Influence of site-specific soil and topographic factors on teak growth in the Kilombero Valley, Tanzania

Teak (Tectona grandis) is a highly valued tropical timber species widely cultivated across the tropics. In Tanzania, it is an important industrial timber, with the Kilombero Valley Teak Company (KVTC) being a major producer. Despite standardized silvicultural practices, substantial growth variation occurs within KVTC plantations, yet quantification of intra-block soil and topographic heterogeneity is limited. This study assessed the contribution of environmental factors to teak growth by integrating diameter at breast height (DBH), total height, and dominant height measurements from 48 permanent sample plots (PSPs) with fine-scale soil (pH, organic carbon, bulk density, texture) and topographic (slope, elevation) attributes across four plantation blocks of varying site qualities and stand ages. ANOVA revealed significant effects of site class (DBH: F = 167.8, p < 0.0001; height: F = 182.0, p < 0.0001; dominant height: F = 40.1, p < 0.001), age (p < 0.0001), and a strong site × age interaction (p < 0.0001). Regression analysis indicated that a 1 unit increase in soil organic carbon and silt content corresponded to dominant height increases of 15.5% (β = 0.155, p = 0.011) and 0.86% (β = 0.0086, p = 0.003), respectively (adjusted R2 = 0.255). These findings highlight dynamic site growth interactions mostly driven by intra-block edaphic variability. Although models explained moderate variance at the plantation scale, the results demonstrate how localized gradients underlie microsite productivity variation. The findings support precision silviculture through site-specific management strategies such as soil amendments and resource allocation to optimize teak productivity in Tanzania and similar regions.