Tree population changes in treated rain forest at Omo Forest Reserve, south-western Nigeria

• Published in: Journal of tropical ecology 1987-11, Vol.3 (4), p.291-313
• Main Authors: Okali, D. U. U., Ola-Adams, B. A.
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; dominant species; Forest canopy; forest dynamics; Forest management. Stand types and stand dynamics. Silvicultural treatments. Tending of stands. Natural regeneration; Forest regeneration; Forest reserves; Forest stands; forest succession; forest trees; Forestry; Fundamental and applied biological sciences. Psychology; natural regeneration; Nigeria; Population dynamics; rain forest; Rain forests; silvicultural systems; silviculture; species; species composition; Stand types and stand dynamics. Silvicultural treatments. Tending of stands. Natural regeneration; Stems; Tillage; tree classes; tree populations; Trees; Tropical rain forests
• ISSN: 0266-4674; 1469-7831
• DOI: 10.1017/S0266467400002297

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 dens