The importance of hydraulic conductivity and wood density to growth performance in eight tree species from a tropical semi-dry climate

Understanding how tropical trees coordinate fast growth with water consumption and carbon investment is of high relevance because climate warming may expose tropical forests to increasing stress. Thus, foresters require more information of native tree species envisaged for reforestation. This study examines the relationship between productivity and possibly growth-determining functional traits of xylem anatomy, hydraulic conductivity, foliar morphology and nutrient status in eight tree species in semi-dry Costa Rica; we further assessed the indicative value of wood density for growth rate and hydraulic efficiency. We tested the hypotheses that (i) wood density is related to both growth rate and hydraulic efficiency contrary to findings from moist tropical forests, and (ii) productivity is closely related to branch xylem properties as well as empirically determined hydraulic conductivity in these drought-adapted species. Growth rate was positively related to tree size, foliar nitrogen content, vessel diameter, specific conductivity and leaf water potential, and negatively to vessel density, wood density and δ13C, indicating that fast-growing tree species with light wood possessed a more efficient hydraulic system but closed their stomata relatively early to prevent xylem dysfunction. We conclude, that in tropical semi-dry climates, productivity is closely associated not only with foliar nitrogen but also with wood anatomical and hydraulic properties. Wood density proved to be a reliable indicator for growth-related, wood anatomical and hydraulic traits in these drought-adapted species.