A synoptic view on intra-annual density fluctuations in Abies alba

Abstract Tree growth, as an archive of environmental conditions, has proven to provide valuable proxies for climate reconstructions. Density measurements were successfully used in the field of dendroclimatology in the past, with recent efforts to obtain sub-annual predictors from density profiles. Particular attention is laid on anomalies in the density profile named intra-annual density fluctuations (IADFs). Density fluctuations in earlywood with higher than ordinary density are assumed to be triggered by drought events in spring or early summer. How they are formed, linked to chemical and anatomical characteristics and their functionality is not well understood, although necessary to interpret growth-climate relationships of this trait. An explorative assessment of radial profiles from silver fir, showing an IADF in earlywood of 2005, included cell wall and lumen area, cellulose to lignin ratio, microfibril angle, tracheid length as well as size and shape of pits, beside density. The resulting synoptic view of these traits depicted deviations at the IADF position, indicating that multiple phases of wood formation are affected by a triggering event. These anatomical and chemical adaptions result in a hydraulically safer tissue with improved mechanical strength. The presented approach provides first insights on multiple involved wood traits and leads towards a more comprehensive understanding of IADF formation.