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The Fate of a Tropical Rainforest in Nigeria: Abeku Sector of Omo Forest Reserve

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Pages :
116 - 130

Ojo O. L.
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Sixteen permanent sample plots of one hectare each, established in 1985 at Abeku sector of Omo
Forest Reserve, South west Nigeria by the European Economic Community/ Nigeria Federal
Government (High Forest Monitoring Plots Project) (EEC/HFMPP) were used for this study. The plots
were re-enumerated in 1987. Further assessment took place in 1997 and 2000 respectively for the
purpose of assessing the floristic characteristics of the plots. The present study aims at assessing the
floristic composition during the sampling years. Out of the original 16 plots only eleven and nine plots
were available for assessment in 1997 and 2000 respectively. The remaining plots had been converted
to plantations of arable and cash crops. The numbers of tree species encountered were 98, 109, 95 and
71 for 1985, 1987, 1997 and 2000 enumerations respectively. Also 28,31, 29 and 23 families were
encountered in 1985, 1987, 1997 and 2000 respectively. In terms of density, basal area and spread, the
ten most abundant species are Diospyros iturensis (Plant nomenclature follows Hutchinson and
Dalziel (1954-72); Keay (1989) and Lowe and Soladoye (1990)), (DIAL),Tabernaemontana
pachysiphon (TAPA), Octolobus angustatus (OLAN), Strombosia pustulata (SBPU), Diospyros dendo
(DIDE), Diospyros suaveolens (DISU), Drypetes gossweileri (DRGO), Rothmania hispida (ROHI),
Hunteria unbellata (HUUM) and Anthonotha aubryanum (ASAU) and the six most prominent families
are Ebenaceae, Apocynaceae, Euphorbiaceae, Sterculiaceae, Olacaceae and Rubiaceae .Mean
number of stems per hectare ranges from 400.44 to 1134.0 for the small trees (5-20cm dbh); 89.78 to
174.25 for the medium trees (20-40cm dbh) and 8.33 to 17.06 for the large trees (> 40cm dbh) Mean
basal area per hectare ranges from 4.94m2 to 8.81m2 for the small trees, 5.4m2 to 9.63m2 for the
medium trees and 4.64m2 to 9.04m2 for the large trees.
Inverse of Simpson diversity indices range between 15.1 to 16.27 for the small tree, 13.43 to 16.37 for
the medium trees and 23.44 to 26.34 for the large trees. The highest mean values per hectare of these
parameters were found in 1987 enumeration, while the least values were found in the year 2000
enumeration. This variability may not be due only to the number of plots available for enumeration
alone, but also as a result of poaching in the remaining plots before the 2000 enumeration. The study
recommends that conscious efforts should be made to protect and maintained the permanent sample
plots not only to reduce the possibility of encroachment but also to achieve the objective for which
they were established which was to elucidate the dynamics and growth pattern of the natural
rainforest. There is also a need for international assistance to achieve this.