A review of previous evaluations of long-term changes in treated Nigerian rain forest is presented, to show that these studies have concentrated on economic species with little consideration of other species, or of forest biomass and structure.We examine regeneration and successional patterns in Omo Forest Reserve by comparing enumeration data taken before (1952) and after (1981) treatment of the forest by selective canopy opening and climber-cutting (Plot A), or clear-felling and burning (Walsh system) (Plot C).Before treatment, about 50 species in 25 families were found of stems ≥10 cm dbh, in 4.05 ha of the forest, the Euphorbiaceae contributing the greatest number of species while the medium-sized trees Diospyros alboflavescens (Ebenaceae) and Strombosia pustulata (Olacaceae) contributed more than 40% of the stems.Twenty-eight years after treatment (1981) the number of species and families remained similar to those in 1952, although smaller areas (0.75 ha) were enumerated; the treated plots were, however, dominated by early succession species such as Macaranga barteri, Musanga cecropioides, Cleistopholis patens, Funtumia elastica and Fagara macrophylla, and lacked an abundance of the ‘economic’ species that treatment had been expected to induce; the medium-sized trees that were dominant in 1952 were still abundant in Plot A but not in Plot C.For stems ≥ 30 cm dbh tree diversity (reciprocal of Simpson's index) was highest (15.7) in a 1952 plot and least (4.8) in the clear-felled plot enumerated in 1981; diversity of the 1952 plots, however, fell markedly to values lower than those for the 1981 plots when computation was based on all stems ≥10 cm dbh, presumably because of increase in abundance of small-stemmed species like Diospyros spp., Strombosia sp. and Rinorea sp., each represented by a large number of stems.Basal area was greatest (29.6 m2 ha−1) in the 1952 plots and least (12.7 m2 ha−1) in the clear-felled plots enumerated in 1981, but the relative distribution of basal area and number of stems in size-classes was similar in all the plots.Mean annual increment, computed by dividing the mean diameter (7.50 cm) of the stems in the clear-felled plots by the number of years (28) over which they had grown, was 0.27 cm.Nauclea diderrichii dominated the seedling regeneration from the first year after clear-felling and burning (1954) till the sixth year (1960), when seedlings of the Meliaceae entered the regeneration list and overall seedling density was 395 per hectare.Among the plots assessed in 1981, the standing crop was greatest in an untreated Control plot (229.6 t ha−1) followed by Plot A (159.7 t ha−1) and Plot C (91.1 t ha7−1), but the relative allocation of biomass to stem, branch, leaf, root and fruit fractions was comparable for all plots.The data are discussed in relation to other Nigerian forest studies and it is suggested that the main qualitative features of structural organization and the species composition of the top canopy synusia of mature secondary rain forest may be determined quite early in the development of the stand.

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To up-date and extend knowledge of the Akure Strict Natural Reserve an assessment, block by block, of forest in the core of the Inviolate Plot was undertaken in 1974 and complemented with soil sampling. Principal components analysis indicated a gradient of soil reaction and available phosphorus through the core of the plot. Ordination (DECORANA) of floristic data revealed that a floristic trend paralleled the soil trend. In the vicinity of a drainage line, at the western end of the core, soils were lower in available phosphorus, more acid, sandier and texturally more uniform with depth. Typical trees of ferralsols were prominent on these soils but were replaced by species of ferric luvisols, especially members of the Sterculiaceae, on soils of superior nutrient status towards the eastern end. It is suggested that the soil gradients were not effects produced by the trees.Comparison of a 1946 data set with the 1974 data supported the view that the forest had been structurally and floristically stable over the interval between assessments. This is considered justification of the original choice of the area as a Strict Natural Reserve representative of high forest in this part of Nigeria.

The diversity of trees 5 cm in diameter and above at breast height was studied at five sites within the Nigerian rainforest. The sites were Gambari, Oban, Omo, Owan and Sapoba forest reserves. Diversity was measured in terms of similarity and heterogeneity and explored at beta and gamma levels. Over 315 species were encountered during the study. In terms of species richness, there are 80, 226, 163, 137 and 159 species in Gambari, Oban, Omo, Owan and Sapoba, respectively. The occurrence of the species showed that, while 26 species are common to all the sites, 62, 17, 15, 8 and 6 species are restricted to Oban, Omo, Sapoba, Gambari and Owan, respectively. Ordination by detrended correspondence analysis indicated gradients along the first two axes. The first axis reflecting rainfall gradient which decreases from Oban through to Sapoba, Owan and Gambari. The second axis showed a separation of Omo, and Owan and Sapoba. This suggests a gradient of soil parent materials, the former site is on the basement complex while the latter is on the cretaceous rock. It is suggested that each forest should be managed based on its particular characteristics, such as species composition and abundance. Thus, forests with high species diversity but fewer numbers of individuals, such as in Oban, should be earmarked for conservation while species-rich forests with relatively more economic species, as in Sapoba and Omo, should be managed for sustained timber production. Floristically poor forest, such as those in Gambari and Owan, should be converted to plantations of fast growing species but with care taken to avoid exposing such sites to soil erosion.

The need to conserve representative samples of natural vegetation was recognized in Nigeria over thirty years ago. Before 1950 only two conservation areas had been laid down but at present there are seven in operation. Most of them are between 60 ha (ca 1/4 sq. mile) and 350 ha (ca 12/5 sq. miles) in area, and together they include at least one example of each major ecological type occurring in the country.There are difficulties in constituting and safeguarding conservation areas, particularly outside State Forest Reserves. While it is to be hoped that legislation will soon be introduced to facilitate protection, a comprehensive survey has recently been carried out with a view to substantially increasing the number of conservation areas in Nigeria, and to make them more fully representative of the different vegetation zones of Nigeria.Work is also proceeding towards determining the optimum size for each area within the different vegetation types. It is hoped to be able to establish up to 40 conservation areas within the next 2 years, and ultimately as many as 110 may be designated.