Annual Chronology and Climate Signals in Swietenia macrophylla and Cedrela odorata (Meliaceae) in the Maya Lowlands

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 gap can be attributed 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 locally absent rings can make the process of visually crossdating lowland tropical species extremely challenging. Here, we combine traditional dendrochronological techniques with high-precision radiocarbon bomb-pulse dating and wood anatomical analysis 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 indicated an initial misdating due to the anatomical challenges encountered during visual and graphical crossdating. We demonstrate how the iterative use of dendrochronological, wood anatomical, and radiocarbon methods allowed us to correct, validate and assign exact calendar dates to our tree-ring series. 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 timing of the Midsummer Drought 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, including climate reconstructions, as well as the potential to develop annually resolved (Formula presented.) records in the lowlands of Central America.