Radiocarbon and wood anatomy as key novel tools to generate an annual tree-ring chronology from Prosopis alba in the tropical Bolivian Andes

ARTURO PACHECO-SOLANA; LAIA ANDREU-HAYLES; ERNESTO TEJEDOR VARGAS; M. EUGENIA FERRERO; MILAGROS RODRÍGUEZ-CATÓN; CARLA MALDONADO; GUACIARA M. SANTOS

New Orleans, LA & Online

Conferencia; American Geophysical Union -AGU- Fall Meeting; 2021

American Geophysical Union

Tree-ring boundaries in tropical species are often less clear and less reliable than its counterparts from temperate zones (Worbes 2002). While in extratropical areas well-defined changes in temperatures drive the onset and offset of the growing season, in tropical environments trees may experience cambial dormancy or rapid growth periods mostly related with the hydrological cycle such as dry seasons or heavy rain periods. In addition, intra-seasonal fluctuations on climate may cause the formation of false rings, wedging rings or non-clear anatomical ring features (Dünisch et al. 2003; Wils et al. 2009). Although this myriad of factors contributed to make tropical tree-ring analyses very challenging, the number of studies and tree species described with dendrochronological potential is increasing. Here, we present an annual tree-ring chronology of Prosopis alba (21°70?27??S ? 64°59?90??W, 1690 masl), a tree species growing on the dry highlands of southern Bolivia where a distinctive rain seasons occurs. While annual periodicity have been reported for other Prosopis species like P. ferrox (Morales et al. 2001) and P.flexuosa (Giantomasi et al. 2009), the dendrochronological potential of P. alba remain unrevealed. We collected several discs of P. alba, visually crossdated and measured a minimum of 4 radii per tree finding correlation coefficients values among different trees radii ranging from 0.3 to 0.5, showing some degree of growth synchronicity among trees. To validate the dendrochronological calendar years, we performed radiocarbon analysis obtaining offsets of 5 and 12 years on two analysed samples. We anchored our tree-ring samples to the 14C calendar dates and perform stem microsections to have a finer detail of the specific anatomical characteristics. Wood microsections revealed very narrow terminal parenchyma defining tree-ring boundaries undetectable using classical approaches. These challenging tree-ring boundaries were mostly present within the sapwood area of all the samples analysed. Our work pointed out radiocarbon and wood anatomical analyses as key tools to generate tree-ring chronologies with annual resolution in some tropical tree species and the potential of P. alba for dendrochronological studies.