Blue intensity, tree-ring dimensions, earlywood vessels and flood rings in floodplain Fraxinus pennsylvanica trees, central Canada

Abstract

Flood rings have been identified in numerous floodplain ring-porous tree species of the genus Fraxinus and Quercus. They are generally characterized by an earlywood having more numerous vessels with smaller cross-sectional area compared to “normal” tree ring. In recent years, blue intensity (BI) has developed as a surrogate method to determine tree-ring density. The method, so far, has been restricted to coniferous species. No studies have assessed the utility of BI in floodplain ring-porous species and its association, among others, with earlywood vessel features and hydrological conditions. In this study, twenty green ash (Fraxinus pennsylvanica Marsh.) trees were analysed. Flood rings were identified with both cross-sectional area of all earlywood vessels ≥ 1000 µm² and BI measured. Results indicated strong associations among given BI, tree-ring dimension, earlywood vessel and flood-ring chronologies. For instance, both earlywood BI (especially EW10BI) and Delta BI (DBI) showed significant inversed associations with earlywood porosity and with flood-ring abundance. These BI parameters were also strongly associated with spring discharge. In green ash, tree rings formed in years leading to flood-ring formation were characterized by increased earlywood density (higher blue intensity caused by an alteration in size and arrangement of earlywood vessels) and, to a lesser extent, by reduced latewood density. The BI features derived from the earlywood and the entire tree ring both prove to effectively complement visual identification of flood ring. Blue intensity in ring-porous species may prove useful in dendrohydrological reconstructions and also in wood sciences, i.e., when estimating tree-ring density is desired. In regards to ring-porous species, further work is warranted comparing software differences in determining BI, evaluating BI signal in other species and from various hydrological regimes.