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The Soils of the Lower Eastern Slopes of the Cameroon Mountain and Their Suitability for Various Perennial Crops
Abstract
On the eastern slopes of the Cameroon Mountains soils occurring below the 100- metre contour were surveyed on a scale 1:25,000. Most soils are young marine clay soils used for growing bananas, oilpalms, cocoa, rubber and tea. At some places there are lava streams from the mountains.A more general soil survey was made of the younger and older volcanic soils above the 100-metre contour line and a map, scale 1 : 100,000, was produced.The relative age of the various volcanic deposits could be estimated after completing the study of the origin, genesis and distribution of marine soils, that cover volcanic deposits in the lower part of the plain.The discovery of beach walls at different levels formed as a result of differences in sea-levels and gradual rise of the land, helped to solve various soil problems. Most soils are K-deficient, especially young volcanic soils.
... The cones extend from the elevated summit of MC to the lower foothills in both the NE and SW direction (Suh et al., 2003;Bonne, 2006;Bonne et al., 2008). This corresponds to material of the third volcanic phase defined by Hasselo (1961). This corresponds to initial MC lava flow deposited over Miocene (10 -20 Ma) sediment (Dumort, 1968). ...
... These ridges are made up of weathered volcanic flows thought to correspond to an early stage of growth of the active volcano during the Palaeogene and Pliocene (10 -60 Ma) over Cretaceous soft sediments. They constitute material of the first volcanic phase according to Hasselo (1961). ...
... These two areas have been described as the "young" and "old" volcanic landscape of Tertiary and Quaternary age by Hasselo (1961). The ridges and low elevation cones are covered by several meters thick of soils formed from prolonged and protracted intense weathering. ...
... The cones extend from the elevated summit of MC to the lower foothills in both the NE and SW direction (Suh et al., 2003;Bonne, 2006;Bonne et al., 2008). This corresponds to material of the third volcanic phase defined by Hasselo (1961). This corresponds to initial MC lava flow deposited over Miocene (10 -20 Ma) sediment (Dumort, 1968). ...
... These ridges are made up of weathered volcanic flows thought to correspond to an early stage of growth of the active volcano during the Palaeogene and Pliocene (10 -60 Ma) over Cretaceous soft sediments. They constitute material of the first volcanic phase according to Hasselo (1961). ...
... These two areas have been described as the "young" and "old" volcanic landscape of Tertiary and Quaternary age by Hasselo (1961). The ridges and low elevation cones are covered by several meters thick of soils formed from prolonged and protracted intense weathering. ...
Landslides are well known processes that hamper sustainable development efforts, particularly in developing countries where extreme poverty is already a household to societal scale problem. Though a worldwide issue, landslides remain enigmatic especially with regards to their geometry, causative factors, triggering mechanisms, relationship between triggering factors and landslide occurrence, and the susceptibility of any area to mass wasting phenomena. This thesis presents an inventory and thorough analysis of small–scale devastating landslides that occurred in recent years around the city of Limbe at the base of Mt Cameroon.
A multidisciplinary approach was adopted in order to understand the complex and multi-phase nature of landslide processes. This involved integrating results of traditional field mapping, rainfall measurements, analyses of geotechnical properties, soil mineralogy and geochemistry to get an idea of the processes and mechanisms involved in landslide initiation and mobilisation. From these results, two conceptual models are proposed to explain the occurrence of landslides affecting areas populated by vulnerable people. The thesis thus provides first-hand field-measured geometric characteristics of landslide scars and systematically documents and quantifies for the first time the overall features of volume-limited devastating slides around Limbe. Hence, it provides constraints for modelling, monitoring and remediation efforts that might be applied in other areas affected by similar small-scale failures.
Field observations, geotechnical and mineralogical characterisation suggests that slope failure within the study area is enhanced by human intervention through anarchical construction and slope undercutting whereas natural slope failure is generated as a result of fracture enhanced permeability. This implies that in the absence of external factors the slopes within the study area would generally remain stable for long periods. It also demonstrates that understanding landslide triggering processes and relationships between triggers and slide occurrence could be improved through more accurate recording of landslide events and the corresponding triggering process (intensity, magnitude and duration). This knowlegde can be used in landslide susceptibility assessment which was one of the most significant achievements of this thesis, and in the development of early-warning systems that might enable a reduction in the number of casualties and economic loss from future landslide phenomena.
The findings from the present study have generic value and can be used to tackle small-scale slope instability problems elsewhere in the subtropics.
... Soils within the study area are mottled, reddish brown, yellowish brown and/or pale yellow clayey silt, silt and clays with diverse physical and chemical properties and are described in more detail elsewhere (Che et al., in preparation). Due to limited spatial coverage of the soils analysed during this research project, the soil map produced by Hasselo (1961) was digitised and used in this study (Fig. 3b). According to Hasselo's classification, seven soil types are recognized in the study area: old volcanic soil, ash soil, lava soil, lithosol, valley clay soil, stony soil and fragipan. ...
... The distribution of the soil groups are presented in Fig. 3b. The accuracy of the soil map produced by Hasselo (1961) is not constrained but is expected to be similar to the one of the lithological map. ...
... Modifications include the location of pyroclastic material around Mutengene and a change in the boundary of the lahar deposit; b. Soil map of the Limbe area adapted fromHasselo (1961); c. Land cover map of Limbe and its environs, manually digitised from a supervised classification of a Landsat ETM + image acquired on December 10, 2000; d. ...
The dissected volcanic terrains around Limbe, SW Cameroon are frequently affected by small scale but destructive landslides. In this study, a raster-based data driven method involving seed cells is used to build a landslide susceptibility model for the Limbe area. Factors considered to be potential controls of slope failure within this area include slope gradient, rock type, distance from roads, slope orientation, mean annual precipitation, soil type, land cover type, stream density and distance from stream. 63 small to very small translational and rotational landslide scars were identified through extensive field work. Landslide data is randomly divided into a training (75%) and validation set (25%) and seed cells are generated by creating 25 m buffer zones around the head scarp of each scar. The quantitative relationship between landslide seed cells and the above-mentioned factors is established by a data driven approach to obtain weighted factor classes. Summing weighted factor layers, a continuous scale of susceptibility indices is obtained and reclassified into 5 susceptibility classes. Seed cells obtained from the validation data set were used to evaluate the quality of several models involving different controlling factors. Our preferred model combines the weight of 6 factors (i.e. slope gradient, land cover, mean annual precipitation, stream density, proximity to roads and slope orientation). 78% of the validation seed cells are located within the high to very high susceptibility class, which occupy 16.9% of the study area. The obtained susceptibility map is combined with the outline of urban areas and key infrastructures to evaluate zones that are vulnerable to the impact of future slope failures. Such an approach will assist civil protection and urban planning efforts in SW Cameroon.
... The northeast flank and parts of the southeast flank have no slope, which is consistent with the hazard estimation approaching zero at this place ( figure 10(b)). The validity of the approach was also partially tested using existing physiographic maps (Hasselo 1961) indirectly showing the extent of lava flows on the southeast lower slopes of MC. The area referred to as 'soils on lava' (Hasselo 1961) ( figure 10(b)) matches the outline of the hazardous area to the south of MC and on the Buea side where lava flows reach only very rarely, so that 'soils on lava' are much less extensive there. ...
... The validity of the approach was also partially tested using existing physiographic maps (Hasselo 1961) indirectly showing the extent of lava flows on the southeast lower slopes of MC. The area referred to as 'soils on lava' (Hasselo 1961) ( figure 10(b)) matches the outline of the hazardous area to the south of MC and on the Buea side where lava flows reach only very rarely, so that 'soils on lava' are much less extensive there. ...
... (b) Low hazard values along this limit (dashed line) illustrate the consistency of the LAZSLO approach. Results from field investigations (Hasselo 1961, Van Ranst et al. 1989) on the southeast flank of MC show where soils are developed on lava flows (striped areas). The area is extensive where hazard, evaluated using the LAZSLO approach, is relatively high (i.e. ...
Mount Cameroon (MC), West Africa's most active volcano, is a typical example of a hazardous volcano in a densely populated area, often inflicting damage by lava flows. The spatial variation of the lava flow hazard has not been mapped systematically at MC and at many other volcanoes in developing countries because they are insufficiently documented and not continuously, systematically monitored with integrated state‐of‐the‐art methods. Sophisticated lava flow models requiring the specification of numerous physical properties cannot yet be applied in such cases. Hence, a low‐cost approach is proposed to assess the medium‐ to long‐term spatial variation of lava flow hazard. The ‘lava flow zonation system using low‐cost methods’ (LAZSLO) approach takes advantage of freely available topographic data and moderate‐resolution (10–100 m) satellite imagery. For any eruption, the formulation used here expresses the probability of lava flow invasion at any location as a product of the spatial variation of eruption probability and exposure of low‐lying terrain to lava flow reach. The last term is derived by determining the upslope area from where lava flows can invade a given site. A standard UNESCO formula is then used to estimate the lava flow risk. Hazard assessment results at MC indicate that the southwest and northeast flanks are the most hazardous from lava flows, whereas the risk of damage is greatest in the area between Limbe, Mapanja and Batoke, where industrial, urban and tourism infrastructures are developing rapidly. The presented approach can be applied to assist local authorities with disaster preparedness and emergency planning at many poorly studied volcanoes, particularly in developing countries with limited financial resources.
... Payton [37] describes the soils around Mount Cameroon as being varieties of Andosols, derived from alkaline basaltic material. Hasselo [36] identified volcanic and alluvial as the two sources of the parent material of the soils. The volcanic soils are said to be either products of the weathering of basement rocks (lava flows), the direct deposition of aeolian volcanic ash, the deposition of mudflows (comprising of volcanic ash and other loose material in valleys and low-lying plains) washed down from the slopes, or a combination of these. ...
... The volcanic soils are said to be either products of the weathering of basement rocks (lava flows), the direct deposition of aeolian volcanic ash, the deposition of mudflows (comprising of volcanic ash and other loose material in valleys and low-lying plains) washed down from the slopes, or a combination of these. Patches of al-luvial soils considered to be of marine origin and believed to have been deposited at high sea levels are also reported in the low lying land below the 100 m contour line [36]. The soil colour reflects the age, degree of laterization and organic matter content. ...
... Thus, there is an urgent need to increase oil palm yields in Cameroon in order to satisfy the increasing demand. Tiko plain, the Mungo area and the Mpundu-Meanja area) were evaluated for various perennial crops including the oil palm [7]. In this evaluation, emphasis was laid on the boundaries between different landscapes and soil types, notably volcanic and non-volcanic soils [7]-however, it has been reported that the seemingly uniform soil patterns observed in the Tiko plain show great variability in soil types and properties [8]. ...
... Tiko plain, the Mungo area and the Mpundu-Meanja area) were evaluated for various perennial crops including the oil palm [7]. In this evaluation, emphasis was laid on the boundaries between different landscapes and soil types, notably volcanic and non-volcanic soils [7]-however, it has been reported that the seemingly uniform soil patterns observed in the Tiko plain show great variability in soil types and properties [8]. Another land suitability evaluation was conducted for oil palm cultivation in the Boa plain (West and Northwest of Mount Cameroon) and it was reported that the soils were in general fertile and suitable for the cultivation of oil palm but it was also noticed that some areas within the plain were susceptible to flooding and thus necessitated some specific management considerations [9]. ...
Declining yields in oil palm fresh fruit bunch (FFB) have been recorded over the past years in the coastal lowlands of southwest Cameroon and current actual yields are very low (< 12 t FFB ha-1yr-1) compared to the potential yields (25 t FFB ha-1yr-1). One of the problems limiting optimum oil palm production is lack of detailed pedological information to guide plantation establishment and management. A land suitability evaluation was carried out for some major oil palm producing areas of southwest Cameroon to identify land qualities limiting optimal production. Thirteen sites (9 with sedimentary parent materials and 4 with volcanic parent material) were evaluated using a parametric method. Results indicate that climate was not a major limiting factor for oil palm production in coastal plains of southwest Cameroon. However, soil physical characteristics (mainly clayey texture and poor drainage) and soil fertility constitute limitations to oil palm production. Specifically, limitations in cation exchange capacity (CEC), base saturation (BS), organic carbon (OC) and pH were slight to moderate while K mole fraction was the most severe and the most limiting in all the sites. The fertility limitations were more pronounced in soils derived from sedimentary parent materials where 33% had limitations caused by soil pH and OC compared to none for volcanic soils. In addition, 77.8% of sedimentary soils had limitations caused by CEC compared to 25% for volcanic soils. Considering the overall suitability, soils derived from volcanic parent materials were potentially more suitable for oil palm cultivation ((S3) - 50%, (S2) - 50%) compared to sedimentary soils ((N) – 11%, (S3) – 78% and (S2) – 11%). Based on the suitability classes of the different soils derived from dissimilar parent materials, appropriate site-specific soil management is needed to improve oil palm yields, especially with emphasis on K fertilization and improved soil water management. Plantation management in coastal plains of South West Cameroon therefore should factor in differences in soil parent material.
... According to Dumort (1968) these were laid down during the Tcrtiary (Mio-Pliocene), thus having about the same age as the early eruptiva in the Mount Cameroon area. When looking in detail Tiko plain consists of a scrics of fluvio-marine terraces at successive lower levels (Hasselo 1961) and at least part of the sediments are thought to have a younger, Quaternary age. The Mondoni area for instance (figure 1) should be regarded as a subrecent alluvial basin with deposits showing fresh stratification of sands and clays (Kips and others 1984). ...
... Lithologically Tiko plain cari be divided into two parts (Hasselo 1961): the so-called volcanic part with finely layered tuffites in the SW and the non-volcanic part in the NE (Fig.1). In this pnper we concentrate on the non-volcanic part, which consists of unconsolidated sediments with fair amounts of quartz in the Sand and silt fractions. ...
... Mount Cameroon or Fako in local dialect, which is still vo1canically active and situated at the southem end of the vo1canic range in West Cameroon, culminates at 4,095 m a.s.l. This vo1cano shield covers an area of some 1,600 km 2 , in which the so-called 'old' and 'young' vo1canic landscapes, of Tertiary and Quatemary age, respectively, can he distinguished (Hasselo, 1961). ...
E. VAN RANST E.T.AWAH I. HOF The lower southeastern slopes of Mount Cameroon show an intricate geomorphological pattern, in which different physiographic units can he distinguished. The soils derived from the Quaternary basaltic materials are interesting for several reasons : cartography, classification, soil genesis and land use. The close relationship between soil type and geomorphology implies that landscape features can be used to delimit map units in which the variability of morphological and physico-chemical properties is almost negligible.
... At higher elevations, these soils change rapidly to very young, shallow coarse-textured andosols containing very little water, interspersed with extensive areas of bare recent lava flows and cinder deposits. It has been suggested that recent volcanic activity and immature droughty soils are the major factors limiting tree growth at higher elevation (Hasselo, 1961;Payton, 1993). Restriction of species distribution to one or two elevation categories might be simply because dispersal has only just begun and they have not had enough time to expand their range into other habitats. ...
This work was carried out on Mount Cameroon, South West Region of Cameroon. It focused on producing an inventory and distribution of Annonaceae along the elevation gradient on the mountain. As a matter of fact, how Annonaceae flora change along an elevation gradient has never been studied for Mount Cameroon. The Complete Census Method was used. Twelve sites, located at three elevation categories: low (lowland: sea level to 700 m), mid (submontane: 800 to 1800 m), and high (montane: 2200 to 3500 m) were investigated. At each site, 8 transects of 500 m × 10 m were sampled and all the Annonaceae species enumerated. To supplement the information gathered on measured plots and to generate a complete list of target species, plotless sample method was used. This entailed the collection of materials along footpaths and within particular habitats such as ravines, seasonal streams, and disturbed areas. A total of 49 species in 21 genera including climbers, shrubs and trees were collected and identified from both plot and plotless samples. Low and mid elevations were rich in Annonaceae with 37 species in 17 genera and 31 species in 16 genera, respectively. The family was nearly absent from high elevation with only one species. Sixteen species in 10 genera were restricted to low elevation and 11 species in 8 genera confined to the mid elevation. Only Uvariodendron connivens was abundantly found at both low and mid elevations. Three species were frequent and confined to low elevation only. One and five species appeared occasionally and were restricted to low and mid elevations, respectively. 23, 18 and 1 species were rare at low, mid and high elevations respectively. Low elevation showed a higher species diversity (H' = 2.65) than the mid elevation (H' = 0.48). The high elevation with two individuals in a single species was the least diverse (H' = 0.15). The species were more even in their abundance distribution within the low elevation (J = 0.76) than in the mid elevation (J = 0.15).
... Radiometric dates from a dyke and from cores around Mt Cameroon suggest that the oldest rocks in this area are about 4.7-9 Ma (Hedberg, 1968;Marzoli et al., 2000) or 10 Ma (Fitton et al., 1983). • E-W trending, deeply dissected and eroded volcanic massif that predates the growth of Mt Cameroon generally referred to as the Limbe-Mabeta Massif (Géze, 1943;Hasselo, 1961;Hedberg, 1968). ...
This study analyses the behaviour and mobility of major and some trace elements during the physical and chemical development of landslide-prone soil profiles in Limbe, SW Cameroon. The soils result from in situ weathering of Tertiary basaltic and picrobasaltic rocks. Textural and chemical characterisations, together with two mass balance models are applied to understand the mobility and redistribution of elements during the weathering of pyroclastic cones and lava flows. Weathering indices are used to estimate the extent of weathering. The chemical composition of the samples is evaluated by Inductively Coupled Plasma – Optical Emission Spectroscopy (ICP-OES) and their mineralogical composition by X-Ray Diffraction (XRD) analyses. It is observed that intensive weathering results in thick meta-stable soils in which significant loss of Ca, K, Mg, Na and Sr has taken place. There is a noticeable relative enrichment in all analyzed trace elements (Ba, Zr, Y, Sc, V, Ni, Co). Ti, Fe, Al, Mn, Ti, P and Ce tend to be leached in some horizons and concentrated in others. Zr, Ti, and Ce concentrations are greater in the soils than in the bedrock but show slight fluctuations in the soil and saprolites hence cannot be used as immobile elements for mass balance evaluations. Y increases progressively with advanced weathering. Major secondary mineral phases developed through weathering are a mixture of expanding (smectites) and non-expanding clays (kaolinite, halloysite and mica). The profiles show the presence of textural heterogeneities that can be exploited as slip surfaces. Data ploted in Si-Al-Fe diagram point out that the most advanced stage of weathering noted in these profiles is the kaolinisation stage.
... Radiometric dates from a dyke and from cores around Mt Cameroon suggest that the oldest rocks in this area are about 4.7–9 Ma (Hedberg, 1968; Marzoli et al., 2000) or 10 Ma (Fitton et al., 1983). @BULLET E–W trending, deeply dissected and eroded volcanic massif that predates the growth of Mt Cameroon generally referred to as the Limbe–Mabeta Massif (Géze, 1943; Hasselo, 1961; Hedberg, 1968). Rocks within the study area either lie exposed at the surface or are mantled by several metres thick of dark brown, reddish brown and/or pale yellowish sticky, clayey soils derived from protracted intense or deep weathering. ...
Limbe town and surrounding areas, on the SE foot slopes of the active Mt Cameroon Volcano, have experienced numerous small-scale
shallow landslides within the last 20years. These resulted in the loss of ~30 lives and significant damage to farmland and
properties. Landslides and their scars are identified in the field, and their geometry systematically measured to construct
a landslide inventory map for the study area. Specific landslides are investigated in detail to identify site-specific controlling
and triggering factors. This is to constrain key input parameters and their variability for subsequent susceptibility and
risk modeling, for immediate local and regional applications in land-use planning. It will also enable a rapid exploration
of remediation strategies that are currently lacking in the SW and NW regions of Cameroon. Typical slides within the study
area are small-scale, shallow, translational earth, and debris slides though some rotational earth slides were also documented.
The depletion zones have mean widths of 22m±16.7m and lengths of 25±23 standard deviation. Estimated aerial extents
of landslide scars and volume of generated debris range from 101 to 104m2 and 2 to 5×104m3, respectively. A key finding is that most slope instabilities within the study area are associated with and appear to be
exacerbated by man-made factors such as excavation, anarchical construction, and deforestation of steep slopes. High intensity
rainfall notably during localized storms is the principal triggering factor identified so far. The findings from this case
study have relevance to understanding some key aspects of locally devastating slope instabilities that commonly occur on intensely
weathered steep terrains across subtropical Africa and in the subtropics worldwide and affecting an ever denser and most vulnerable
population.
KeywordsCameroon–Landslide–Scar geometry–Sliding mechanism–Causal and triggering factors
... The wildlife of the region is rich, with populations of Cercopithicene primates, forest elephant (Loxodonta africana cyclotis) and chimpanzee (Pan troglodytes elliotii) (Gadsby and Jenkins 1992), and at least two endemic birds (Fotso et al. 2001). The soils are of recent origin, on young volcanic rocks and fertile, though with poor water retention capacity (Hasselo 1961;Proctor et al. 2007). The fertile volcanic soils of Mount Cameroon and its hinterland support extensive oil palm (Elaeis guineensis) plantations (Proctor et al. 2007). ...
Changes in permanent sample plots in the lowland, submontane and montane forests on Mount Cameroon (4,095 m above sea level),
an active volcano, are described for 15 years from 1989 to 2004. Throughout the study period, the stocking level of trees
with a diameter at breast height (DBH) ≥ 10 cm in the three forests were lower than in pan-tropical stands suggesting a significant
impact of volcanic and human-related activities on the vegetation communities on the mountain. Annual mortality rates in the
submontane and montane forests were consistent with those reported for comparable altitudinal ranges in the Blue Mountains
of Jamaica. The annual mortality rate was higher in the lowland forest than other lowland sites included. Divergence between
recruitment and mortality rates was large suggesting that the three vegetation communities have not reached their climax.
The seven-year difference in half-life of large trees (with a DBH ≥ 50 cm) in the submontane and montane forests suggests
an altitudinal effect on turnover of larger trees that in turn contributes to the frequent small stature of high altitude
forests. There was little evidence of an altitudinal effect on species turnover and growth rate. This finding supports generalizations
about the zero effect of growth on the stature of high altitude trees. Understanding forest dynamics is crucially important
in the management of tropical montane environments and in this instance particularly so given the recent creation of the Mount
Cameroon National Park.
KeywordsGrowth rates–Recruitment–Mortality–Altitude–Half-life–Mount Cameroon
... Properties of landforms, particularly Mount Cameroon or Fako in local dialect, which is still vo1canically active and situated at the southem end of the vo1canic range in West Cameroon, culminates at 4,095 m a.s.l. This vo1cano shield covers an area of some 1,600 km 2 , in which the so-called 'old' and 'young' vo1canic landscapes, of Tertiary and Quatemary age, respectively, can he distinguished (Hasselo, 1961). ...
A comparison of bulk geochemistry of alluvial terrace sands from three basins differing in basin lithology and/or climate has been made, using factor analysis to study the behaviour of individual element groups, related to specific minerals. In the Allier basin in the French Central Massif underlain by volcanic and basement rocks temporal changes in the composition of the supplied sediment outweigh compositional changes due to weathering. In the Dore basin, in the same region, consisting of basement rocks essentially, weathering outweighs compositional change in Quaternary terraces, but older quartz rich Plio-Pleistocene sediments are still clearly individualized geochemically. In the Caqueta Basin in the Colombian Amazones weathering affected immature terrace sediments of Andean provenance even in low terraces to such an extent that they are difficult to distinguish from quartz rich Tertiary sediments of Amazonian provenance. Parent material effects, therefore, must be taken into consideration when studying chronosequences in fluvial terraces. -Authors
Throughout the world, agricultural zones are determined mainly by their climate and the stage of their economic development. However, an initial survey of farming regions in the tropics can use the climatic factor alone: since in these lower latitudes there are, so far, only developing countries whose economies do not differ greatly.
The concept of Inceptisols is essentially two fold, that is (1) those soils that have undergone some modification of the parent material but not to the extent that diagnostic horizons such as spodic, argillic, or oxic have formed and (2) soils that do not adequately fit into any other soil order. Some have termed Inceptisols as the “garbage can” in Soil Taxonomy as a result of the contrasting soils found in the Inceptisols. It is undoubtedly necessary to have such an order in soil classification schemes, but it is also evident that as more information becomes available, additional orders can justifiably be recognized and concepts developed. For example, current effort is underway to establish a new order termed “Andisols” that encompasses the volcanic-influenced soils (Andepts). Perhaps, additional orders or regrouping need to be developed from certain soils included in Inceptisols; examples may include the “cold soils” or those in the cryic great groups, the “wet soils” (Aquepts) or the Tropepts.
Tiko plain, stretching out at the southeastern foot of the giant Mount Cameroun volcano (West Cameroon), is an example of an old coastal plain with a large variation in soil properties. These differences can be related to the geomorphic setting of the plain as a sequence of three fluvio-marine terraces, and to the origin of its superficial deposits. Based on the lithology, the Tiko plain can be divided into a volcanic part and a non-volcanic part. The non-volcanic soils show a clear evolution in mineralogy and profile development from the lowest to the highest terrace level. The terrace levels cut across the boundary between the non-volcanic and the volcanic part, but no sequence in mineralogy and soil development is found in the volcanic part. The mineralogical composition of the fine sand fraction is the most important indicator regarding the type of parent material (volcanic or non-volcanic). There is an overall relationship between the mineralogical composition and the cation exchange properties of the soils. These properties highlight the overestimation of CEC by classical methods (NH4OAc, NH4Cl and BaCl2-TEA) where artificially high pH and ionic strength conditions are used in the determination.
1. The geology, soils, climate and levels of human interference of the southern part of Cameroons Mountain are briefly described.
2. On the basis of topographical features and changes in the degree of biotic interference, ten vegetational zones are recognized. The vegetation of each of these is briefly described.
3. The floristics of the ten zones are discussed. Above the forest the Compositae and Gramineae are consistently well represented. Within it there is less tendency for any family to predominate but there are many Orchidaceae and (near the foot of the mountain) many Rubiaceae.
4. The affinities of the vegetation are discussed. Common lowland species form an important part of the flora only near the foot of the mountain. Higher up affinities with the vegetation of several distant areas of Africa are stronger. The affinity with the vegetation of Eastern Africa and that of the nearby island of Fernando Po is pronounced at all levels. A strong affinity with the vegetation of an inland highland area in the same part of West Africa seems to occur only in the case of the Bamenda Highlands.
5. The relationships between the zones are considered. The views ofRichards (1963b) seem to be supported except that a distinction between the forest-derived grasslands and the non-forest derived grasslands between them and the “Paramo” zone seems desirable.
6. A more objective approach to inter-zone relationships employing principal component analysis of presence-and-absence data for each zone proved of little value—presumably because of the variation in floristic richness on the mountain.
Between 1990 and 2000 a number of vegetation surveys were undertaken on the Mount Cameroon area using mainly three methods: 0.25 ha sample plots, 20 m wide transects and rapid botanical surveys. A comparison of these methods in terms of data collected, operational characteristics and output relevance, revealed their strengths and weaknesses. The methods vary markedly in their ecological value (0.25 ha sample plots superior), taxonomic scope and rigour (rapid botanical survey superior) and logistic efficiency (transects superior). The combined outcome of all these surveys is discussed and recommendations made on the use of the rapid botanical survey in order to rapidly fill the remaining gaps on plant distribution. /// Durant la période 1990-2000, une série d'inventaires floristiques a été réalisée au Mont Cameroun. Ces inventaires étaient basés principalement sur trois méthodes: utilisation de placettes d'échantillonnage de 0,25 ha, de layons ou transects de 20 m de large et la technique d'inventaires botaniques rapides. Les points forts et les faiblesses des trois méthodes sont révélés par comparaison des types de données collectées, des caractéristiques logistiques et des résultats obtenus. Les méthodes varient nettement quant à leur valeur écologique (technique des placettes de 0,25 ha étant supérieure), leur rigueur et leur dimension taxonomique (technique d'inventaires botaniques rapides supérieure) et leur efficacité dans la réalisation des opérations (technique des transects supérieure). Les résultats combinés de tous ces inventaires sont discutés et des recommandations formulées pour l'utilisation de la méthode d'inventaires botaniques rapides afin de combler rapidement les lacunes dans la connaissance de la distribution des plantes. Traduit par le journal.
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