Soil Properties and Site Index in an Age Sequence of Gmelina arborea in Jalingo Taraba State, Nigeria

Soil potential productivity and the site index in an age Gmelina arborea plantation in Jalingo forest plantation were studied. The plantations which were of different age variations, were mapped out into eight compartments with a measurement of 100 m x 100 m. For each of the compartment 16 plots were unmarked, 25 m x 25 m (0.0625 ha) out of which three plots was randomly selected as sampled plots. In each of the sampled plots, site factors were measured. In identifying mean trees, all the stems in each plot were distributed into basal area classes range as 15- 50 cm, 55-85 cm and 86-121 cm tagged A, B and C respectively. The soil samples were assessed in the laboratory for the physical and chemical properties. The results showed that soils in the Gmelina plantation are generally slightly acidic; and acidity increases with increase in the soil depth. For the height of Gmelina arborea plantation, the results showed that not all variables contributed fully to the growth and development of the trees height. Semi-log regression model seems to yield better of the equations.