Effects of exotic tree plantations of teak (Tectona grandis) and gmelina (Gmelina arborea) on a forest soil in south‐western Nigeria
ABSTRACT The properties of soil under 15-year-old plantations of gmelina (Gmelina arborea) and teak (Tectona grandis) were compared with logged forest soil in south-western Nigeria. The soil was significantly denser in the 0–10 cm layer of plantation soil and total porosity less than that of forest soil. Organic carbon was significantly greater in the 0–10 cm layer of forest soil. Similarly, the concentrations of total N, exchangeable Ca, Mg and K were greater under forest soil, but the concentrations of available P were similar under all three ecosystems. The smaller organic carbon and nutrient content of plantation soil is mainly due to its more open organic matter and nutrient cycles and nutrient immobilization in the fast-growing exotics.
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ABSTRACT: This paper examines the depletion of Nigeria's natural forest resources consequent upon exploitation without adequate conservation. It also examines plantation forestry as the government's strategy for replenishing the country's lumber resources. It argues that it is ecologically unwise to clear-fell reserves of native rain forest and replant them with monoculture tree plantations, especially of the exotics, teak and gmelina, and stresses the need to conserve the rain forest ecosystem in southern Nigeria.The Environmentalist 01/1990; 10(2):127-134.
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ABSTRACT: Aim The effects of planted forests on soils are of great concern in the context of the increasing demands for timber production and atmospheric CO2 sequestration. However, the effects of plantations on soil properties have not well been quantified. We determined the effects of plantation practice on soil properties based on a comparison between natural forests and plantations.Locations All the continents except for Antarctica.Methods The meta-analysis approach was used to examine the differences in 14 soil variables in the mineral layer, including pH, bulk density, C, N, P, K, Ca, Mg, Na and Al concentrations, C/N ratio, cation exchangeable capacity, base saturation, and moisture between plantations and their adjacent natural forests from 73 published studies.Results Plantations did not differ from natural forests in soil pH or soil Na and Al concentrations. Soil bulk density below plantations increased by 12.5%, and soil C and N concentrations decreased by 36.0% and 26.5%, respectively, relative to natural forests. The other eight variables were 8.4–30.6% lower in plantations than in natural forests. The general patterns also held true for planted trees from the genus Pinus and for study regions in China. The patterns for soil bulk density and C and N concentrations were not different between the two groups in relation to various factors: stand age (< 25 years versus ≥ 25 years), leaf form (broadleaved versus coniferous) and leaf seasonality (deciduous versus evergreen), tree species origin (native versus exotic), land-use history (afforestation versus reforestation) and site preparation for plantations (burnt versus un-burnt treatment), and biogeographic zone (tropical versus temperate).Main conclusions Our results suggest that the level of soil fertility in plantations is unlikely to restore to the level in natural forests, implying that the replacement of natural forests by plantations may be a practice best avoided to maintain the ecosystem sustainability.Global Ecology and Biogeography. 06/2011; 21(3):318 - 327.