Forest Zone Of West Africa Research Articles

Evaluation of sub-acute oral toxicity effects of Phaulopsis falcisepala C.B. Clarke (Acanthaceae) in rats

Phaulopsis falcisepala is a herb or undershrub found in forest zone of West Africa and used for a wide range of ethnomedicinal purposes. Despite the ethnomedicinal importance of P. falcisepala, detailed data about its safety and toxicity is lacking. This study was done to evaluate sub-acute toxicity of P. falcisepala in rats. Whole plant of P. falcisepala was extracted with methanol. Wistar rats (n = 6/group) were administered orally with P. falcisepala extract at doses of 250, 500 and 1000 mg/kg/day for 28 days. Control group received distilled water. Physical observations were recorded daily and weights of animals were recorded weekly. After 28 days, samples of blood, serum and vital organs were obtained for haematological, biochemical and histological evaluations. Results showed that daily oral doses of P. falcisepala extract up to 1000 mg/kg for 28-days did not cause any behavioral changes or mortality. The plant extract did not induce significant alterations in body-weights, haematological, hepatic and renal parameters and serum levels of sodium, potassium, and chloride ions. No significant differences (p > 0.05) were recorded in relative weights of ovaries, testes, heart and kidneys of experimental groups compared to control group. Changes were observed in lipid profile (p < 0.05) and histology of kidneys and liver of rats treated with plant extract, particularly at highest dose, 1000 mg/kg. These findings suggest that extract of P. falcisepala could be safely applied for its medicinal properties at low to medium doses. However, sub-acute administration of doses up to 1000 mg/kg/day could pose deleterious risk to liver and kidneys.

Loop-migration and non-breeding locations of British breeding Wood Warblers Phylloscopus sibilatrix

ABSTRACT Capsule: British breeding Wood Warblers Phylloscopus sibilatrix show a clockwise loop migration incorporating stops in southern Europe, the Sahel, and the humid forest zone of West Africa. Aims: To determine autumn and spring migration routes, the location and duration of stopover sites on migration, and the location of non-breeding areas of British breeding Wood Warblers. Methods: In 2016 and 2018 we deployed geolocators to male Wood Warblers on Dartmoor, Devon, and in the New Forest, Hampshire. We retrieved four geolocators from returning birds in 2017, 2019, and 2020. Results: Male Wood Warblers departed breeding sites in late July and stopped for most of August in central southern Europe, crossed the Sahara by a non-stop night and day flight immediately followed by a short stop, and then migrated west to a longer stopover in the Sahel. Final non-breeding destinations were in an area of West Africa covering Guinea, Sierra Leone, and Liberia. Two were tracked on spring migration, again crossing the Sahara via a non-stop flight before migrating through Western Europe to complete a clockwise loop migration back to Britain. Conclusion: All tracked Wood Warblers used stopovers for at least three weeks in three distinct regions, in central southern Europe, in the Sahel, and in the humid zone of West Africa. Although the limitations of geolocation prevent matching locations with habitat, these regions are broadly characterized by distinct forest or woodland habitat types, which differ from breeding habitat. All four tracks showed similar patterns in route, stopover behaviour, and timings, suggesting they may be representative of males in these breeding populations, and potentially of other British and western European Wood Warbler populations.

Soil fertility status of soils of Sudano-Sahelian and Humid Forest Zones of West Africa and some soil management strategies for smallholder farms

Knowledge of soil properties and fertility status of farmers’ fields are basic information needed by Agricultural Extension Agents to guide farmers on wise and sustainable management of soil. The properties of some cultivated fields in the Sudano-Sahelian of Ghana and Humid Forest zones of Nigeria were studied. The aim was to quantify the soil properties and fertility status with a view to prescribing low input ecological technologies that would improve and sustain soil productivity. Core samples were taken from the depth of 0 – 40 cm in eleven and eight farmers’ fields in the Upper East Ghana and South East Nigeria, respectively. Soil properties determined using standard methods were; pH, TN, SOC, SOM, P, Exchangeable bases, EA, base saturation, PSD, WP, FC, bulk density, P and SHC. Both soils were sand in texture (> 700 g kg-1). The WP and FC were either below or within the lower border of critical levels. This shows crops in all the fields are prone to incipient wilting under any short dry spell. The chemical properties of the Sahelian-Sahelian zone showed that pH averaged 6.54 (moderate acidic), SOC 16 g kg-1 (low), TN 13 g kg-1 (very high), P, 18 mg kg-1 (moderate), K 0.23 C mol kg-1) (moderate), ECEC 8.18 C mol kg-1(medium fertility class). In the Humid Forest zones, pH was 4.38 (extremely acidic), SOC 7.41 g kg-1 (very low), N 1.78 g kg-1 (low), P 15.94 mg kg-1 (moderate), K 1.94 C mol kg-1 (very high) and ECEC 8.8 C mol kg-1 (medium fertility class). The fertility class indicates that the soils will response to external inputs and wise land management practices. A mix of Arbuscular mycorrhizal fungus (AMF), multipurpose tree species, contour cultivation, organic mulch, multiple crop mixture, under vetiver grass buffer strip is recommended.

Effect of Phaulopsis falcisepala (Acanthaceae) Leaves and Stems on Mitotic Arrest and Induction of Chromosomal Changes in Meristematic Cells of Allium Cepa

Phaulopsis falcisepala is an herb found in the forest zone of West Africa. It is applied ethnomedicinally for treating wounds and cancer. This study investigated the chemical constituents, cytotoxicity, and antimitotic activity of P. falcisepala leaves and stems. Chemical constituents were evaluated using phytochemical methods. Cytotoxicity was investigated using brine shrimp lethality and Allium cepa root growth inhibition assays. Antimitotic activity and induction of chromosomal aberrations were assessed by cytological examination of treated A. cepa meristematic cells. Chemical investigation revealed the presence of diverse bioactive chemical groups, including alkaloids, terpenoids, tannins, flavonoids and saponins in various extracts of the leaves and stems of P. falcisepala. Aqueous and methanol extracts contained copious amounts of the phytochemicals while ethyl acetate and n-hexane extracts contained moderate to trace amounts. The extracts demonstrated toxicity against brine shrimps, with LC50 values in the range 13.1–52.2 µg/mL. The extracts significantly inhibited A. cepa root growth, with IC50 values in the range 63.91–87.4 µg/mL and 45.34– 81.15µg/mL for 24 and 48 h treatments. The extracts (IC50 values in the range 46.2–94.23 µg/mL and 30.79–75.81 µg/mL for 24 and 48 h treatments) produced significant antimitotic effect comparable to or greater than that of methotrexate (IC50 value >125 µg/mL). Cytological examinations revealed that the extracts induced mitotic arrest and chromosomal changes. This study reports for the first time the phytoconstituents and cytotoxic activity of P. falcisepala supporting its ethnomedicinal use and could serve as the basis for further pharmacological studies and isolation of bioactive principles.

Phytochemistry, nutritional composition, and pharmacological activities of Thaumatococcus daniellii (Benth): a review.

Thaumatococcus daniellii (Benth) is a member of a diverse family of plants known as Marantaceae. Native to the tropical forest zones of West Africa, the plant is globally famous for its low calorie, nondiabetic natural sweetener called thaumatin found in its aril. T. daniellii thrives in deep shade, and it is used locally as a taste modifier and for preparing fish traps, ornamental bags, and mats. Organs of the plant are used in folkloric medicine as a laxative and in treating ailments such as mental disorders, high blood sugar, and lung diseases. The seeds and leaf sap are potent as an antidote against snake venom and bee stings and for preventing dystocia and prolonged child labor. Proximate analysis, phytochemical screening, and gas chromatography-mass spectrophotometry revealed that the plant contains proteins, important macro- and microelements (calcium, magnesium, zinc, sodium, phosphorus, potassium, iron, and manganese), and abundant active principles and compounds such as squalene tannin, alkaloids, saponins, epicatechin, steroids, phlobatannins, anthraquinones, terpenoids, spartein, ribalinidine, rutin, phytic acid, and kaempferol. Biological activities include hypolipidemic, antihyperglycemic, antioxidant, insecticidal, bioremediative, and antimicrobial activities. T. daniellii could be used in the formulation of food supplements and drug development.

The contributions of C. F. Charter to tropical soil survey and classification

Cecil Charter had taught botany and biology in China and Antigua for five years, when in 1931 he was engaged to conduct a soil survey of the sugarcane-growing areas of Antigua. This was followed by similar surveys elsewhere in the Caribbean. In 1944, he joined the West African Cacao Research Institute in the Gold Coast (now Ghana) to carry out soil investigations in the forest zones of West Africa. In 1949 he moved to organise the soil survey unit in the Gold Coast Department of Agriculture, and, in 1951, to found and direct the new Soil and Land Use Survey Department. He rapidly built up a highly professional unit that produced many practical and useful reports of high quality. He based the surveys on ecological principles, selecting river basins as mapping regions. In the initial absence of qualified soil scientists, he subdivided the soil survey process and trained school leavers as technicians for separate tasks. Teams of these technicians examined soils, vegetation and land use at regular intervals on regularly-spaced traverses cut across the topography. Charter’s contributions to soil science included his recognition of non-residual tropical soils formed in material brought to the surface by soil fauna and treefall. Also, he differentiated between highly acidic upland Oxysols in high-rainfall areas, which he considered unsuitable for cocoa cultivation, and less acidic Ochrosols, which were more suitable. Based on farmers’ experience and his ecological background, he differentiated between forest, thicket and savannah soils within these groups. He strongly advocated genetic and contextual classification of tropical soils.

Effect of multipurpose trees and shrubs on degraded mined‐out soil in a semi‐deciduous forest zone of West Africa

AbstractMultipurpose trees and shrubs (MPTS) establishment plays important role in accelerating natural restoration and productivity of degraded soils for ecosystem stability, biological diversity, and most importantly for agricultural uses. Multipurpose tree plantation with a mixed stands of Leucaena leucocephala, Albizia zygia, Faidherbia albida, Acacia auriculiformis, Senna siamea, Azadiractha indica, and Gliricidia sepium was established to reclaim degraded mined‐out Ferric acrisol in a semi‐deciduous forest zone of Ghana, West Africa. The main aim of the study was to evaluate the effects of the age of MPTS on some physical and chemical properties of degraded mined‐out soil of the Oweri Mines Company, Ltd., Konongo (6°37′56.8″N, 1°13′39.02″W). The study determined soil total nitrogen (tN), soil organic carbon (SOC), acidity (pH), aluminum (Al), arsenic (As), and mercuric (Hg) contents and the relationship between these soil parameters. Soils were sampled at two depths: 0–30 and 30–60 cm from four different age groups of MPTS plantation: non‐reclaimed (NR), 5‐year‐old MPTS plantation, 10‐year‐old MPTS plantation, and adjacent undisturbed natural forest (NF). The pH, SOC, tN, Al, As, and Hg contents and bulk density were significantly influenced by age of MPTS plantation. The 10‐year‐old MPTS soil had 53%, and the NF soil had 57%, higher SOC than NR soil. Soil tN in the top 0–30 cm depth for the 5‐year‐old was 33%, 10‐year‐old MPTS was 59%, and the NF was 69%, higher than tN in the NR soil. Whereas soil pH had positive significant relationship with soil Hg and As, the reverse was observed with soil Al content.

A Review on Ethno-Medicinal and Pharmacological Activities of Sphenocentrum jollyanum Pierre.

Sphenocentrum jollyanum Pierre is a member of a diverse family of plants known as Menispermaceae. They are famous for a plethora of important biological functions. S. jollyanum is a shrub native to the tropical forest zones of West Africa and thrives in deep shade. It is widely cultivated in Cameroun, Sierra Leone, Nigeria, Ghana, and Côte d’Ivoire. S. jollyanum is employed in folk medicine as a cure for wounds, fever, coughs, high blood pressure, breast tumor, constipation, and as an aphrodisiac. Phytochemical investigations revealed that the plant is a rich source of secondary metabolites such as annin, alkaloids, saponins, and flavonoids. Pharmacological activities include anti-diabetic, anti-inflammatory, anti-bacterial, anti-viral, anti-malarial, angiogenic, and anxiogenic. Thus, this present review summarizes the phytochemical and nutritional constituents and important biological studies on various crude extracts, fractions, and isolated principles of all morphological organs of S. jollyanum.

Occurrence, distribution and health risk from polycyclic aromatic compounds (PAHs, oxygenated-PAHs and azaarenes) in street dust from a major West African Metropolis

Scientific evidence suggests that the burden of disease on urban residents of sub-Saharan African Countries is increasing, partly as a result of exposure to elevated concentrations of toxic environmental chemicals. However, characterization of the levels, composition pattern and sources of polycyclic aromatic compounds (PACs) in environmental samples from African cities is still lacking. This study measured the PAHs, oxygenated-PAHs (OPAHs) and azaarene (AZAs) content of street dusts collected from Kumasi, Ghana (a major metropolis located in the tropical forest zone of West Africa). The ∑Alkyl+parent-PAHs, ∑OPAHs and ∑AZAs concentration in street dust averaged 2570ngg−1 (range: 181–7600ngg−1), 833ngg−1 (57–4200ngg−1) and 73ngg−1 (3.3–240ngg−1), respectively. The concentrations of ∑Alkyl+parent-PAHs were strongly correlated (n=25) with ∑OPAHs (r=0.96, p<0.01) and ∑AZAs (r=0.94, p<0.01). The ∑OPAHs concentrations were also strongly correlated with ∑AZAs (r=0.91, p<0.01). Concentrations of individual PAHs in these street dusts were enriched at between 12 and 836 compared to their average concentrations in background soils from same city, demonstrating the high influence of traffic emissions. Several individual OPAHs and AZAs had higher concentrations than their related and often monitored parent-PAHs. The estimated incremental lifetime cancer risks due to the parent-PAHs in street dusts was >10−6 indicating high risk of contracting cancer from exposure to street dust from Kumasi. The contribution of OPAHs, AZAs, and alkyl-PAHs in street dust to cancer risk could not be quantified because of lack of toxicity equivalency factors for these compounds; however this could be significant because of their high concentration and known higher toxicity of some polar PACs and alkyl-PAHs than their related parent-PAHs.

THE CIVILIZATIONS OF THE YAM: INTERRELATIONSHIPS OF MAN AND YAMS IN AFRICA AND THE INDO‐PACIFIC REGION

Τ Τ appears at first sight remarkable that the term le civilization de Tignarne -*should have been used independently by different authors to describe two farseparated areas of human culture. In West Africa the term was first used by Miege (1954) to describe the more easterly part of the forest zone of West Africa, between the Bandama River in central Ivory Coast and the Cameroon Mountain chain ; and between the drier parts of the savanna, around 8°-io° N. and the sea with its bordering swamps and lagoons. This area, also described as the West African Yam Zone (Coursey, 1965, 1967) depends for its staple food supplies on root and tuber crops, especially yams (Dioscorea spp.), in contrast to the areas to the north, where sorghums and millets provide the major staples, and to the west, where upland rice (Oryza glaberrima Stapf.) is dominant. The identical term has been used in the Pacific Ocean context (Haudricourt, 1964) to refer to at least parts of that area, based on Papuo-Melanesia but extending far out into the Pacific Ocean, where yams are major staple foods. The concept has been developed by Barrau (1963, 1965), the delimitations of this area of the Indo-Pacific being essentially as indicated by him. There are many differences between these two areas of the world, which outweigh the similarities. Nevertheless, on closer examination the application of this term to both is less surprising than it seems at first ; for in both the basis of the civilization is, in fact, the cultivation of yams. The introduction of new crops, especially sweet potato, Ipomoea batatas (L.) Lam. and cassava (Manihot esculenta Cranz.), and others of American origin, in recent times, has reduced the dominance of yams as the material basis of the subsistence of the people, but in former times in some places within living memory yams provided substantially the greater part of the staple food. This was reflected in both these areas in the large volume of ritual and magico-religious practices associated with almost every aspect of yam cultivation and storage. These civilizations were then based on the yam not only in a material sense ; the crop was also fundamental to the cultural life of the people, to at least as great a degree as were the grain crops in Mediterranean and Asiatic cultures. To those who have received their scientific education within the framework of the cultural heritage of Europe and the Mediterranean world as have virtually all

Nutrient constraint of rainfed rice production in foot slope soil of Guinea Forest in Côte d’Ivoire

Soil nutrient deficiencies can affect rice yield and grain mineral content wherever they occur, but an understanding of their effect on upland rice production in humid forest zone of West Africa is still limited. Therefore, a nutrient omission trial was conducted on foot slope soil in 2003, 2004 and 2005 in Côte d’Ivoire using rice variety WAB 56–104. The effect on rice grain yield (GY) and nutrient content of complete fertilizer (Fc with nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and zinc (Zn)) was compared with Fc from which a specific nutrient was excluded (Fc – N, Fc – P, Fc – K, Fc – Ca, Fc – Mg and Fc – Zn). Before the trial, soil K (0.10 cmol kg−1) and Mg (0.20 cmol kg−1) contents were suitable, but available P-Bray I (4.2 mg kg−1) was found to be deficient. In course of the study, K, Mg and P deficiencies were observed. An antagonistic effect was observed between rice GY and grain concentrations in P, Mg and Ca for treatments Fc – Mg, Fc – P and Fc – K, respectively. Therefore, the use of P, K and Mg fertilizers is recommended for successive cropping seasons in order to rich stable and high rice yield while decreasing of grain concentrations in P, Mg and Ca can be observed.

Bentyia (Kukyia): a Songhay–Mande meeting point, and a “missing link” in the archaeology of the West African diasporas of traders, warriors, praise-singers, and clerics

The present tragedy in Mali draws our attention to the divisions, tensions and conflicts between West African ethnic groups, religious persuasions, and populations from different regions, in both the present and the past. But a long-term critical perspective on the past brings to light borrowings between cultures, and shows how the mobility of people across West Africa links regional and ethnic histories. The communication axis running from the Aḍagh to the Niger and, along the Niger Valley, from Gao to Busa (in Nigerian Borgu) and beyond, is a strategic locus for investigating this mobility and connectivity. It has linked together the Saharan, savannah, and forest zones of West Africa. It was a magnet for diasporas of Soninke praise-singers and Mande warriors and traders. Fishermen and other waterfolk along the river, oral traditionists and other craftspeople, priests and priestesses of African cults, and Islamic clerics, as well as armies, long-distance merchants, and enslaved human beings, moved along it. Although the archeological sites at Bentyia/Kukyia occupy a strategic position on this historical axis, they have not been excavated, whence a serious gap in our knowledge of the history of the eastern Niger Valley and of West Africa as a whole.

Large-scale pattern of genetic differentiation within African rainforest trees: insights on the roles of ecological gradients and past climate changes on the evolution of Erythrophleum spp (Fabaceae)

BackgroundThe evolutionary events that have shaped biodiversity patterns in the African rainforests are still poorly documented. Past forest fragmentation and ecological gradients have been advocated as important drivers of genetic differentiation but their respective roles remain unclear. Using nuclear microsatellites (nSSRs) and chloroplast non-coding sequences (pDNA), we characterised the spatial genetic structure of Erythrophleum (Fabaceae) forest trees in West and Central Africa (Guinea Region, GR). This widespread genus displays a wide ecological amplitude and taxonomists recognize two forest tree species, E. ivorense and E. suaveolens, which are difficult to distinguish in the field and often confused.ResultsBayesian-clustering applied on nSSRs of a blind sample of 648 specimens identified three major gene pools showing no or very limited introgression. They present parapatric distributions correlated to rainfall gradients and forest types. One gene pool is restricted to coastal evergreen forests and corresponds to E. ivorense; a second one is found in gallery forests from the dry forest zone of West Africa and North-West Cameroon and corresponds to West-African E. suaveolens; the third gene pool occurs in semi-evergreen forests and corresponds to Central African E. suaveolens. These gene pools have mostly unique pDNA haplotypes but they do not form reciprocally monophyletic clades. Nevertheless, pDNA molecular dating indicates that the divergence between E. ivorense and Central African E. suaveolens predates the Pleistocene. Further Bayesian-clustering applied within each major gene pool identified diffuse genetic discontinuities (minor gene pools displaying substantial introgression) at a latitude between 0 and 2°N in Central Africa for both species, and at a longitude between 5° and 8°E for E. ivorense. Moreover, we detected evidence of past population declines which are consistent with historical habitat fragmentation induced by Pleistocene climate changes.ConclusionsOverall, deep genetic differentiation (major gene pools) follows ecological gradients that may be at the origin of speciation, while diffuse differentiation (minor gene pools) are tentatively interpreted as the signature of past forest fragmentation induced by past climate changes.

Taxonomy of the African giant pouched rats (Nesomyidae: Cricetomys): molecular and craniometric evidence support an unexpected high species diversity

Our study combined a mitochondrial cytochrome b phylogeny with cranial measurements from giant pouched rats collected across sub-Saharan Africa. The mitochondrial phylogeny resolves two West African clades and a clade with east and central Africa representatives. This last clade can be further divided into four subclades. Altogether they represent six species (Cricetomys gambianus, Cricetomys ansorgei, Cricetomys emini, and three undescribed taxa) that can be distinguished on the basis of their mitochondrial DNA sequences and craniometry. In the absence of adequate craniometric data the existence of Cricetomys kivuensis cannot be confirmed by our data. Our combined molecular and craniometric data allowed us to broadly delineate the distribution ranges of the detected species. Cricetomys gambianus occurs in the savannah and forest clearings of West Africa. Cricetomys ansorgei is distributed in the savannah of East and southern Africa. Cricetomys emini, as currently recognized across the Guineo-Congolian forest of Africa, is shown to be diphyletic. Cricetomys sp. 1, a separate operational taxonomic unit closely resembling C. emini, occurs in the forest zone of West Africa. An undescribed sister-species of C. ansorgei, Cricetomys sp. 2, occurs in the forest of Central Africa along the left bank of the Congo River. Cricetomys sp. 3 occurs on the right bank of the Congo River from Cameroon to the Republic of Congo, whereas the true C. emini also occurs on the right bank of the Congo River but appears to be restricted to the Democratic Republic of Congo. Cranial phenotype within the genus tends to conform to ecological zonation (either forest or savannah) rather than to phylogenetic affiliation of the species concerned, suggesting that diversifying selection across environmental gradients could be responsible for biological diversification within the genus.

English

The over exploitation of African mahogany in tropical forest has threatened the genetic base of this useful timber and medicinal tree species and as such, an experiment was conducted on the&nbsp;in vitro&nbsp;culture of&nbsp;Khaya grandifoliola, an endangered tree species commonly found in the high forest zones of West Africa to explore its potential for micropropagation. Embryos excised from matured seeds were cultured on Murashige and Skoog (MS) medium supplemented with naphthalene acetic acid (NAA), benzyl amino purine (BAP) and kinetine (KIN) at different concentrations. The optimum result in relation to shoot length, root length, number of nodes and number of root was obtained on MS medium supplemented with 1.0 mg/L BAP + 0.01 mg/L NAA. &nbsp; Key words:&nbsp;Khaya grandifoliola, African mahogany,&nbsp;in vitro&nbsp;culture, medium, embryo, plantlets.

Cover crops for cogongrass (Imperata cylindrica) management and effects on subsequent corn yield

Abstract Cogongrass is widespread in the moist savanna and forest zones of West Africa, where recurrent fires, tillage, weeding, and other farm activities continuously disturb land. Field experiments were conducted in the forest–savanna transition zone of Nigeria from 1996 to 2000 to evaluate the potential of two cover crops (velvetbean and tropical kudzu) for reclaiming land that had been abandoned to cogongrass. Cover crops were grown on the same plots for 3 consecutive yr (1996 to 1998). The control was natural fallow dominated by cogongrass in 1996 to 1998. Corn was planted in all treatments in 1999 and 2000. Total dry matter of cogongrass before the treatments were imposed was 9,000 kg ha−1, and rhizomes contributed 49% of this. At all subsequent sampling dates, plots with cover crops had lower cogongrass shoot and rhizome dry matter than plots without cover crops. Shoot dry matter was reduced to zero 65 wk after planting in both cover crops; rhizome dry matter was reduced to zero after 97 wk in velv...

Termite diversity across an anthropogenic disturbance gradient in the humid forest zone of West Africa

Data are presented for termite assemblages across an anthropogenic disturbance gradient in the humid forest zone of West and Central Africa. Sampling was by standardised 100 m×2 m transects in: primary forest, several ages of regenerating forest, agroforestry plots, short fallows, mixed food crop fields, and mechanically cleared plots. Most sites were in southern Cameroon—two additional transects were conducted in primary forest in Congo (Brazzaville). Species richness was negatively correlated with the disturbance gradient, although transects in areas with a complete or near-complete canopy were broadly similar in species richness. The strongest negative correlation was found for termite species feeding furthest down the humification gradient (group IV soil feeders) probably because these species are energetically constrained from living in non-forest habitats. In contrast species feeding and nesting in dead wood (group I wood feeders) termites, which live in the most protected micro-habitats, were significantly positively correlated with the disturbance gradient. Species composition was also strongly correlated with disturbance level in multivariate redundancy analyses. Pest species were an insignificant element of the assemblage, in part because of the distance of the sites from savanna source pools. Overall, it appears that termite-mediated wood and litter decomposition may be relatively unaffected by light to moderate disturbance intensity, but that soil-conditioning by termites might be greatly reduced in agricultural land cleared from tropical forest.

Natural and Cultural Spatial Patterning in the Late Holocene Deposits of Shum Laka Rock Shelter, Cameroon

Rock shelters, often containing thick accumulations of cultural debris from repeated occupation, are the most informative archaeological sites in the forest zone of west Africa. They are, however, frequently disturbed by human and natural processes. Extensive excavations at Shum Laka rock shelter yielded a long cultural sequence for the Grassfields in NW Cameroon. The topmost, Late Holocene deposits, are analyzed for natural and cultural spatial patterning through a combination of geomorphic analysis, exhaustive 14C dating, and analysis of spatial distribution of lithic artifacts and pottery refits. we identified post-depositional disturbances and reconstructed for the first time a reliable cultural sequence for the Grassfields during the Late Holocene. Finally, we discuss the transition from the Late Stone Age to the Iron Age in the area along the Gulf of Guinea.

Phosphorus, calcium, and magnesium fertilization effects on upland rice in an ultisol

Acid‐related soil infertility is the major constraint to crop production on low‐activity clay soils in the tropics. We investigated the role of phosphorus (P), calcium (Ca), and magnesium (Mg) in alleviating the acid‐related fertility problem in upland rice on an Ultisol in the humid forest zone of West Africa. A field experiment was conducted in 1994 under rainfed condition to determine the response of an acid‐tolerant, upland rice cultivar (WAB 56–50) to the application of P, Ca, and Mg nutrient combinations. Phosphorus alone or in combination with Ca and Mg significantly increased yield and agronomic and physiological P efficiencies and improved harvest index of the crop. Application of Ca and Mg alone or together had a non‐significant effect on yield, elemental composition of plant tissue at tillering, and the uptake of macro‐ and micronutrients at harvest. The results indicate that P deficiency was the most important nutrient disorder in the Ultisol and that the application of Ca and Mg as plant nutrients was initially not as important to the growth, yield, and plant nutrient status of an acid‐tolerant upland rice cultivar.

Rice yield and productivity gaps in irrigated systems of the forest zone of Côte d'Ivoire

Much of the rapidly growing demand for rice in West Africa will be met from increased production in irrigated lowlands, which cover about 12% of the regional rice-growing area. A large potential for expansion of irrigated areas exists particularly in the inland valleys of the humid forest zone. Current production is characterized by large variability in productivity, management practices and production constraints. Quantifying the variability in rice yield and identifying the determining factors are prerequisites to the development of site-specific recommendations and to improved targeting of technologies. Diagnostic on-farm trials were conducted on 64 irrigated lowland fields in the humid forest zone of southern Côte d'Ivoire, in 1995–1996. This was a part of the regional gradient study of irrigated systems from the desert margin to the humid forest zone. Cropping calendars, field operations and input use were monitored. Weed biomass, rice N uptake, and grain yield were determined in farmers' fields as well as in super-imposed, researcher-managed subplots (clean weeding, no N control, and mineral fertilizer N application). Rice yield potential was simulated by using the Oryza-S crop growth model. Yield losses were attributed to management factors based on performance of rice in researcher-managed subplots (management-related yield gap) and by multiple regression with management options. Grain yields varied between 0.2 and 7.3 Mg ha −1 with mean yields of 3.2 in partially and 4.2 Mg ha −1 in fully irrigated systems, 44% and 57% of the potential yield of 7.3 Mg ha −1, respectively. Age of seedlings at transplanting, timeliness of operations and application of P fertilizer were correlated to yield and explained 60% of the observed variability. Grain yield was correlated with N uptake ( r 2 = 0.93 ***) but not with N application rate. Split application of mineral fertilizer N was associated with a 0.48 Mg ha −1 yield increase ( p = 0.002), regardless of the quantity applied. Additional weeding increased yield only in systems with imperfect irrigation. Weed biomass was reduced with improved water control and it increased with age of seedlings at transplanting, and was higher in direct-seeded than in transplanted rice. Echinochloa spp. were the most common weeds in fully irrigated systems and Panicum laxum was more common in the imperfectly irrigated fields. While improved water management was associated with substantial rice yield increases (1.16 Mg ha −1), the timeliness of transplanting, weeding and N fertilization appears to be the key to increased rice yields in the forest zone of West Africa.