Measuring more – The key to a robust signal in ring-porous earlywood vessel chronologies

Quantitative wood anatomy is a crucial field increasingly used in dendrochronology due to its high intra-ring resolution and close link to ecophysiological processes. However, earlywood vessel chronologies in ring-porous species often show low statistical quality, such as weak common signal strength and low expressed population signal (EPS). This raises questions about whether these limitations are inherent to the wood type or if methodological refinements could improve chronology robustness. This study evaluates how the amount of measured wood per ring (tangential width) and tree replication impacts the statistical quality and reliability of climate-growth relationships. Therefore, we conducted a systematic analysis using a highly replicated dataset (21 trees per site, 45 mm tangential width per tree) from Fraxinus excelsior and Quercus robur as a robust benchmark. We employed advanced image analysis, resampling, and data simulation techniques. Our analyses show that the spread (uncertainty) of obtained climate correlation values increases with lower replication and common signal strength, with replication as the most influential factor, followed by within-tree accuracy linked to the tangential width. We recommend collecting at least two 5-mm cores (8–10 mm TW) per tree and sampling a minimum of 20 trees in environments without a strong limiting factor (low common signal strength). In contrast to common practice, we promote subsampling based on surface quality rather than high correlation with the tree-ring width master chronology and target an EPS ≥ 0.85 for earlywood vessel chronologies. Finally, careful screening within the array of earlywood vessel variables (first row, mean size, different quantiles, etc.) enables to maximize the signal strength. We believe that our approach, results, and recommendations can contribute to improving the robustness of quantitative wood anatomy chronologies in ring-porous species, but likely also in other wood types.