Wood anatomy of West European Betula: Quantitative descriptions and applications for routine identification in paleoecological studies

In paleoecological and archaeological studies the species present in wood and charcoal samples are often identified to obtain information about past climatic conditions and vegetation. The main references for identification of Betula at the species level are qualitative descriptions of wood anatomy. The aim of the study presented here was to characterize the wood anatomy of West European Betula species more fully, and quantitatively. For this, the size, abundance, and organization of vessels and rays were quantitatively estimated in carbonized wood samples of four Betula taxa: B. pendula, B. pubescens, B. pubescens ssp. tortuosa, and B. nana. Principal components analyses were used to detect statistical differences among species and to identify characters useful for distinguishing species. An anatomical gradient between B. pendula and B. nana was found, in which B. nana was clearly distinct from the three tree species of Betula. Differences were also observed between the tree species, but with less statistical significance. Our quantitative results support earlier, qualitative descriptions in some respects and conflict with them in others. We highlight the occurrence of narrow vessels in the wood that have not been described previously. This feature accounts for both a major portion of the variance in the data and the discrepancies with earlier qualitative studies. We suggest that B. nana and B. pubescens ssp. tortuosa can be distinguished from one another and from B. pendula and B. pubescens. Based on our results, it is not possible to distinguish between B. pendula and B. pubescens, at least in the routine identification of wood charcoal.