The potential of Tectona grandis at Mtibwa to act as a carbon sink

The fieldwork took place at Mtibwa Teak Project, Morogoro, Tanzania. Two compartments were dealt with six trees from each compartment were selected, representing the diameter range between 17 – 43 cm Dbh. The trees were felled and divided into stem and branches. The leaves were fathered and the root system excavated. Total fresh weights were measured. Sub-samples of the components were weighed fresh in the field and brought to laboratory for moisture content determination. Total dry weights of the components were calculated, using the dry to fresh weight ratio. It was found that the dry weight increased with increasing Dbh for all components. This was not true when height was included. Stemwood density was found to be 0.520 and 0.540g/cm3 on average for compartments No. 1 and 2 respectively. The share of biomass in the different tree components did not vary significantly with a change in tree size. The stem to total biomass ratio was rather constant within the diameter range of the sample trees. Thus, stem biomass was used as a basis for calculating total biomass. A simple regression equation or total biomass: TOB = 963 + 53.9 DBH was performed for material. The equation explained 87% of the variation in total biomass, and a test of significance showed that both coefficients had proved useful in determining the association. Priority was given to calculate the net fixation of carbon dioxide per hectare during a rotation period. Stem volume increment data were converted to biomass using the basic density of teak of 0.589 g/cm3 cited in the literature and 37% were added as the contribution of branches and roots to the total and about 50% of the dry weight was assumed to be carbon. Conversion from carbon to carbon dioxide was done by multiplying the molecular weights in the relation CO2/C. The alternatives of fixation for a rotation period of 60 yeas with regards to growth and yield pattern were calculated. One corresponded to best site quality teak plantation yield and stand table for India. The other was synthesized from present thinning schedule and previous growth performance studies, indicating vigorous growth in early stages for Tanzanian plantations. Different average time in use and decay rates for tree components and products were incorporated. No decay while in use was assumed, and a linear decomposition pattern was adopted. The alternative following Indian stand and yield table sequestered a total of 595 ton CO2/ha after 60 years, which give an average annual fixation of 10 ton CO2/ha. The alternative adopting modified extraction schedule and growth for Tanzania sequestered a total of 844 ton CO2/ha, leading to an annual average fixation of 14 ton CO2/ha. Different growth development, thinning schedule and assortment percentages contributed to the variation in the results.