Rainforest Belt Research Articles

Net precipitation and soil water dynamics in clearings, old secondary and old‐growth forests in the montane rain forest belt of Mount Kilimanjaro, Tanzania

AbstractThe montane rain forest belt on Mt Kilimanjaro forms an important water source for northern Tanzania that is threatened by both logging and fire. The aim of this study was to investigate the consequences of forest fragmentation on various aspects of the water cycle. Soil properties, rainfall, throughfall and soil water suction were analysed for mature forest, secondary forest patches and large clearings. A total of 10 plots located on the south‐western slopes of the mountain between 2100 and 2300 m.a.s.l. were monitored from May 2000 to June 2002. Annual rainfall amounts ranged from 2000 to 2600 mm with high spatial and inter‐annual variability. Rainfall interception ranged from 3 to 9% of incident rainfall in clearings, to a maximum of 32% in forests. In general, soils under mature forest were wettest and showed only minor moisture fluctuations throughout the year. Soils of secondary forest sites were driest and soil water suction exhibited the largest fluctuations. Additionally, the finer texture of soils under mature forest compared to secondary forest sites allowed higher amounts of soil water to be stored for similar soil water suction levels. Ventilation and radiation penetration, which influence the magnitude of interception, evaporation from the forest floor and transpiration, were probably higher in fragmented secondary than in closed mature forests. In clearings, higher throughfall and presumably lower transpiration rates led to moister conditions compared to adjacent secondary forest sites. Thus, soil conditions under mature forest were most suitable for optimum water storage on Mt Kilimanjaro. The transformation of closed mature forest to a mosaic of forests in different stages of regeneration led to increased spatio‐temporal variability in soil moisture. Copyright © 2010 John Wiley & Sons, Ltd.

Silent spring on podrot reduction and yield of benniseed in an ultisols

Benniseed (Sesanum indicum L.) is well known oil-seed crop grown mostly in the Savannah areas of Nigeria, and with little cultivation in the forest south. A two-season experiment was conducted in 2005 and 2006 to determine the influence of plant density and nitrogen application on podrot, oil content and pod weight of benniseed in the rain forest belt of Nigeria. Analysis of variance indicated that only the podrot and oil content were affected by plant population. An increase of 17.6% and 18.8% in oil content was recorded when plant density increased from 160,000 to 250,000 plants/ha recorded lowest podrot 2.02; 2.30 in the first and second seasons while 45 kg/ha, recording the lowest podrot of 2.59 and 2.63 in 2004 and 2005, respectively. 0 kg/ha (control) recorded the highest podrot of 3.14 and 3.46 in 2004 and 2005, respectively. An increase of 16.6% and 17.5% oil content was recorded when the plant population increased from 160,000 to 250,000 plants/ha in the first and second seasons, respectively. Further increase from 111,111 to 160,000 resulted in a further increase of 4.8 and 6.2 in the first and second seasons respectively. Nitrogen fertiliser is highly significant on podrot (P < 0.05), more so, interaction of plant density and nitrogen application were highly significant on pod weight with 250,000 plants/ha and 45kg/ha nitrogen recording the highest pod weight in 2004 and 2005, respectively. Mean values of main effect indicated optimal yield at the highest plant population of 250,000 plants/ha in the first and second seasons. However, yield was highest at the combination of 45 kg/ha and 250,000 plants/ha in all the seasons investigated.

Cesarean delivery in preeclampsia and seasonal variation in a tropical rainforest belt

The pathogenesis of preeclampsia is poorly understood and recent evidence suggests that the incidence varies depending upon the season. This study was carried out to determine whether there is a seasonal variation in the presentation of preeclamptics undergoing cesarean delivery in a tropical rainforest belt. A university teaching hospital. Retrospective. The hospital records of consecutive patients (July 1996-June 2006) with preeclampsia, who underwent cesarean delivery in a tertiary care centre, were reviewed. Data collected included patient demographics, total number of deliveries, number of cesarean deliveries, and number of preeclampsia patients and time of presentation for cesarean section. Approval of the local ethical committee was obtained. The EPI info software program was used for statistical analysis. A total of 6798 deliveries were recorded during the study period resulting in 6485 live births. There were 1579 cesarean deliveries during the period. Of these, 196 patients had toxemia of pregnancy (166 with preeclampsia and 30 with eclampsia). One hundred and forty-one patients (9% of cesarean deliveries) had cesarean delivery during the rainy season and 55 (3.5%) during the dry season (P < 0.05). Amongst preeclampsia patients, 115 presented (7%) during the rainy season and 51 (3.2%) during the dry season (P < 0.05). In the eclampsia group, 26 (1.65% of cesarean sections) presented during the rainy season and four (0.25%) during the dry season (P < 0.05). There was a seasonal variation in the cesarean delivery required for preeclampsia/eclampsia patients. This may help in counseling women on when to plan their pregnancy in order to reduce the morbidity and mortality associated with this apparent seasonal disease.

A Preliminary Checklist of the Ants (Hymenoptera: Formicidae) of Kakamega Forest (Kenya)

A preliminary species checklist of the ants (Hymenoptera: Formicidae) of Kakamega Forest, Western Kenya, is presented. The species list is based on specimens sampled from 1999 until 2009, which are deposited in the ant collection of the Zoological Research Museum Koenig, Bonn, Germany, and the Natural History Museum of Los Angeles County, Los Angeles, United States. The known ant fauna comprises 11 subfamilies with 52 genera and 288 species. This species richness is the second highest reported from the Afrotropical zoogeographical region. The observed ant fauna can be divided into a group of forest habitat species with approximately 180 species and another group, which consists of about 100 species, of open habitat specialists. The greatest part of the ant fauna (204 species or 71%) could be identified to species level but the rest remains unidentifiable or undescribed (84 species or 29%). The preliminary data from the observed ant fauna seems to support the hypothesis that Kakamega Forest is the eastern-most remnant of the former Guineo-Congolian rain forest belt, while the zoogeographical influence from East African Afromontane forests seems to be less significant.

Evolutionary Influence on Human Landscape Preference

Individuals residing in the rainforest belt of Nigeria were shown photographs of five biomes: rain forest, deciduous forest, coniferous forest, savanna, and desert. Subjects overwhelmingly selected savanna scenes as representing the most desirable place to live. These results, coupled with extensive American data, support the hypothesis that humans possess an innate preference for savanna-like settings, which then is modified through experience and enculturation. Findings are discussed in relation to anthropological, biological, and psychological research.

Effects of Nitrogen and phosphorus fertilizer rates on the growth and yield of sesame (&lt;i&gt;Sesamum indicum&lt;/i&gt; L.) in the southeastern rain forest belt of Nigeria

Effects of Nitrogen and phosphorus fertilizer rates on the growth and yield of sesame (&lt;i&gt;Sesamum indicum&lt;/i&gt; L.) in the southeastern rain forest belt of Nigeria

Management of Podrot, Oil Content, and Pod Weight of Benniseed in an Ultisols

Benniseed (Sesanum indicum L) is a well known oilÐseed crop grown mostly in the Savannah areas of Nigeria, and with little cultivation in the forest south. A two-season experiment was conducted in 1997 and 1998 to determine the effect of plant population and nitrogen application on podrot, oil content and pod weight of benniseed in the rain forest belt of Nigerian. Analysis of variance indicated that only the podrot and oil content were affected by plant population. An increase of 15.6% and 16.2% in oil content was recorded when plant population increase from 111,111, to 250,000 plants/ ha recorded list podrot 2.02; 2.30 in 1st and 2nd seasons while 60kg/ha recorded lowest podrot 2.59; 2.63 in 1997 and 1998, respectively. The 0kg/ha (control) recorded highest podrot 3.14; 3.46 in 1997 and 1998, respectively. An increase of 15.6% and 16.2% oil company was recorded when plant population increased from 111,111 to 250,000 plants/ha in the 1st and 2nd seasons, respectively. Further increase from 62,500 to 111,111 resulted to further increase of 4.6 and 5.2 in the 1st and 2nd seasons, respectively. The 9kg is highly significant on podrot (P

Effect of Time of Introducing Sesame and Nitrogen, Phosphorus, Potassium (15:15:15) Fertilizer on Sesame/Soybean Intercropping in the Southeastern Rain Forest Belt of Nigeria

ABSTRACT Field experiments were conducted during the cropping seasons of 2004 and 2005 at Obubra, Nigeria, to ascertain the most suitable time to introduce sesame or soybean and the effect of nitrogen:phosphorus:potassium (N:P:K; 15:15:15) fertilizer on sesame/soybean intercropping. Treatments comprised five times of introduction as follows: sesame + soybean sown same day, sesame sown two weeks before soybean, sesame sown four weeks before soybean, sesame sown two weeks after soybean, and sesame sown four weeks after soybean. Four levels of NPK (15:15:15) fertilizer (0, 50, 100, and 150 kg/ha) were factorially combined with the above treatments and arranged into a randomized complete block design with three replications. The parameters measured were; plant height, number of branches/plant, number of leaves/plant, shoot dry matter/plant, number of capsules/plant, number of seeds/capsule and seed yield. The number of leaves, branches and capsules per plant, shoot dry matter and seed yield of sesame as well as soybean shoot dry matter, number of pods per plant and seed yield increased significantly when either component was sown earlier than the other. Incremental application of NPK fertilizer up to 150 kg/ha significantly increased, on average, sesame seed yield as well as soybean plant height, shoot dry matter and seed yield. The yield advantages associated with sowing soybean four and two weeks before, same day with and two and four weeks after sesame were 0, 25, 44, 72, and 53%, respectively, over sole cropping. The yield advantages accrued to intercropping at 0, 50, 100 and 150 kg/ha NPK fertilizer were 109, 27, 8, and 11%, respectively. Simultaneous or same day sowing produced more satisfactory yields of the component crops relative to other sowing schedules while fertilizer use was enhanced by NPK application at 150 kg/ha.

Species diversity patterns along the forest savanna boundary in Nigeria

PurposeThis study seeks to investigate the influence of human activities on the patterns of species diversities along the forest‐savanna boundary in Oyo state of Nigeria.Design/methodology/approachA transect was placed along the study area from the rainforest belt, through the forest savanna ecotone to the southern fringe of the Guinea savanna vegetation belt. Each study site was identified as forest or savanna or ecotone using the species found within them. Samples from trees with diameter at breast height ≥ 6 cm were collected and the numbers from the different species counted. Species diversity patterns were analysed using the Shannon and Simpson's Index.FindingsAnalysis of patterns of species diversity with the Shannon and Simpson's Index showed a decrease in the species diversity from sites with mature vegetation to the areas of vegetation succession irrespective of whether they contained forest or savanna vegetation. Also, species diversities was greater in the forest vegetation than in the savanna vegetation. The decrease in species diversity and loss in some species is attributable to the effect of landuse and other human interference along the forest savanna ecotone.Originality/valueThe study suggested measures to reduce biodiversity loss in the forest savanna zones of Nigeria.

Sustainable education at a developing‐world field site: developing programmes linked to conservation work in‐country

In a poverty‐stricken developing country such as Madagascar, it is sometimes difficult to promote conservation strategies and actions when they are at seeming odds with the urgent need for agricultural output. We explore the various methods and approaches used to promote more sustainable land use and, consequently, better protection of natural habitats using the case study of Parc Ivoloina and the Betampona Reserve in the eastern rainforest belt of Madagascar. The key factors in this approach are: the targeting of a diverse audience spanning all age ranges and social niches, identification and development of good quality local trainers and, most importantly, a long‐term approach enabling trusting relationships to be built up with local partners and genuine progress to be seen on the ground.

Forecasting hotspots of forest clearing in Kakamega Forest, Western Kenya

Kakamega Forest is the last remaining rainforest in Kenya and the easternmost remnant of the Guinean-Congolian rainforest belt. As such, it is home to a large number of endemic fauna and flora species. Yet the remaining natural forest is under imminent threat of degradation due to a rapidly growing population in its vicinity and a poverty rate far above the national average. The growing demand for forest resources and ecosystem services will continue to exert great pressure on the remaining forest fragments. In this paper, we predict future hotspots of forest clearing of the remaining natural and old-growth secondary forest in Kakamega Forest. We parameterized an artificial neural network model using resilient backpropagation to simulate the likelihood of forest clearing for each location. Input variables into the network included historic information on forest clearings together with variables capturing the status of forest protection, accessibility to roads and markets, as well as topography and forest density. Simulation results were used to predict future clearings based on observed rates of change. Hotspots of forest clearing were derived by assessing the neighborhood density of predicted clearings. Our results indicate that forest clearings occurred across all forest fragments. Hotspots of future forest clearing tended to occur near roads and market centers. Most future hotspots were found in areas with a lower protection status, where some forest use is allowed. But our model also predicted considerable pressure on remaining old-growth forest resources in the strictly protected National Reserve. Our predictions of deforestation hotspots contribute to a better geographic targeting of nature protection activities and forest management investments in Kakamega Forest. Thus, it will hopefully help policy makers and land managers to strike a balance between satisfying the needs of local livelihoods and preserving the unique ecological values of Kakamega Forest for future generations.

Characterization of 21 microsatellite marker loci in the Milne-Edwards’ Sifaka (Propithecus edwardsi)

Milne-Edwards’ Sifaka (Propithecus edwardsi) is a dark furred lemur with white flanks living in the southern region of the eastern rainforest belt of Madagascar. This species is endangered due to habitat destruction primarily from deforestation. Twenty-one polymorphic nuclear microsatellite loci were isolated from a genomic DNA derived from an individual from Ranomafana National Park, Madagascar. Population genetic parameters were estimated on 10 individuals each, from Andringitra National Park and the Vatoharana Forest in Ranomafana National Park.

The biogeographical assignment of a west Kenyan rain forest remnant: further evidence from analysis of its reptile fauna.

Aim The Kakamega Forest, western Kenya, has been biogeographically assigned to both lowland and montane forest biomes, or has even been considered to be unique. Most frequently it has been linked with the Guineo‐Congolian rain forest block. The present paper aims to test six alternative hypotheses of the zoogeographical relationships between this forest remnant and other African forests using reptiles as a model group. Reptiles are relatively slow dispersers, compared with flying organisms (Aves and Odonata) on which former hypotheses have been based, and may thus result in a more conservative biogeographical analysis. Location Kakamega Forest, Kenya, Sub‐Saharan Africa. Methods The reptile diversity of Kakamega Forest was evaluated by field surveys and data from literature resources. Faunal comparisons of Kakamega Forest with 16 other African forests were conducted by the use of the ‘coefficient of biogeographic resemblance’ using the reptile communities as zoogeographic indicators. Parsimony Analysis of Endemism and Neighbour Joining Analysis of Endemism were used to generate relationship trees based on an occurrence matrix with paup*. Results The analysis clearly supports the hypothesis that the Kakamega Forest is the easternmost fragment of the Guineo‐Congolian rain forest belt, and thus more closely related to the forests of that Central–West African complex than to any forest further east, such as the Kenyan coastal forests. Many Kenyan reptile species occur exclusively in the Kakamega Forest and its associated forest fragments. Main conclusions The Kakamega Forest is the only remnant of the Guineo‐Congolian rain forest in the general area. We assume that the low degree of resemblance identified for the Guineo‐Congolian forest and the East African coastal forest reflect the long history of isolation of the two forest types from each other. Kenyan coastal forests may have been historically connected through forest ‘bridges’ of the southern highlands with the Congo forest belt, allowing reptile species to migrate between them. The probability of a second ‘bridge’ located in the region of southern Tanzanian inselbergs is discussed. Although not particularly rich in reptile species, the area should be considered of high national priority for conservation measures.

A phylogeny of the oil bee tribe Ctenoplectrini (Hymenoptera: Anthophila) based on mitochondrial and nuclear data: Evidence for Early Eocene divergence and repeated out-of-Africa dispersal

The bee tribe Ctenoplectrini, with two genera, comprises nine species in tropical Africa and ten in Asia and Australia. Most of them collect floral oil, pollen, and nectar from Cucurbitaceae, but three species are thought to be cleptoparasites. The unusual morphology of Ctenoplectrini has made it difficult to infer their closest relatives, in turn preventing an understanding of these bees’ geographic and temporal origin. We used two mitochondrial and two nuclear markers (4741 nucleotides) generated for most of the species to test the monophyly of the tribe, its relationships to other Apidae, and its biogeographic history. Ctenoplectrini are strongly supported as monophyletic and closest to the Long-horned bees, Eucerini. The presumably cleptoparasitic species form a clade (Ctenoplectrina) that is sister to the remaining species (Ctenoplectra), confirming the independent evolution of cleptoparasitism in this tribe. Tree topology and molecular dating together suggest that Ctenoplectrini originated in Africa in the Early Eocene and that Ctenoplectra dispersed twice from Africa to Asia, sometime in the Late Eocene, 30–40my ago, from where one species reached the Australian continent via Indonesia and New Guinea in the mid-Miocene, c. 13my ago. Dry and cool mid-Miocene climates also coincide with the divergence between Ctenoplectra bequaerti from West Africa and Ctenoplectra terminalis from East and South Africa, perhaps related to fragmentation of the equatorial African rainforest belt.

Assessment of abdominal scarification as a treatment for malaria-induced splenomegaly in a rural community: Implications for child health

This descriptive cross-sectional study was conducted in Ugbegun, a rural community in the rainforest belt of Edo State, Nigeria. The objective of the survey was to determine the prevalence of abdominal scarification and associated factors. There were 640 houses within the community; using a sampling ratio of 1:2, 320 houses were selected by a systematic sampling technique. Within the 320 houses were 425 households. Fifteen of them had no children in the age group 2–9 years. A total of 410 households had children eligible to participate in the study. Twenty (4.9%) of the heads of households declined to participate, while 390 (95.1%) agreed and constituted the study population. The parents' perception of splenomegaly and the use of scarification in its treatment were sought while children within the age range were examined for splenomegaly. Results showed that parents' perception of splenomegaly was poor. Eighty-three per cent claimed that splenomegaly is an enlarged painful abdomen, 80.0% believed that it is a common childhood disease, while 51.0% believed that it is an accumulation of bad blood. Only 24.3% attributed it to malaria. Indicators for abdominal scarification were common signs and symptoms of simple and complicated malaria. Of the 390 children examined, 302 (77.4%) were scarified and of these only 106 (35.1%) had splenomegaly. In conclusion, abdominal scarification is still a common practice in the community, undertaken as treatment for enlarged spleen resulting from malaria. The practice is not beneficial but, on the contrary, compromises the health of the sick child. There is a need for the education of parents in rural communities about simple prevention methods, such as the use of insecticide-treated nets (ITNs), correct identification of early signs and symptoms and the adequate treatment of malaria to reduce complications and eventual death. This can be achieved using the village health worker and health committee.

Determination of benefit of early identification of severe forms of malaria in peripheral centres in South Eastern Nigeria

Background/Aims: A pilot study to determine benefits of early identification of severe forms of malaria in peripheral centres was carried out in 3 rural communities of South Eastern Nigeria. Methodology: The study area is located in the rain forest belt of South Eastern Nigeria with high temperature and humidity. It is a typical rural setting with hardly accessible roads, very little physical infrastructure and difficulty in access to health care facilities. Results: After 4 months of the study, a total of 788 patients were seen in the 3 sites. Patients presenting with malaria symptoms totalled 543 representing (68.9%). The male /female distribution is 297 and 246 respectively. Out of 421 blood smears for malaria parasite done, 192 were positive. Most (335) of the patients with malaria symptoms were children aged less than 4 years. Forty-seven patients presented with severe forms of malaria of which 35 (74.5%) were children under 10 years. All the 47 patients with severe malaria were referred to the usual centre and followed up subsequently. While 2 (4.26%) of them died, the rest 45 (95.74%) survived and were discharged after a mean duration of stay of 6 days. Conclusion: The importance of immediate referral of identified cases was validated by this study. Keywords: benefits, treatment, severe malaria Sahel Medical Journal Vol. 8(4) 2005: 79-82

Variability studies and fruit characteristics of &lt;i&gt;Dacryodes edulis&lt;/i&gt; (G. Don) H.J. Lam) in Southeastern Nigeria

In a survey conducted in Imo, Delta, Enugu, Abia and Rivers States within the rain forest belt of South-eastern Nigeria, fruits of Dacryodes eduli were grouped according to their sizes and fruit colour. The relationshipd between fruit colour and fat, protein, sodium, calcium and potassium contents in fruit pulp were examined. There were no significant differences in chemical composition of the fruit pulp. Midnight blue fruits appeared to have highest quantity of protein and mineral elements while purple coloured fruits had the greatest quantity of fat. The least amounts of protein and fat were contained in pink coloured fruits. However, morphological characteristics such as fruit weight and length varied significantly within and between states. The importance of the morphological and biochemical characteristics is addressed.Keywords: variability, fruit characteristics, Dacryodes edulisInternational Journal of Agriculture and Rural Development Vol. 6 2005: 6-11

Late Quaternary palynology in marine sediments: A synthesis of the understanding of pollen distribution patterns in the NW African setting

After a review of the first steps in marine palynology, we show that the understanding of the northwest African setting is crucial to evaluate the potential of marine palynological studies elsewhere. We studied distribution patterns of pollen grains in recent marine sediments off NW Africa and were able to clearly relate patterns to modern pollen source areas (vegetation belts) and operating transport systems (wind belts and ocean currents). In particular patterns of Quercus, Artemisia, Chenopodiaceae–Amaranthaceae, Ephedra, Gramineae, and wet forest trees are very indicative of the position of the vegetation belts on the adjacent continent. Aeolian pollen transport is carried out by the northeast trade winds and the African Easterly Jet (AEJ). In the rain forest belt transport of pollen and fern spores also occurs by rivers. A detailed comparison between recent pollen rain samples from terrestrial and marine sites between 21 and 12°N showed that the latitudinal range of vegetation belts is clearly reflected in the pollen samples of both environments. A migration of the southern border of the Sahara is reflected by the changing ratio between Chenopodiaceae–Amaranthaceae pollen from the desert and Gramineae pollen from the savannah belt. Distribution patterns of pollen for 9000 and 18,000 14C yr BP (last glacial maximum) time-slices, based on pollen records from eleven marine cores between Portugal and the Gulf of Guinea show significant latitudinal migrations of vegetation belts, but a stable position of the main wind trajectories. The AEJ had a stable position around 21°N. The belt with trade winds had a stable position from Morocco southwards. Changing vigour of the trade winds is clearly reflected by the patterns of isopollen contours and by changes in pollen influx records.

A Holocene vegetational and climatic record from the Atlantic rainforest belt of coastal State of São Paulo, SE Brazil

Holocene vegetation and climate have been reconstructed by means of pollen analysis in a 643-cm-long core from the Jacareı́ peat deposits (23°17′S, 45°58′W, 550 m a.s.l.) within the Atlantic tropical rainforest belt in the State of São Paulo, SE Brazil. Three conventional 14C dates indicate that the onset of peat formation started at 9720 years BP. Due to sampling restrictions, the record encompasses the period between 9720 and ca. 1950 years BP. The palynological content of the samples permitted the recognition of five distinct climatic periods between 9700 and ca. 1950 years BP: humid and cool climate from 9720 to ca. 8240 years BP, humid and warm from ca. 8240 to ca. 3500 years BP, cooler and moister than today from 3500 to 1950 years BP. The return of a cool climate at the late Holocene is suggested by the reappearance of montane and humid forest taxa such as Araucaria, Drimys, Daphnopsis, Ericaceae, Podocarpus and Myrsine in the upper sections of the pollen diagram. Throughout its formation, the Jacarei peatbog has had a very different botanical composition. Gleichenia was the most important taxon in the peat bog from 9720 to 8240 years BP, followed by Selaginella, Polypodium and Asplenium until 5400 years BP. A Sphagnum/ Lycopodium dominated peat was established from 5400 to 3500 years BP, followed by Gleichenia/ Sphagnum from 3500 to ca. 1950 years BP. The interpretation of the pollen and spore diagrams permitted a correlation between the vegetational and climatic signal contained in the Jacareı́ peatbog with other locations in southeastern and southern Brazil.

Late Holocene climatic changes in west Africa, a high resolution diatom record from equatorial Cameroon

Holocene climatic changes in West Africa are usually explained by increased/decreased activity of the monsoon from the Guinean Gulf toward the continent. According to a diatom record from Lake Ossa (3°50′N, 9°36′E), we suggest that, in the near coastal areas of Cameroon, phases of intensification of the monsoon were marked by reduced precipitation and reduced evaporation, conditions nowadays prevailing South of the equator (4–5°S) during the austral winter. Lake Ossa is a shallow lake located in one of the rainiest area of the African rain forest belt. During the wet season (March–November) it is fed by acid meteoric waters entailing low pH in the lacustrine waters. During the dry season (December–February) groundwater discharges allow the persistence of acid waters near the borders of the lake, but, in the inner parts, the waters tend to be alkaline, alkaliphilous diatoms are abundant in the surface sediment samples and are used as indicators of low precipitation. At that time, atmospheric dust containing reworked diatoms from Saharan Quaternary deposits is transported by the northern trade winds and reaches the Ossa area. Wind blown diatoms are considered as a signature of the northern trade winds. A diatom record from the western deep part of Lake Ossa has provided climatic data for the mid-late Holocene at a resolution of 50–60 years. A major climatic change at 2700 cal yr BP was marked by the appearance of wind blown diatoms. A millennial-scale alternation between low and high precipitation episodes is recorded during the last 5500 years. The low precipitation episodes before 2700 cal yr BP are interpreted as a consequence of a northward extension of the climatic conditions that nowadays characterize the Southern Congo during the austral winter, when the monsoon extends into West Africa and reaches the northern sub-tropical latitudes. The effects of low precipitation on the water balance and on the rain forest were obliterated by an extremely low evaporation. Between 2700 and 1300 cal yr BP, precipitation was high and the rain forest intensively disturbed in response to convective storms. A low precipitation episode between 1300 and 600 cal yr BP is explained, contrarily to the previous similar episodes, by tropical rainfalls located farther South than today during a larger part of the year. The modern climate settles at about 600 cal yr BP. The climatic oscillations on a millennial time scale were apparently coincident with temperature changes in the Northern and Southern Atlantic suggesting that the monsoon over West Africa was essentially driven by interactions between both hemispheres. This interpretation is in agreement with available data from other equatorial and sub-tropical regions of West Africa.