Introducing anatomical techniques to subfossil wood

Successful cross-dating of subfossil wood, ideally in combination with precise information on germination and dieback, requires the accurate detection of tree-ring width (TRW) boundaries along continuous measurement tracks from pith to bark. However, wood decay and the mechanical deformation of cells often challenge the dendrochronological analysis and subsequent paleoclimatic and environmental interpretations. Here, we show that wood anatomical techniques can improve the assessment of heavily degraded and/or deformed material. We apply state-of-the-art sample preparation, thin sectioning and double-staining to a unique collection of Late Glacial pines that were growing ∼13,000 years ago in the vicinity of Zurich, Switzerland. Highly resolved anatomical observations not only reveal detailed insights into the quality of each cell, but also allow the extent of wood deformation to be identified. By improving the detection and cross-dating of particularly narrow rings, TRW series might be extended towards the pith and bark, where decomposition and distortion is usually most severe, thus adding to a better understanding of possible germination and dieback processes, respectively. Moreover, thin sectioning has the potential to manually reconstruct original TRWs by correcting for post-mortem deformed ring structures. Our results suggest that anatomical techniques should be routinely applied in the assessment of historical, archaeological and subfossil wood.