A new chronology of Cedrela fissilis (Meliaceae) for Southern Brazil: a combination of classical dendrochronology, climate, and radiocarbon dating

Abstract

In Brazil, most of the climate database began to be built in 1960. However, to understand thephenomena related to climate change, it is necessary to go back much further in time. One wayto access past climate data is using proxies, such as dendrochronology, centered on dating thegrowth rings of trees. Therefore, it is necessary to use plants that form yearly rings that coincidewith recurrent variations in the environment, and these organisms have a long lifespan as well.Cedrela fissilis is a long-lived tree that exceed 350 years, the growth rings are formed annually,and it is widely distributed in the South American Hemisphere. Starting from the premise thatin the tropical regions of Brazil, the genus Cedrela forms annual growth rings, the present workaims to develop a chronology of Cedrela fissilis: i. to investigate by cross-dating whether trees(70-110 years of age) form synchronous rings in time that can be cross-dated; ii. to validate thedating of the chronology by the 14C bomb pulse method; iii. to test the influence of temperatureand precipitation on the radial growth of the species. If the growth rings are well correlated witheach other and with local climate variables, it will be possible to use the C. fissilis chronologiesto reconstruct the past climate of the region. The study area is in the Brazilian Southern Plateau(27° 9.908´S; 51° 34.639´W). The chronology was built using 24 trees. High resolution imageswere used to date the growth rings. Visual dating was checked using Cofecha, and thechronology built in Arstan. The years 1957, 1962, 1963, 1966, 1969 and 1974 were selected tobe evaluated by the 14C bomb pulse method. To test the regional climate, the standarddeviations of the data obtained from two meteorological stations were calculated. Thechronology covers the period 1907-2018 (111 years). Statistics indicate that the chronology ishighly reliable and of good quality (r = 0.49; rBar = 0.30; EPS = 0.86; MSI = 0.40). The 14C bombpulse showed that the trees were accurately dated by the classical cross-dating approach. Thecomparison between the interannual variation of growth and the deviations of precipitationfrom November to January (wet period), the growth rings are positively correlated (r =0.36,n=49; p<0.05). Likewise, May-July temperature deviations and interannual variations in ringwidth are positively correlated (r=0.39, n=49; p<0.05). Summarizing, the growth is favored byperiods with abundant rainfall and low winter temperatures act negatively. This responsesuggests that the species is very sensitive to climatic variations, mainly to interannual changesin soil moisture during the growth period. Radiocarbon analysis showed that C. fissilis formsannual growth rings, even in places where the rainfall regime is relatively equally distributedthroughout the year. The consistent match between 14C signatures in tree rings with thoseexpected for the atmosphere during the nuclear era (after 1950) confirmed that well-datedsubtropical tree-ring records can be used for paleoclimatic reconstructions of these regions, inaddition to many other applications in ecological studies.