DNA of centuries-old timber can reveal its origin

Non-destructive wood identification using X-ray µCT scanning: which resolution do we need?

BACKGROUND

Taxonomic identification of wood specimens provides vital information for a wide variety of academic (e.g. paleoecology, cultural heritage studies) and commercial (e.g. wood trade) purposes. It is generally accomplished through the observation of key anatomical features. Classic methodologies mostly require destructive sub-sampling, which is not always acceptable. X-ray computed micro-tomography (µCT) is a promising non-destructive alternative since it allows a detailed non-invasive visualization of the internal wood structure. There is, however, no standardized approach that determines the required resolution for proper wood identification using X-ray µCT. Here we compared X-ray µCT scans of 17 African wood species at four resolutions (1 µm, 3 µm, 8 µm and 15 µm). The species were selected from the Xylarium of the Royal Museum for Central Africa, Belgium, and represent a wide variety of wood-anatomical features.

RESULTS

For each resolution, we determined which standardized anatomical features can be distinguished or measured, using the anatomical descriptions and microscopic photographs on the Inside Wood Online Database as a reference. We show that small-scale features (e.g. pits and fibres) can be best distinguished at high resolution (especially 1 µm voxel size). In contrast, large-scale features (e.g. vessel porosity or arrangement) can be best observed at low resolution due to a larger field of view. Intermediate resolutions are optimal (especially 3 µm voxel size), allowing recognition of most small- and large-scale features. While the potential for wood identification is thus highest at 3 µm, the scans at 1 µm and 8 µm were successful in more than half of the studied cases, and even the 15 µm resolution showed a high potential for 40% of the samples.

CONCLUSIONS

The results show the potential of X-ray µCT for non-destructive wood identification. Each of the four studied resolutions proved to contain information on the anatomical features and has the potential to lead to an identification. The dataset of 17 scanned species is made available online and serves as the first step towards a reference database of scanned wood species, facilitating and encouraging more systematic use of X-ray µCT for the identification of wood species.

Combining conventional tree-ring measurements with wood anatomy and strontium isotope analyses enables dendroprovenancing at the local scale

Dendroprovenancing provides critical information regarding the origin of wood, allowing further insights into economic exploitation strategies and source regions of timber products. Traditionally, dendroprovenancing relies on pattern-matching of tree rings, but its spatial resolution is limited by the geographical coverage of species-specific chronologies available for crossdating and, in the case of short-distance trades, by scarce environmental variability. Here, we present an approach to provenance timber with high spatial resolution from forested areas that have been exploited intensively throughout history, with the aim to understand the sustainability of the various woodland management practices used to supply timber products. To this end, we combined tree-ring width (TRW), wood anatomical and geochemical analyses in addition to multivariate statistical validation procedures to trace the origin of living oak trees (Quercus robur) sampled in four stands located within a 30-km radius around the city of Limoges (Haute-Vienne, France). We demonstrate that TRW and wood anatomical variables (and in particular cell density) robustly discriminate the eastern from the western site, while failing to trace the origin of trees from the northern and southern sites. Here, strontium isotopic ratios (⁸⁷Sr/⁸⁶Sr) and Ca concentrations identify clusters of trees which could not be identified with TRW or wood anatomy. Ultimately, our study demonstrates that the coupling of wood anatomy with geochemical signatures allows to correctly pinpoint the origin of trees. Given the small geographic scale of our study and the limited differences in elevation and climate between study sites, our results are particularly promising for future dendroprovenancing studies. We thus conclude that the combination of multiple approaches will not only increase the accuracy of dendroprovenancing studies at local scales, but could also be implemented at much larger scales to identify trends in historic timber supply throughout Europe.

How Cultural Heritage Studies Based on Dendrochronology Can Be Improved through Two-Way Communication

A significant part of our cultural heritage consists of wood. Research on historical wooden structures and artefacts thereby provides knowledge of people’s daily lives and the society in which they lived. Dendrochronology is a well-established dating method of wood that can also provide valuable knowledge about climate dynamics, environmental changes, silviculture, and cultural transformations. However, dendrochronology comes with some limitations that end users in cultural heritage sciences must be aware of, otherwise their surveys may not be ultimately performed. We have drawn attention to studies in which dendrochronological results have been misinterpreted, over-interpreted, or not fully utilized. On the other hand, a rigorous dendrochronological survey may not respond to the request of information in practice. To bridge this rigour-relevance gap, this article has considered and reviewed both the dendrochronology’s science-perspective and the practitioner’s and end user’s call for context appropriate studies. The material for this study consists of (i) interviews with researchers in dendrochronology and end users represented by cultural heritage researchers with focus on building conservation and building history in Sweden, and (ii) a review of dendrochronological reports and the literature where results from the reports have been interpreted. From these sources we can conclude that a continuous two-way communication between the dendrochronologists and end users often would have resulted in improved cultural heritage studies. The communication can take place in several steps. Firstly, the design of a sampling plan, which according to the current standard for sampling of cultural materials often is required, is an excellent common starting point for communication. Secondly, the survey reports could be developed with a more extensive general outline of the method and guidance in how to interpret the results. Thirdly, the potential contribution from dendrochronology is often underused, foreseeing historical information on local climate, silviculture, and choice of quality of the wooden resource, as the focus most often is the chronological dating. Finally, the interpretation of the results should consider all the available sources where dendrochronology is one stake for a conciliant conclusion.