Investigating the wood production and adaptability potential of Corymbia hybrid progeny in northern coastal Zululand, South Africa

Abstract

During August 2013, two ‘new’ eucalypt taxa × site interaction trials were established in northern coastal Zululand. The main purpose of these trials was to investigate the commercial forestry potential of a range of Corymbia inter-specific hybrids for the region. Two sites contrasting in mean annual precipitation (850 mm and 1 155 mm respectively) and productivity potential, namely Mfezi (Mtubatuba) and Flatcrown (Kwambonambi), were selected for these trials. The 28 Corymbia hybrid seedlots comprised controlled crosses between C. torelliana and C. citriodora subsp citriodora, C. citriodora subsp variegata and C. henryi. Trees were assessed annually for the presence of pests and diseases and at mid-rotation (48 months) comprehensively measured for growth. By mid-rotation, none of the Corymbia hybrid
families showed susceptibility to the suite of insect pests plaguing many of the commercial Eucalyptus hybrid clones in the region. Furthermore, no noteworthy disease infection symptoms were observed in any of the Corymbia or Eucalyptus species and hybrids in the trials. At the drier site of the two (Mfezi), at 24 months following 2 successive dry (<700 mm rainfall) years, trees of some of the Corymbia hybrid families manifested drought stress symptoms in the form of mild to moderate kino exudations from stems and branches. However, by mid-rotation, most of the Corymbia hybrid families in the trial showed excellent tree health, survival and stem volume relative to that of the commercial hybrid controls. At both sites, the seven top-ranking treatments for volume were Corymbia hybrid families. Based on the overall excellent growth performances of several of the Corymbia hybrid families in the two trials, more intensive investigations, for example in the areas of wood properties, vegetative propagation and clonal performance testing, would appear well-warranted.