Thinning Compliance and its Effects on Growth, Yield and Stem Quality of Tectona grandis at Mtibwa Forest Plantation, Morogoro, Tanzania

Abstract

Observing thinning schedule in commercial tree plantation is crucial if the final crop of desirable quality is required. However, there is limited information on thinning compliance to thinning schedule of Tectona grandis (Teak) in Tanzania. This study was undertaken to assess thinning compliance and its effects on the growth and yield of Teak at Mtibwa Forest Plantation, Morogoro, Tanzania. Ninety-two (92) circular plots of 9.78m radius were laid in 23 purposively selected compartments. Thinning history, heights of 3 fattest trees, breast height diameter (Dbh), and stem quality of trees in a plot were recorded. Results show that 57% of the thinned area is overstocked compared to the thinning schedule whereby the second and third thinnings had significantly higher (P < 0.05) stems per hectare (SPH). Inadequate thinning affects Dbh growth by 6-10% but dominant height (Hdom) is unaffected. SPH, basal area (BA), and volume (Vol) are higher by 15-69%, 4-118%, and 3-149% respectively. Results indicate that 73-80% of trees in compartments have stem quality 2. Generally, thinning is delayed, and lighter than recommended in the thinning schedule with negative effects to stand growth and yield. Compliance with the thinning schedule is recommended to attain the projected growth at rotation age.