The interplay of tree-ring width, water availability and masting shapes stem wood anatomy in European beech

The decline in stem diameter growth that has been observed in European beech in the recent decades has been attributed to increasing drought as well as masting. Tree-ring width is strongly related to wood anatomy, which constitutes the hydraulic architecture of the tree stem and further relates to wood density and carbon sequestration. While some studies have investigated how wood anatomy responds to drought, little is known about the effects of masting. We sampled 191 (co)dominant European beech trees from 13 stands in southwest Germany by taking thin slices from tree cores. Covering a period 30 years we created time series of tree-ring width and various anatomical variables such as vessel density, relative vessel area and lumen area. Employing generalised additive models we investigated, how anatomy is linked to tree-ring width, and how it is further shaped by drought and masting. Our results show that drought affects primarily the tree-ring width, while only slightly altering anatomical traits – earlywood vessel lumen area and mean hydraulic diameter increase slightly with higher water availability, whereas vessel density and relative vessel area remain largely unaffected. Similarly, masting did not result in substantial changes in wood anatomy – and the most prominent effect was a slightly stronger sensitivity of earlywood vessel lumen area to water availability in mast than non-mast years. Thus, while drought and masting mostly affected productivity overall, any concomitant modifications in wood anatomy are directly linked to a reduction in tree-ring width with little effects beyond these relations.