Growth of Amburana cearensis (roble) in the Chiquitano forests of Santa Cruz, Bolivia

Abstract

Dendrochronology serves as a highly effective tool for assessing tree growth variation and reconstructing the climatic history of a specific region or biome. Utilizing established traditional techniques in dendrochronology, the growth variation of 15 Amburana cearensis trees was evaluated in the Chiquitano dry forest (CIMAL) of Santa Cruz, Bolivia. The primary objective was to ascertain the relationship between growth and regional climatic variations. The analyzed trees exhibit annual rings that are visible and defined by continuous to semi-continuous marginal parenchyma, located at the end of each growth period. In CIMAL, this species comprises trees that exceed 120 years in age and grow at an average rate of 0.50 cm annually. The autocorrelation among trees (r = 0.61), the mean correlation between series (R-bar = 0.40), and a mean population signal (EPS = 0.93) indicate that the chronology is composed of a robust replication of specimens across all segments. The growth of A. cearensis trees is enhanced during periods of abundant rainfall and relatively lower temperatures compared to the annual mean values. The interannual growth variation and the instrumental records of temperature (r = -0.34) and precipitation (r = 0.61) are significant in both cases. Growth is positively correlated with precipitation from December to March, while the temperature during the same period shows a significant inverse correlation. This response pattern suggests that the growth of this species is highly sensitive to climatic variations, particularly to interannual changes in water supply. The radial growth of A. cearensis in the Chiquitano dry forests is primarily influenced by water availability, as indicated by the positive relationships with seasonal precipitation and negative correlations with the annual mean temperature. This response serves as evidence of the dendrochronological potential. This response serves as a test of the dendrochronological potential that this species possesses for reconstructing past precipitation variations in the extensive tropical forest formations of the Cerrado and Chaco regions in South America.