Résumé
Despite the continuous nature of growth of eucalyptus hybrids in Congo, taper functions fitted to stem profiles of one clone throughout stand development, combined with annual tree measurements, made it possible to locate accurately the position of annual rings in stems. Annual rings were identified on discs of wood sampled every 4 m in four trees cut from 1-, 2-, 3-, 4-, 5-, 6- and 7-year-old stands. Chemical analysis, performed individually for each ring per level and per tree sampled, made it possible to quantify the changes in nutrient content of the rings during stand development. Nutrient translocation in stemwood was thus calculated in a stepwise manner between trees of two successive ages. The cumulated nutrient translocations in stemwood from the 1-year-old stage to the 6-year-old stage amounted to 18·5 kg ha−1N, 4·2 kg ha−1P, 38·8 kg ha−1K, 1·5 kg ha−1Ca and 3·2 kg ha−1Mg. They represented 11, 18, 121, 6, and 15% of the amounts of N, P, K, Ca and Mg accumulated in stemwood, respectively, at the 7-year-old stage (logging age). Negative translocations of N, P, Ca and Mg in stemwood between 6 and 7 years might indicate an improvement in the nutritive status of the stand at the end of the rotation. Much translocation of K in stemwood suggests that this process might be involved in the high use efficiency of this element.