Stem Quality and Wood Basic Density of Eucalyptus Species Grown at Wino Forest Plantation, Ruvuma Region, Tanzania

Understanding variation in stem form and wood basic density (WBD) is essential for selecting Eucalyptus species suited to saw timber, pole production, and bioenergy in Tanzania. This study quantified differences in stem straightness, forking, damage, and WBD among 40 Eucalyptus entries (38 species/provenances and two GC hybrid clones) in an eight-year replicated trial at Wino Forest Plantation, southern Tanzania. Stem quality traits were visually scored and combined into a Composite Stem Quality Score (CSQS), while WBD was determined from breast-height increment cores using the gravimetric method. Statistical analyses revealed significant genetic variation. Stem straightness and forking differed highly significantly (χ²(78) = 950.0 and χ²(78) = 156.6, respectively; p < 0.001), whereas damage showed no significant variation (p = 0.971), indicating uniform environmental effects. WBD also varied strongly (F(39, 120) = 7.82, p < 0.001), ranging from 388 kg m⁻³ (E. argophloia) to 723 kg m⁻³ (E. biturbinata). A weak negative correlation (r = –0.249, p = 0.121) between CSQS and WBD suggested a mild trade-off between stem form and wood density. The highest straightness (>90%) was observed in E. cloeziana, GC15_GRL, and selected E. grandis provenances, while E. alba and E. globulus had the lowest (