INDEX AGE FOR ESTIMATING SITE INDEX OF Gmelina arborea (ROXB.) STANDS IN OLUWA FOREST RESERVE, SOUTH WESTERN NIGERIA
Abstract
Index age for estimating site index of Gmelina arborea (Roxb) stands in Oluwa forest reserve in six year old plantation and ten year old plantation was investigated in this study. A hectare was randomly selected in each of the plantations. Temporary sample plots of 20m x 20m were laid while complete enumeration were carried out in each sampled plot and tree growth variables such as diameter at breast height (Dbh), diameter at the top, diameter at the middle and diameter at the base as well as total height of all trees were measured. Site index equation was constructed using simple linear regression model. The derived site index equation for Gmelina arborea plantation in the study area was: SI = exp [Ln(Hd) – 2.85 ( (0.05) – A-1)]. Based on the site index, a harvesting age of 20 years was found appropriate for the site. Total volume was found to be 2396.94m3 and 10257.07m3 for 6 years and 10 years old respectively. The
maximum Dbh encountered was 0.55m and that of height was 25.5m. For diameter distribution, highest proportion (54%) of the tree per hectare of 10 years old stand of G. arborea belong to diameter class of 30-39cm while the least proportion (1%) belong to Dbh class of 50-59cm. Also for 6 years old stand the highest proportion (51%) and the lowest (2%) belong to Dbh class of 10-19cm and 30-39cm respectively. Initial timber harvesting and further re-establishment of Gmelina arborea plantations in Oluwa forest reserve should be concentrated upon.
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