Effects of exotic tree plantatins of teak (Tectona grandis) and gmelina (Gmelina arborea) on a forest soil in south-western Nigeria

Department of Geography, University of Ibadan, Nigeria.
Soil Use and Management (Impact Factor: 1.47). 01/2007; 6(1):43 - 45. DOI: 10.1111/j.1475-2743.1990.tb00796.x


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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    • "However, plantations can potentially alter the biogeochemical cycles of ecosystem as a consequence of changes in tree species composition when compared with their adjacent natural forests (e.g. Aborisade & Aweto, 1990; Wall & Hytönen, 2005; Freier et al., 2010) and the intervention of silvicultural activities (e.g. Yang et al., 2005; Zheng et al., 2008). "
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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.
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    ABSTRACT: Blue gum (Eucalyptus globulus) plantations are managed as a successive short rotation coppice system for more than a century in the central Ethiopian highlands. Consecutive cutting cycles of these plantations may alter forest site productivity, soil physico-chemical properties, and forest floor environment. To test this hypothesis, ten plantations ranging from 11-60 years (2-10 cutting cycles), with 1, 4, 5, 7 and 9 years old coppice-shoots were selected in the central highlands of Ethiopia, where the most extensive and oldest Eucalyptus plantations exist within the country. The thesis summarizes the temporal dynamics of above-ground biomass and nutrient partitioning (Paper I & II), soil physical and chemical properties (Paper III), ground flora composition and diversity (Paper IV) in a number of Eucalyptus globulus plantations along a chronosequence. Mean above-ground biomass ranged from 11 to 153 ton ha-1 in 1 and 9 year old plantations, respectively. In contrast, above-ground biomass production declined markedly across the total plantation ages (cutting cycles). On average, stand biomass production was reduced by 14% from the second and third cutting cycles to the sixth and seventh cycles, and by a further 86% from the second and third to the tenth cutting cycles. Although non significant, a similar declining trend was observed for the vegetation cover, species composition and diversity of the ground flora in consecutive cutting cycles. The macro-nutrient concentrations (N, P, K, Ca and Mg) in above-ground tree biomass showed significant differences between tree components. The nutrient concentrations (N, P, K, Ca and Mg) were highest in foliage, while the lowest concentrations were obtained in stemwood and branch tree parts. The nutrient content (kg ha-1) followed the order: leaves > stemwood > stembark > twigs > branches. For most components, neither coppice-shoot age nor cutting-cycle number had a significant influence on the macronutrient concentrations. Although not significant, a decreasing nutrient concentration trend was generally observed with the coppice-shoot age. Soil nutrient concentrations (N, Ca and Mg) showed a statistically significant decline with the advancement of cutting cycles. Thus, the soil nutrient stock (kg ha -1) in the tenth cycle was the poorest of all the stands. The reduction of macronutrient stock in consecutive cutting cycles appears to be related to repetitive harvests in short rotations, whole-tree harvesting and nutrient loss caused by complete forest litter removal. Hence, deleterious anthropogenic practices associated with consecutive cutting cycles may eventually lead to yield decline and forest site degradation on a long-term basis. Therefore, it can be suggested that with appropriate silvicultural and management interventions, it could be possible to mitigate site quality decline over the successive cutting cycles of Eucalyptus plantations. For long-term site quality and sustainability of biomass production, prolonging the length of cutting cycles, and prohibiting or controlling recurrent litter raking appears to be imperative, because these practices may jeopardize the sustainable management of Eucalyptus globulus plantations in the central highlands of Ethiopia.
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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.
    No preview · Article · Jan 1990 · The Environmentalist
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