The carbon-14 bomb peak as a turning point in dendrochronology in tropics: A literature review and case study with Araucaria angustifolia

Abstract

Establishing reliable tree-ring chronologies in the tropics remains a challenge, however, it can be mitigated by combining direct and indirect methods. This study investigates the synergy between classical dendrochronology and radiocarbon (¹⁴C) dating. For this purpose, we developed a preliminary chronology for Araucaria angustifolia in southern Brazil and a compilation of ¹⁴C applications in Brazilian dendrochronology. We tested the synchronicity of tree growth using classical dendrochronological methods on samples from three trees. Radiocarbon analysis of selected tree rings, specifically those formed during the ¹⁴C bomb peak, confirmed the annual nature of growth rings and validated the accuracy of our classical dating. While initial dating discrepancies were observed, these were resolved by considering the variability in the onset of cambial activity for this species. The mean series intercorrelation increased after analyzing the synchronicity in tree growth variability (number of samples n = 3, period 1930–2018) before (r = 0.366) and after (r = 0.423) the adjustments. Our findings demonstrate the effectiveness of combining classical dendrochronology and ¹⁴C dating to establish robust chronologies, particularly for tropical and subtropical species such as A. angustifolia that present dating challenges. This preliminary chronology provides a robust reference for developing a more comprehensive and well-replicated A. angustifolia chronology for subtropical Brazil. Additionally, the literature review showed that radiocarbon dating studies in Brazil, while still relatively scarce (21 studies) and with an uneven geographic distribution, have significantly advanced over the past 5 years. Our case study highlights the growing importance of ¹⁴C analysis in tree-ring research in Brazil and emphasizes the need for further studies to refine ¹⁴C calibration curves for the Southern Hemisphere.