Adequate sample depth and adequate sample location for two representative individuals per species.

<p>Sample depth values were considered optimal when vessel sampling showed 95 to 100% of significant <i>P</i>-values (Wilcoxon-Mann-Whitney test, <i>P</i><0.05, <i>P</i><0.01, <i>P</i><0.001). The 10 mm wide segment investigated in both study rings was divided into 10 portions according to two radial classes (EE, early earlywood and LE, late earlywood) and to five tangential classes (5×2 mm). In each portion of the segment, <i>P</i>-value percentage calculations were computed on subsets of (a) 10, (b) 20, and (c) 30 vessels.</p

Cambial injury and analysis of earlywood vessels.

<p>Cambial injury occurred during the winter of 2006–2007 and trees were harvested in summer 2010. Earlywood vessels were measured in the injury ring (ir) built during the growing season following wounding and in the control ring laid down the previous year. Tree rings in diffuse-porous species consist almost entirely of earlywood, subdivided here in early earlywood (EE) and late earlywood (LE), whereas latewood (lw) is confined to a very narrow terminal zone mostly made of ground tissue. In both rings, measurements were performed over the whole earlywood within a tangential distance of 10 mm from the wound margin (star).</p

One-way ANOVA results for the eight individuals investigated.

<p>The average vessel lumen area (AVLA), the average vessel lumen diameter (AVLD), and the number of vessels (VN) were calculated in the injury ring built during the growing season following wounding and in the control ring laid down the previous year. Changes (%) in vessel lumen size between the two rings were tested for significance with one-way ANOVA, performed for each tree using the non-averaged lumen area/diameter of all the vessels analyzed.</p

Image_1_Modeled Tracheidograms Disclose Drought Influence on Pinus sylvestris Tree-Rings Structure From Siberian Forest-Steppe.JPEG

<p>Wood formation allows trees to adjust in a changing climate. Understanding what determine its adjustment is crucial to evaluate impacts of climatic changes on trees and forests growth. Despite efforts to characterize wood formation, little is known on its impact on the xylem cellular structure. In this study we apply the Vaganov-Shashkin model to generate synthetic tracheidograms and verify its use to investigate the formation of intra-annual density fluctuations (IADF), one of the most frequent climate tree-ring markers in drought-exposed sites. Results indicate that the model can produce realistic tracheidograms, except for narrow rings (<1 mm), when cambial activity stops due to an excess of drought or a lack of growth vigor. These observations suggest that IADFs are caused by a release of drought limitation to cells formation in the first half of the growing season, but that narrow rings are indicators of an even more extreme and persistent water stress. Taking the example of IADFs formation, this study demonstrated that the Vaganov-Shashkin model is a useful tool to study the climatic impact on tree-ring structures. The ability to produce synthetic tracheidogram represents an unavoidable step to link climate to tree growth and xylem functioning under future scenarios.</p

Image_2_Modeled Tracheidograms Disclose Drought Influence on Pinus sylvestris Tree-Rings Structure From Siberian Forest-Steppe.JPEG

<p>Wood formation allows trees to adjust in a changing climate. Understanding what determine its adjustment is crucial to evaluate impacts of climatic changes on trees and forests growth. Despite efforts to characterize wood formation, little is known on its impact on the xylem cellular structure. In this study we apply the Vaganov-Shashkin model to generate synthetic tracheidograms and verify its use to investigate the formation of intra-annual density fluctuations (IADF), one of the most frequent climate tree-ring markers in drought-exposed sites. Results indicate that the model can produce realistic tracheidograms, except for narrow rings (<1 mm), when cambial activity stops due to an excess of drought or a lack of growth vigor. These observations suggest that IADFs are caused by a release of drought limitation to cells formation in the first half of the growing season, but that narrow rings are indicators of an even more extreme and persistent water stress. Taking the example of IADFs formation, this study demonstrated that the Vaganov-Shashkin model is a useful tool to study the climatic impact on tree-ring structures. The ability to produce synthetic tracheidogram represents an unavoidable step to link climate to tree growth and xylem functioning under future scenarios.</p