title: Timing of False Ring Formation in Pinus halepensis and Arbutus unedo in Southern Italy: Outlook from an Analysis of Xylogenesis and Tree-Ring Chronologies.
abstract: Mediterranean tree rings are characterized by intra-annual density fluctuations (IADFs) due to partly climate-driven cambial activity. IADFs are used as structural signals to gain information on relations between environmental conditions and eco-physiological processes during xylogenesis, with intra-annual resolution. To reach an unbiased synchronization of the IADF position within tree rings and seasonal fluctuations in environmental conditions, it is necessary to know the timing of cambial activity and wood formation, which are species- and site-specific processes. We applied the microcoring technique to analyze xylogenesis in Pinus halepensis and Arbutus unedo. To the best of our knowledge, this is the first attempt to study xylogenesis in a hardwood species forming frequent IADFs. Both species co-occur at a site in southern Italy characterized by a Mediterranean climate. To facilitate tree-ring dating and identification of IADFs, we performed traditional dendroecological analysis. We analyzed xylogenesis during summer, which is considered a constraint for xylogenesis and a trigger for IADF formation. We followed the different phases of cell development in the current wood increment with the aim of evaluating whether and which type of IADFs were formed. We additionally analyzed the same phases again in September and in winter to verify the possible formation of IADFs in fall and whether cell production and differentiation was completed by the end of the calendar year. Both species formed the same type of IADFs (earlywood-like cells within latewood), due to temporary growth restoration triggered by rain events during the period of summer drought. At the end of the calendar year, no cells in the phases of enlargement and secondary cell wall deposition occurred. A. unedo was more sensitive than P. halepensis because IADFs were formed earlier in the season and were more frequent in the tree-ring series. The dendro-anatomical approach, combining analysis of tree-ring series and of xylogenesis, helped to detect the period of IADF formation in the two species. Results are discussed in functional terms, highlighting the environmental conditions triggering IADFs, and also in methodological terms, evaluating the applicability of xylogenesis analysis in Mediterranean woods, especially when the formation of IADFs is not uniform around the stem.
authors.affiliation: Department of Agricultural Sciences, University of Naples Federico II, Naples Italy.
authors.forename: Veronica
authors.initials: V
authors.lastname: De Micco
authors.affiliation: Department of Agricultural Sciences, University of Naples Federico II, Naples Italy.
authors.forename: Angela
authors.initials: A
authors.lastname: Balzano
authors.affiliation: Biotechnical Faculty, Department of Wood Science and Technology, University of Ljubljana, Ljubljana Slovenia.
authors.forename: Katarina
authors.initials: K
authors.lastname: Čufar
authors.affiliation: Department of Agricultural Sciences, University of Naples Federico II, Naples Italy.
authors.forename: Giovanna
authors.initials: G
authors.lastname: Aronne
authors.affiliation: Slovenian Forestry Institute, Ljubljana Slovenia.
authors.forename: Jožica
authors.initials: J
authors.lastname: Gričar
authors.affiliation: Biotechnical Faculty, Department of Wood Science and Technology, University of Ljubljana, Ljubljana Slovenia.
authors.forename: Maks
authors.initials: M
authors.lastname: Merela
authors.affiliation: Department of Environmental, Biological and Pharmaceutical Sciences and Technologies, Second University of Naples, CasertaItaly; Laboratoire Paléoenvironnements et Chronoécologie, École Pratique des Hautes Études, Université de Montpellier, MontpellierFrance.
authors.forename: Giovanna
authors.initials: G
authors.lastname: Battipaglia
keywords: cambial activity; cambial phenology; intra-annual density fluctuations; mediterranean climate; tree rings