Does Cedrela always form annual rings? Testing ring periodicity across South America using radiocarbon dating

Abstract

Key Message Radiocarbon dating shows that Cedrela trees from Bolivia, Ecuador and Venezuela form one ring per year but Cedrela trees from Suriname form two rings per year. Abstract Tropical tree rings have the potential to yield valuable ecological and climate information, on the condition that rings are annual and accurately dated. It is important to understand the factors controlling ring formation, since regional variation in these factors could cause trees in different regions to form tree rings at different times. Here, we use 'bomb-peak' radiocarbon ( 14 C) dating to test the periodicity of ring formation in Cedrela trees from four sites across tropical South America. We show that trees from Bolivia, Ecuador and Venezuela have reliably annual tree rings, while trees from Suriname regularly form two rings per year. This proves that while tree rings of a particular species may be demonstrably annual at one site, this does not imply that rings are formed annually in other locations. We explore possible drivers of variation in ring periodicity and find that Cedrela growth rhythms are most likely caused by precipitation seasonality, with a possible degree of genetic control. Therefore, tree-ring studies undertaken at new locations in the tropics require independent validation of the annual nature of tree rings, irrespective of how the studied species behaves in other locations.

Climatic Response of Cedrela fissilis Radial Growth in the Ombrophilous Mixed Forest, Paraná, Brazil

“…In regions where drought and rain periods occur regularly, the influence of precipitation can be seen more clearly. In the Amazon basin, Baker et al (2017) explored possible variation factors in the periodicity tree-rings from Cedrela species and affirm that growth rates are probably influenced by the seasonality of the precipitations. In the same way, a research developed in a tropical dry forest in eastern Bolivia, showed that C. fissilis was sensitive to precipitation in almost all analyzed time scales, with leaf flushing and radial-increment rate related to a synchronous response to water availability (Mendivelso et al, 2016).…”

“…However, the relationship between these climatic elements and growth is not a direct one, since it is not possible to be sure if the resources will be available (Ribeiro et al, 2011). It is important to understand the factors controlling ring formation at smaller scales, since the variation of these factors between regions may cause trees in different regions to form rings at different times (Baker et al, 2017).…”

When the carbon being dated is not what you think it is: Insights from phytolith carbon research

“…Therefore, when dealing with plant parts and remains it is also recommended to chemically isolate the fraction of carbon for 14 C dating. For 14 C tree ring studies, for instance, "cellulose" -also termed alpha-cellulose (Leavitt and Bannister, 2009), or hollocelulose extract (Southon and Magana, 2010;Santos et al, 2015;Baker et al, 2017) -is the preferable structural component of plants to be used for 14 C dating.…”

“…Such large variations are extremely unlikely in regions with very low anthropogenic CO 2 emissions (Hansen and Sato, 2016). Moreover, large discrepancies should have been apparent for other Neotropical biomass archives across the region (Dezzeo et al, 2003;Santos et al, 2016;Baker et al, 2017). Regardless, validation experiments using poorly or improperly characterized materials are pointless.…”

High resolution <sup>14</sup>C bomb-peak dating and climate response analyses of subseasonal stable isotope signals in wood of the African baobab – A case study from Oman

“…Reliable age estimates of tropical and subtropical trees can be obtained from radiocarbon dating (Swart, 1963;Worbes, 1989). Using the bomb peak caused by extensive nuclear testing in the 1950s and 60s, radiocarbon dating was proven a reliable tool in plant sciences that enables dendrochronological studies on trees with indistinct growth boundaries (Fichtler et al, 2003;Hua et al, 2003;Robertson et al, 2006;Andreu-Hayles et al, 2015;Ohashi et al, 2016;Baker et al, 2017;Linares et al, 2017). The vast majority of bomb tests have been carried out in the Northern Hemisphere.…”