Growth Rate and Climatic Response ofMachaerium scleroxylonIn a Dry Tropical Forest In Southeastern Santa Cruz, Bolivia

Abstract

Machaerium scleroxylon (morado) is an important timber species from the lowland tropical dry forests in Bolivia. We followed a dendrochronological approach to (i) evaluate the responses of radial growth to climatic variables and atmospheric circulation patterns, and (ii) quantify the growth rate in order to estimate the Minimum Logging Diameter (MLD), age, and optimal cutting rotation. We measured tree-ring width in wood discs taken from ten randomly selected mature individuals. We used previous histological analyses to distinguish and visually crossdate tree rings. Despite the existence of false rings, lenses and wedging rings, the species showed defined annual ring boundaries, thus enabling a tree-ring chronology analysis. Correlations between residual ring-width indices and monthly climatic variables (temperature and rainfall) and atmospheric circulation patterns (El Niño-Southern Oscillation) index were calculated. Growth showed a significant positive correlation with monthly rainfall and a negative correlation with mean temperature during the late rainy season (i.e. from December up to March). A positive correlation found between the ring width and ENSO indices indicates that the growth of M. scleroxylon was significantly affected by atmospheric circulation patterns. Growth rate is slow in morado, suggesting a MLD of 50 cm and an optimal cutting cycle longer than 40 years depending on each site.