Evidence for Annual Tree Ring Formation in Swietenia macrophylla King and Cedrela odorata L. (Meliaceae) in the Maya Lowlands

Abstract

Despite efforts over recent decades, a gap persists in the global network of tree-ring chronologies in the tropical Americas and especially for low-elevation sites. This is primarily due to the inherent challenges in identifying tropical species well-suited for dendrochronology that form reliably annual rings. Even when seasonal growth rhythms do exist, properly distinguishing true annual boundaries from false rings and identifying any missing rings can make the process of visually crossdating tropical species laborious and challenging. Here, we combine traditional dendrochronological techniques with high-precision radiocarbon bomb-pulse dating to confirm annual ring formation in Cedrela odorata L and Swietenia macrophylla King (Meliaceae) in the northern Maya lowlands of Guatemala. Our findings indicate annual ring formation in both species, but the radiocarbon measurements also identified misdating due to the anatomical challenges identified during visual and graphical crossdating. Once the exact chronology was established, we found that tree-ring width in both species is influenced by precipitation during June, July and August, which coincides with the Midsummer Drought and the second peak of rainfall in the Central American precipitation regime. Successfully demonstrating annual tree growth periodicity in Cedrela odorata and Swietenia macrophylla establishes the groundwork for future tree-ring research with these species, as well as the potential to develop annually resolved radiocarbon records in the lowlands of Central America.