Wood Basic Density, Stem Quality, and Disease Resistance of Corymbia and Eucalyptus Species at North Ruvu Forest Plantation, Kibaha District, Tanzania

Forest plantations in Tanzania play a critical role in supporting sustainable wood supply hence reducing pressure on natural forests. However, expansion of forest plantations in the coastal lowland areas remains constrained by the limited availability of appropriate tree species that combine varieties of traits such as acceptable wood quality, stem form, and resistance to biotic stresses in order to cope with the challenging site conditions. This study evaluated wood basic density (WBD), stem quality, and disease resistance of eight-year-old Corymbia and Eucalyptus pure species/provenances grown at North Ruvu Forest Plantation, Kibaha District, Tanzania. The trials were established using a randomized complete block design (RCBD), with five replications for Corymbia and six for Eucalyptus. WBD was determined from increment core samples, while stem quality and disease resistance were assessed in the field using standardized visual scoring systems. The results (presented as mean ± standard error (SE)) shows that (Corymbia species/provenances differed significantly in WBD, ranging from 385 ± 18 kg m-3 (C. henryi, CSIRO) to 475 ± 27 kg m-3 (C. citriodora, TTSA). In contrast, Eucalyptus species showed lower and more uniform WBD values (mean = 394 ± 0.9 kg m-3), with no significant differences detected among entries. C. variegata (CSIRO) and C. citriodora (TTSA) showed the highest stem quality, with 100% and 92% high-quality stems, respectively. Disease resistance was strongest in C. citriodora (TTSA and ZFC) and E. camaldulensis (TTSA), where no visible disease symptoms were observed. Overall performance ranking identified C. citriodora (TTSA), C. variegata (CSIRO), and E. camaldulensis (TTSA) as the most promising species/provenances for coastal lowland conditions. These findings demonstrate the strong potential of selected Corymbia species as viable alternatives or complements to Eucalyptus in Tanzanian plantation forestry and provide empirical guidance for site–species matching and diversification strategies in similar environments.