Early evaluation of Racosperma auriculiforme and R. mangium provenance trials on four sites in Zaire.

Abstract

Provenance variation was examined in two Racosperma species (Racosperma auriculiforme [Acacia auriculiformis] and R. mangium [A. mangium]) on four test sites in Zaire. The sites were: Mampu (Bateke plateau), a low fertility savanna with acidic (pH 4.4) sandy soil; Kipopo (Lubumbashi), an abandoned shifting cultivation pasture in miombo with clay loam acidic (pH 4.3) soil; Kinkudu (Luki), a savanna with loamy sand, pH 5.1 and low P and potential boron deficiency; and Baki (Muanda), a low fertility savanna with marine sand and acidic (pH 5.2) soil. Seeds for the two species were obtained from Northern Territory and Queensland, Australia, Papua New Guinea, Indonesia, Congo and Zaire. Growth and morphological characters (height, diameter, number of stems, branch angle, stem straightness, volume and flowering), survival and wood specific gravity were measured at ages 3, 9, 15 and 21 months. Site effects were significant and significant provenance differences existed in all traits except branch angle. The rank of provenances changed across sites, indicating significant genotype×environment interactions. Correlations of field growth traits (diameter, height and volume) at different ages were positive but negatively correlated with nursery results. Clinal variation was observed, especially for survival rate. The provenances with the greatest volume production were from Papua New Guinea. These multipurpose tree species are suitable for reforestation programmes in Zaire, such as short rotation (7-yr) fuelwood plantations and for use in agroforestry systems. Additional genetic gains in growth and wood density could be obtained through selection and breeding of superior individuals from these provenances.