroclimatic factors on the less elevated parts of the river valley is weaker than on the more elevated parts. This feature of the relationship is distinct for all of the hydroclimatic parameters employed as explanatory variables, both local and basin-related, including river streamflow. The boundary zone is not well defined, but it is a transitional area, because the sites form position 3 are transitional, being found both in the less elevated zone and the more elevated zone of the valley. The less elevated zone is located 120 to 1500 m from the location of the normal elevation of the Warta riverbank. The variability in the distance is caused by the mosaic pattern of elevation and terrain surface forms in the river valley. The transition belt between the zones is elevated ca. 3 m above the normal elevation of the Warta riverbank. The margin of the first passive terrace (the maximum spatial range of flooding) is elevated ca. 2 m higher than the transition belt between the zones. The hydroclimatic parameters were found not to be the limiting environmental factors of radial tree growth for the less elevated sites in the valley. However, hydroclimatic elements are limiting factors of the radial growth of pedunculate oak for the more elevated sites in the valley. Radial growth response to climatic factors for the sites on the plateau are similar to those for the more elevated sites in the river valley. The relationship between climatic factors and tree ring growth is much stronger for the plateau and more elevated sites in the valley than the relationship for the less elevated sites in the valley. This feature in the relationship is particularly evident both for local and basin drought indices (the r coefficient often exceeds 0.4). Thus the threshold between both zones in the river valley differentiates the areas of different sensitivity of tree growth to drought. The dynamics of the zones identified by different patterns of tree ring growth has a practical dimension. It can be used as an indicator of the spatiotemporal effect of various processes and an impact of anthropogenic activities or the ecological effects of various active protection forms of the forests in river valleys.