Forest-savanna Zone Research Articles

Profile of eye lesions and vision loss: a cross-sectional study in Lusambo, a forest-savanna area hyperendemic for onchocerciasis in the Democratic Republic of Congo.

To determine baseline data regarding eye lesions and vision loss in five villages of Lusambo, an onchocerciasis-hyperendemic forest-savanna area in the Democratic Republic of Congo (DRC), in preparation of mass ivermectin distribution. Five villages were selected by simple randomization. Through a cross-sectional design, 750 subjects were examined ophthalmologically. The eye examination included acuity visual measurement, slit-lamp examination, ophthalmoscopy, intraocular pressure measurement, and visual field assessment by the Wu-Jones test. There was a high prevalence of onchocerciasis-related eye lesions compared with non-onchocercal lesions. Chorioretinitis (20%) was the most frequent disease, others were punctate keratitis and microfilariae in the anterior chamber in equal frequency (13.8%), white intraretinal deposits (10.4%) and iridocyclitis (8%). Vision loss was discovered in 8.5% of the subjects, of whom 0.5% had bilateral blindness, 2.2% had monocular blindness and 5.7% had visual impairment. Vision loss was mostly caused by onchocerciasis-related diseases, especially those affecting the anterior segment of the eye. Features of ocular onchocerciasis usually described in forest and savanna areas were both found in this forest-savanna zone of the DRC.

AN IMPROVED COVER CROP-FALLOW SYSTEM FOR SUSTAINABLE MANAGEMENT OF LOW ACTIVITY CLAY SOILS OF THE TROPICS

The potential of planted leguminous cover crop fallow as an alternative to the natural regrowth fallow for sustaining the productivity of low activity clay (LAC) soils in the tropics as the fallow period shortens was tested at Ibadan in the forest-savanna zone of southwestern Nigeria. The study, initiated in 1990, compared an improved system (cover crop-fallow) and a traditional system (natural fallow), with the aim of developing an improved cover crop-fallow system for sustainable management of LAC soils of the tropics. Pueraria phaseoloides, an herbaceous, N-fixing, perennial legume with a slow initial growth habit, was selected as a test cover crop. Pueraria was sown with a maize-cassava intercrop at the same season. In a 2-year cycle, 1 year of cropping was followed by 1 year fallow with pueraria for the cover crop-fallow system or with natural regrowth (mainly Chromolaena odorata) for the natural fallow system. Maize-cassava intercropping without a fallow period (continuous cropping) was included as a control. No fertilizer was applied throughout the experimental period. Pueraria produced 253 kg N ha -1 after the fallow period, compared with 109 kg N ha -1 for chromolaena; pueraria was also better in recycling P (11 kg P ha -1 ) than was chromolaena (9 kg P ha -1 ). Natural fallow for 1 year increased the maize yield from 75 to 350% from 1992 to 1996, and the cassava yield from 9 to 130% compared with continuous cropping. Cover crop-fallow resulted in a 22 to 72% higher maize yield than the natural fallow from 1992 to 1996. Although in 1992 and 1994 cassava tuber yield was lower with the cover crop-fallow than with the natural fallow, with better pueraria husbandry in 1996, cover crop-fallow increased the cassava tuber yield by 41%. With residue burning, the N balance was 27 kg N ha -1 yr -1 for the pueraria cover crop-fallow system and -15 kg N ha -1 yr -1 for the chromolaena natural fallow system. Cover crop-fallow maintained soil organic carbon status better than the natural fallow. Integration of a pueraria legume cover crop did not affect soil pH. Results indicate cover crop-fallow with pueraria could be a better alternative to traditional natural fallow under shortened fallow periods for raising or maintaining productivity of LAC soils of the humid tropics.

The causes and profile of visual loss in an onchocerciasis-endemic forest-savanna zone in Nigeria

In an onchocerciasis-endemic forest-savanna mosaic zone of southeastern Nigeria, blindness was found in 5.4% of 1,217 people who voluntarily attended for examination from a population of 14,000. Apart from cataract, the most important causes of blindness in the area were eye diseases that are known to be associated with onchocerciasis. Refractive error, although a non-onchocerciasis-related eye defect, was the number one cause of visual loss found in the study. The causes of blindness in our examined population are similar to what is found in onchocerciasis-endemic areas of the savanna zone and dissimilar from those found in the forest zone. In this forest-savanna mosaic zone, the prevalence of onchocerciasis was higher in the respondents with poor vision than in those with adequate vision. Similarly, low vision was found to be more common in people with high microfilarial loads, but people with high loads also tended to be older than those with moderate or low microfilarial loads, which might suggest that low vision was only a function of age. Nonetheless, analysis of our data shows evidence of an association between low vision and microfilarial load in adults aged 60 years and above. It is concluded that onchocerciasis in the forest-savanna mosaic zone of Nigeria has the features until recently associated only with savanna onchocerciasis, and that this should be taken into consideration in planning and executing onchocerciasis control programs in the area.

Evaluation of six cultivars of white yam (Dioscorea rotundata) across three yam-growing areas in southeastern Nigeria

SUMMARYA split split-plot experiment was conducted in the 1986 and 1987 cropping seasons in three major yam-growing areas in southeastern Nigeria to assess the performance and yield stability of six cultivars of white yam (Dioscorea rotundata Poir). Location, fertilizer and cultivar, as well as some of their interaction effects, significantly affected tuber yields.The best location for yam production, based on the overall performance of the cultivars, was the sub-humid Guinea savanna, followed by the humid forest-regrowth and then the transitional forestsavanna zone. Except for two cultivars, which performed best in their source locations, all other cultivars yielded best at a different location. Thus, at present, these cultivars are not grown in those areas to which they are best suited. This makes it desirable to test exogenous cultivars in new areas. In terms of yield stability, however, the two cultivars originating from the humid forest-regrowth area gave the most stable yields across the three diverse environments considered. Although they did not give the highest tuber yields at all the locations, their overall yields were above the mean yields forall the cultivars. The most suitable cultivars were recommended for each ecological zone, on the basis of the observed interaction effects.

Production pressure and environmental change in the forest-savanna zone of Southern Ghana

This study confirms the view that changes in the biophysical environment are significantly related to production pressure. The scattered concentrations of forest species in Ghana's forest-savanna zone evidently are relics of a dominant natural forest. Deforestation has entailed environmental quality deterioration, including biodiversity loss, and impoverishment of the soils. Farmers try to counter environmental change by modifying cropping and intensifying production, but without much success because of poverty and tenurial and technological constraints. Associated with population and market pressures for production, the change calls for greater attention to sustainable small farmer environmental management systems.

Persistence and recovery of introduced Rhizobium ten years after inoculation on Leucaena leucocephala grown on an Alfisol in southwestern Nigeria

Establishment of Leucaena leucocephala was poor at Ibadan (Transition forest-savanna zone) and Fashola (savanna zone, 70 km north of Ibadan) in southwestern Nigeria as a result of low soil fertility and the presence of only a few native rhizobia capable of nodulating it. Inoculation with L. leucocephala at these two locations in 1982 resulted in striking responses with Rhizobium strains IRc 1045 and IRc 1050 isolated from L. leucocephala grown in Nigeria. The persistence of inoculated effective Rhizobium strains after inoculation is desirable since it removes the need for reinoculation. Because of the perennial nature of L. leucocephala and its use in long-term alley farming experiments, we examined the persistence of inoculated rhizobial strains after inoculation, and their ability to sustain N2-fixation and biomass production at Ibadan. In 1992, ten years after Rhizobium introduction, uninoculated, L. leucocephala fixed about 150 kg N ha-1 yr-1 or about 41% of total plant N compared to 180 kg N ha-1 yr-1 or 43% measured in 1982. Serological typing of the nodules using the Enzyme-Linked-Immunosorbent Assay (ELISA) and intrinsic resistance to the streptomycin test revealed that most of the nodules (96%) formed on L. leucocephala in 1992 were by Rhizobium strains IRc 1045 and IRc 1050, which were inoculated in 1982. Nodules were absent on uninoculated L. leucocephala grown on the adjacent field with no history of L. leucocephala cultivation. We conclude that the N2 fixed by Rhizobium strains IRc 1045 and IRc 1050 persisted for many years in the absence of L. leucocephala and sustained effectively fixed N2 which growth and yield of L. leucocephala after several years, thus encouraging a possible low-input alley farming system by smallholder farmers in Nigeria.

A catenary approach to the study of gravel layers and tropical landscape morphodynamics

Summary Relationships between landsurface morphology and surficial geology have been examined in the forest-savanna zone of Sierra Leone. Landforms identified by morphometric surveys along ten interfluve crest to valley floor transects were sampled by pitting down to bedrock. Each landform had a gravel layer (“stone line”) with a characteristic average depth, texture and petrographic composition. Examining the variations in gravel layer petrology within a catenary framework gave insights into the contemporary morphodynamics of the study areas, particularly the transfer, storage and removal of materials from the valley systems. Palaeoenvironmental indicators were also found that enable the landscape evolution of this region to be more fully understood.