Earlywood Vessels in Black Ash (Fraxinus nigra Marsh.) Trees Show Contrasting Sensitivity to Hydroclimate Variables According to Flood Exposure

In recent years, the utility of earlywood vessels anatomical characteristics in identifying and reconstructing hydrological conditions has been fully recognized. In riparian ring-porous species, flood rings have been used to identify discrete flood events, and chronologies developed from cross-sectional lumen areas of earlywood vessels have been used to successfully reconstruct seasonal discharge. In contrast, the utility of the earlywood vessel chronologies in non-riparian habitats has been less compelling. No studies have contrasted within species their earlywood vessel anatomical characteristics, specifically from trees that are inversely exposed to flooding. In this study, earlywood vessel and ring-width chronologies were compared between flooded and non-flooded control Fraxinus nigra trees. The association between chronologies and hydroclimate variables was also assessed. Fraxinus nigra trees from both settings shared similar mean tree-ring width but floodplain trees did produce, on average, thicker earlywood. Vessel chronologies from the floodplain trees generally recorded higher mean sensitivity (standard deviation) and lower autocorrelation than corresponding control chronologies indicating higher year-to-year variations. Principal components analysis (PCA) revealed that control and floodplain chronologies shared little variance indicating habitat-specific signals. At the habitat level, the PCA indicated that vessel characteristics were strongly associated with tree-ring width descriptors in control trees whereas, in floodplain trees, they were decoupled from the width. The most striking difference found between flood exposures related to the chronologies' associations with hydroclimatic variables. Floodplain vessel chronologies were strongly associated with climate variables modulating spring-flood conditions as well as with spring discharge whereas control ones showed weaker and few consistent correlations. Our results illustrated how spring flood conditions modulate earlywood vessel plasticity. In floodplain F. nigra trees, the use of earlywood vessel characteristics could potentially be extended to assess and/or mitigate anthropogenic modifications of hydrological regimes. In absence of major recurring environmental stressors like spring flooding, our results support the idea that the production of continuous earlywood vessel chronologies may be of limited utility in dendroclimatology.

Experimental study and comparative numerical modeling of creep behavior of white oak wood with various distributions of earlywood vessel belt

Many researches have been conducted to investigate creep behavior of wood; however, the effects of structure on wood creep behavior remain unclear. Therefore, the effects of existence and distribution of earlywood vessel belt on creep behavior of white oak (Quercus alba L.) wood were investigated by dynamic thermal mechanical analyzer (DMA) with double cantilever bending in this study. Besides, a comparative numerical modeling simulation on strain curves of white oak specimens was completed using Burger and Five-parameter model. Results revealed that instantaneous strain and 45-min strain of specimens decreased with increase in the distance between earlywood vessel belt and stress acting surface obviously. Additionally, instantaneous strain and 45-min strain of specimens remarkably increased with increase in temperature from 20 to 80 °C. An obvious bending creep behavior was observed with increase in temperature from 20 to 80 °C. Both Burger and Five-parameter model can effectively simulate the creep behavior of white oak specimens with R2 values greater than 0.90. Furthermore, Five-parameter model illustrated a better fitting effect than Burger model in the final creep stage due to the introduction of a non-linear creep strain growth expression. It concluded that creep behavior of white oak wood strongly depends on the existence and distribution of earlywood vessel belt.