Adaptation et variabilité génétique de la croissance de #Liquidambar styraciflua# L. de l'essai de provenances à Mandraka, Madagascar

Liquidambar styraciflua , or the American sweet-gum tree, is a deciduous species origi- nating in the south-eastern United States and Central America. Its behaviour in plantations is outstanding and its timber is used for mul- tiple purposes. In 1986, under an interna- tional provenance trial, the Commonwealth Forestry Institute (CFI) in Oxford distributed Liquidambar styraciflua seeds of thirteen dif- ferent provenances, mainly harvested in the natural range of distribution of the species extending from the eastern United States to Mexico and Central America. In Madagascar, they were planted by the forestry and fish- eries research department (DRFP-FOFIFA) at Mandraka. Data on annual growth were col- lected for 25 years, but the results, unlike those for Brazil and Mexico, have not yet been published. The aim of our study was to assess adaptation of the species in Man- draka and to investigate intra-species growth variability. Up to 25 years of age, the trees grew steadily to reach, on average, a height of 26 m, a diameter of 38 cm and a basal area of 0.12 m² per tree. These average val- ues differ significantly according to prove- nance. At 25 years of age, heritability in the broad sense is 0.76, 0.60 and 0.63 for height, diameter and basal area respectively, indicating genetic control over growth. Under similar ecological conditions and at equiva- lent age, the growth of L. styraciflua is equiv- alent to that of species of the genus Eucalyp- tus and better than in Pinus . In comparison with the international CFI trials, the prove- nance trial for L. styraciflua at the Mandraka site shows better adaptation and a high growth rate for the species.