Notes on the Larix/Picea wood identification problem: Dendrochronological and wood anatomical insights from a subfossil stem disk

The decades-old problem of distinguishing spruce (Picea sp.) from larch (Larix sp.) wood is still debated in wood identification. Although species-specific anatomical traits have been proposed to address this issue, their variable appearance and limited diagnostic power hinder reliable differentiation, particularly for archaeological wood samples. Finding a stem disk collected over a century ago from a glacial moraine deposit brought us to face the Larix/Picea identification problem again. Here, we skimmed the literature for wood anatomical features typical for each species and examined these traits in the subfossil wood disk. Key features assessed included heartwood and sapwood colour differences, earlywood-to-latewood transitions, tracheid pitting in radial walls, ray tracheid pit borders, the number of epithelial cells per resin canal, and the position of resin canals in rays. Additionally, we measured tree-ring widths to attempt dendrochronological dating of the disk. Tree-ring measurements enabled precise dating and revealed a quasi-decadal occurrence of narrow and light rings, indicative of cyclical larch budmoth (Zeiraphera diniana Gn.) infestations. Based on the presence of these characteristic budmoth rings and successful crossdating with 31 published and unpublished larch chronologies, compared to poor correlation with spruce chronologies, we conclusively identified the disk as Larix decidua Mill. However, our wood anatomical observations did not distinguish between spruce and larch reliably, suggesting that some features may vary with tree age and stem position. This highlights the need for further investigation with targeted sampling of living trees to validate the diagnostic utility of certain anatomical features.