Diversity, Distribution, and Abundance of Plants in Lewoh-Lebang in the Lebialem Highlands of Southwestern Cameroon

. A survey was conducted between October 2010 and June 2011 to determine the diversity, distribution, and abundance of plants in 4 sites of the Lebialem highlands and to relate species diversity and abundance to altitude and soil types. Twelve (12) plots, each of 1 ha (250 × 40m), were surveyed at the submontane and montane altitudes of the sites. One hundred (100) species belonging to 82 genera were identified with the genera Cola and Psychotria being the most represented. Vulnerable species included Guarea thompsonii , Schefflera hierniana , Allanblackia gabonensis , Cyclomorpha solmsii , Vepris trifoliolata , and Xylopia africana . Species such as Xymalos monospora , Tricalysia atherura , and Piptostigma oyemense present in the study area were endemic to Cameroon. Diversity and distribution of plants were affected by parameters such as the altitude and the soil type. Soil analysis revealed that diversity in the study area was affected by the organic carbon, nitrogen, calcium, and the cation exchange capacity of the soil.


Introduction
Biodiversity is the degree of variation of life forms within a given ecosystem, biome, or entire planet [ ]. It encompasses all species of plants, animals and microorganisms, the ecosystem, and ecological processes of which they are parts. It is an umbrella term for the degree of nature's variety, including both number and frequency of ecosystems, species, or genes in a given assemblage. Wilson [ ] de nes biodiversity as the variety of organisms considered at all levels from genetic variants belonging to the same species through arrays of species to arrays of genera, families, and still higher taxonomic levels.
Besides South Africa, Cameroon is the most biologically rich country known to date on the African continent [ ]. It encompasses an intricate mosaic of diverse habitats with moisttropicalforestdominatingthesouthandsouth-eastand covering % of the country, mountain forest and savannah in the highlands and sub-Sahelian savannah and near desert in the far north [ ]. ese diverse habitats harbour more than , species of plants, species of which are endemic. e majority of the endemic taxa are concentrated around Mount Cameroon and other highland areas. During the last few decades, deforestation of tropical forests areas has accelerated at an alarming rate as extensive areas of forest are beingclearedeveryyear[ ]. Man a ects the forest ecosystem with activities such as agroindustries, shi ing cultivation, and hunting.
ere has been an overwhelming concern about the loss of tropical diversity and an emphasis on the identi cation of biodiversity hot spots in an attempt to optimize conservation strategies [ ].
Diversity studies carried out in Cameroon have covered many parts of the country but le out certain regions despite their richness in plant diversity [ , ]. An example of such a region is the Lewoh-Lebang area in the Lebialem Division. Lebialem is located in the southwest region of Cameroon, and it is characterized by a hilly topography with a rich diversity of ora and fauna. is mountain ecosystem has been under serious pressure from the local people. e ecosystem is a centre of high endemism for many taxa (plants, amphibians, m a m m a l s ,a n db i r d s ) ,a n di t sd e s t r u c t i o nc o u l dl e a dt ot h e local extinction of globally threatened biodiversity (plants, mammals,, etc.), watershed destruction, and degradation of International Journal of Biodiversity livelihood systems, property, and lives. e region also holds some of the globally threatened and endemic species such as the critically endangered cross river gorilla, chimpanzee, ying squirrel, endangered Bannerman's Turaco and Banded Wattle-eye, vulnerable Red-headed Picathartes [ ]. e study area is part of the Bamboutos Mountain Range which is a stronghold of montane biodiversity. ese ecosystems around the Bamboutos Mountain continue to provide valuable goods and services to local people in the region and areanimportantwatershedlodgingthetributariesofManyu River that drain into the cross river. Due to precedent geologicalandgeographicalhistoryofthesemountainareas and coupled with the high annual rainfall ( to mm) and humidity, these areas are perpetually having landslides [ , ]. Most of the landslides are as a result of anthropogenic activities of the communities around the mountain [ ]. e Nweh people (tribe in the study site) practice slash and burn a g r i c u l t u r ew i t hab i m o d a la n n u a lf a r m i n gc y c l ew h i c hi s entirely dependent on the rain fall patterns that results in frequent landslides [ ]. Information on the type and the distributional patterns of plants may help to put in place proper management schemes on biodiversity conservation.
is work therefore assesses the diversity, distribution and abundance of plants found in Lewoh-Lebang landscape in Cameroon so as to propose management schemes for biodiversity conservation.

Materials and Methods
. . Study Area. Lebialem is located in the northeastern part of the southwest region of Cameroon (latitudes ∘ ὔ Na n d ∘ ὔ N and between longitudes ∘ ὔ Eand ∘ ὔ E) [ , ].
Lewoh-Lebang is located between latitudes ∘ ὔ and ∘ ὔ N and longitudes ∘ ὔ Ea n d ∘ ὔ E and at altitudes ranging from to m ( Figure ). e climate of this region i ss i m i l a rt ot h a to ft h eC a m e r o o nm o u n t a i nr a n g ew h i c h is characterized by high winds and low sunshine [ ]. e average daily temperature varies very much with seasons but hasrangesof to ∘ C, and the mean annual rainfall range from was mm [ ]. e main vegetation type is grassland with patches of montane and submontane forests m a i n l ya sar e s u l to fh u m a na c t i v i t i e sp a r t i c u l a r l yc o c o y a m farming in the lowland forest [ ].
. . Sampling. Sampling was carried out in four di erent sites: Atullah ( ∘ ὔ Na n d ∘ ὔ E), Leleng ( ∘ ὔ Na n d ∘ ὔ E), Mbindia ( ∘ ὔ Na n d ∘ ὔ E), and Nyitebong ( ∘ ὔ Nand ∘ ὔ E). Each site was divided into submontane ( -m altitude) and montane levels (≥ m altitude). e study sites and the altitudes used were subdivided following the classi cation done by Harvey et al. [ ]. Within each of the stratum, a plot of ha ( m × m) was laid and was subdivided into subplots of × m placed at regular intervals of m from each other. Within each plot, all individual trees were identi ed, measured, and recorded. Taxa were identi ed in situ by a taxonomist from the Limbe Botanic Garden. e diameters at breast height of the species were measured using a diameter tape. Trees were grouped into the following diameter classes: small trees ( -. cm), medium-sized trees ( -. cm), and large trees (> . cm) following a grouping done by Kenfack et al. [ ]. ese species were further grouped into four life forms de ned by their maximum attainable heights as follows: treelets (small trees) (< m), understorey ( -m), canopy ( -m), and emergent (> m) [ ].
Voucher specimens were prepared and compared with those at the Limbe Botanic Garden Herbarium (SCA) and the Cameroon National Herbarium (YA). Rare species were identi ed in situ to prevent forward destruction. At each altitude level, soil samples were collected, air dried and standard procedures [ -]w e r eu s e dt oa n a l y s et h es a m p l e s . e following soil parameters were analysed: soil pH determined in the ration of : (w/v) soil water suspension, organic carbon by chromic acid digestion and spectrophotometric analysis [ ]. Total nitrogen was determined by wet acid digestion [ ], and exchangeable cations (calcium, magnesium, and potassium) were extracted using the Mehlichprocedure [ ] and atomic absorption spectrophotometry. Available phosphorus was extracted by the Bray-procedure andanalysedusingthemolybdateblueproceduredescribed by Murphy and Riley [ ].
. . Data Processing and Analysis. Species diversities were determined using the Shannon-Weaver Diversity Index ( ) : =( )(logn ), where = / , = number of individuals of species ,and = total number of individuals [ ]. Pearson correlation was conducted to determine the relationship between the soil physicochemical factors and species richness and diversity.

Results
Table shows the di erent plant species, their code, authors a n dl i f ef o r m sf o u n di nt h es t u d ys i t e s( A t u l l a h ,L e l e n g , Mbindia, and Nyitebong). A total of species were recorded in all the four sites belonging to families and genera in which % were identi ed to species level and % identi ed to genus level. Out of the species identi ed in the study sites, species were treelets, mostly < m tall, and species were understory trees < m tall and seldom reaching the canopy. Twenty-ve ( ) species were main canopy species and species were emergent trees species.
From the families recorded in the study sites, the Rubiaceae had the highest number of genera ( ) and species ( ) followed by the Sterculiaceae with species and genera. A total of genera were recorded in the study sites. Cola (Rubiaceae) were the most abundant genera with the highest number of species ( ). is was followed by the genera Strombosia (Olacaceae) and Ver nonia (Asteraceae) having species each (Table ).
Table shows the di erent trees species found in the di erent study sites and their relative abundance. In the four sites, individuals were sampled. e species with the highestnumberofindividualwasMacaranga monandra ( ) with a relative abundance of . %. It was followed by Pentadesma butyracea ( individuals and relative abundance   In Nyitebong, species were recorded from families and genera. e most abundant species were Pentadesma butyracea ( individuals) and Gaertnera paniculata ( ) with several families having only one species representative. Allanblackia gabonensis (Clusiaceae), Beilschmiedia sp (Lauraceae), Cola megalophylla (Sterculiaceae), Diogoa zenkeri (Olacaceae), Piptostigma oyemense (Annonaceae), Pycnanthus angolensis (Myristicaceae), Spathodea campanulata (Bignoniaceae), and Kigelia africana (Bignoniaceae) were rare species having only one individual recorded in the area.
In Mbindia, species were recorded from families and genera. e most abundant species were Cola heterophylla ( individuals) and Dracaena arborea ( i n d i v i d u a l s ) . er a r es p e c i e sh a v i n go n l yo n ei n d i v i dual included Craterispermum aristatum (Rubiaceae) and Microdesmis puberula (Pandaceae), which was found only in Mbindia.
In Atullah, species were recorded from families and genera. e most abundant species were Maesa lanceolata ( individuals) and Xymalos monospora ( individuals) while Balanophora coriacea (Rubiaceae) was the only rare species.
In Leleng, species were recorded from families and genera. e most abundant species were Macaranga monandra ( individuals) and Vernonia conferta ( indiv i d u a l s ) . er a r es p e c i e sh a v i n go n l yo n ei n d i v i d u a la n d occurring only at Leleng included Euphorbia desmindi (Euphorbiaceae) and Piper capense (Piperaceae).

. . Diversity.
e Shannon-Weaver Diversity Index ( ὔ ), Pielou's Evenness, and the species richness ( )ofthedi erent study sites are shown in Table .N y i t e b o n ga n dM b i n d i a submontane forests were the most diverse communities with Figure shows the di erent diameter classes found in the di erent study sites. e diameter range was grouped as small trees ( -. cm), medium-sized trees ( . -. cm), and large trees (> . cm). e four sites were dominated by trees species having diameters ranging from to mm (small trees). Medium-sized trees were also present in all the sites.
In Nyitebong, trees ( . %) with DBH range ofmm and trees ( . %) with DBH range of -mm were recorded. In Leleng, trees ( . %) with DBH range of -. cm, trees ( . %) with DBH range of -. cm, and trees ( . %) with DBH ≥ cm were recorded. In N y i t e b o n g , t r e e s( . % )w i t hD B Hr a n g eo f -. c m , trees ( . %) with DBH range of -. cm, and trees ( . %) with DBH ≥ cm were recorded. In Mbindia, trees ( . %) with DBH range -. cm, trees ( . %) with DBH range of -. cm, and trees ( . %) with DBH ≥ cm were recorded. Figure   and . %, respectively. Soils at Attuleh had almost the same soil texture percentages while in Leleng the montane had high clay content ( . %) compared with the submontane with . % clay and . % of silt. Table shows the correlation between soil parameters, diversity indices, index of evenness, and species richness. e diversity and evenness of plants in study sites were negatively correlated with pH while there was no correlation with species richness ( > 0.01 and > 0.05, resp.). Evenness was positively correlated with calcium and ECEC ( > 0.05). e diversity of plants was positively correlated with Bray phosphorus content of the soil ( > 0.05).

Discussions
. . Species Diversity in the Study Sites.
e forests of southwestern Cameroon are generally known to be rich in species diversity because they are located within the high rainfall zone of the Guinean equatorial tropical forest. Tropical forest contains more than half of the global species diversity, and it is o en subjected to increasing anthropogenic pressure which leadst olos so fb iodi v er si ty[ ]. It is also believed that this area formed a Pleistocene refugium during the last glacial International Journal of Biodiversity T : Correlation between soil and diversity parameters. International Journal of Biodiversity period,beco mingisola tedandallo wingthedevelo p men to f regional endemic species [ ].
In the study area, the most dominant family was the Rubiaceae, and this implies that the Rubiaceae could be the most dominant tree family in the Guinean equatorial forest.
is Twenty-eight ( ) species of plants were found only in the submontane forest, while plant species were found only in the montane forest. is high number of species found in the submontane area could be due to the disturbance (agriculture) which brings about the establishment of secondary species [ ]. irteen ( ) species of plants cut across all the study sites and the ecology of these species show that they thrive across a wide range of habitats including both montane and submontane habitats.
Allanblackia gabonensis is a rare species occurring only at Nyitebong. e absence of this species in the other sites might be due to deforestation. At these sites (Mbindia, Atullah, and Leleng) human activities particularly agriculture (slash and burn farming system) were higher than those in Nyitebong.

Allanblackia gabonensis is of particular interest because it is vulnerable and of great economic value. is result is in line with the ndings of Ndam et al. [ ]whoalsoreported
Allanblackia gabonensis to be a rare species in the Mount Cameroon montane forest.
. . Species Richness and Diversity. According to Kent and Coker [ ], a forest community is said to be rich if it has aS ha nn o nDi v er si tyval ue≥ . . All our sites had Shannon-Weaver Diversity indices values below . making the forest relatively poor in diversity. e submontane forest at Nyitebong was the most diverse and also the most even forest of all the four study sites followed by the submontane forest at Mbindia. is could be due to the fact that forests at Nyitebong and Mbindia were relatively undisturbed through anthropogenic factors such as agriculture and hunting. Seco n d l yi tm i g h ta l s ob ed u et ot h ea b a n d o n m e n to ff a r m i n g activities by the peasants and the successional changes in the vegetation as lands had been le to fallow for a very long time in both areas [ ]. is had resulted in the reappearance of many plant species in this area. e submontane forest at Leleng was the least diverse of all the sites. is might be due to anthropogenic e ects. In the Leleng area, cultivation, hunting, and collection of forest products were the main activities of the local population. Also we observed large plantations of cocoyams cultivated around the forest edges, and this crop is the main staples of the local community around the forest and is also their source of incoming, hence increasing the pressure on the surrounding forest [ , ]. e action of the local people has led to untold su ering including homelessness loss of human lives, properties, and forest land, substantial loss of biodiversity, habitats, and loss of income sources leading to extreme levels of poverty [ , ]. ere is also loss of cultural values and serious degradation of habitats.
. . reatened Species in the Study Sites.
e majority of the taxa found in the studied area are of conservation value and importance. ey occur mostly in the intricate mosaic of lowland and ridge forest formations, and the ecological fragility and anthropogenic pressure on the montane forest and submontane forest suggest that these ecotypes are of considerable conservation value. Out of the species recorded, species were threatened. ese species included Allanblackia gabonensis, Vepris trifoliolata, Sche era hierniana, Xylopia africana, Guarea thompsonii, and Cyclomorpha solmsii, and these were all vulnerable species according to IUCN [ ].
e presence of these species in the study sites could be because this area is within the Mount Cameroon region which is reported to be a centre of biodiversity and endemism in Cameroon [ ]. Scholes and Biggs [ ]a l s of o u n dt h a t montane forest contains several centre of endemism for birds, mammals, and plants.
e oristic composition and the threatened/endangered species found in the IUCN categories show that this area is qualitatively diverse. e occurrence of threatened species in the area might also be due to the accidental nature of the terrain which restricted human activities especially agriculture to areas that were relatively accessible, thus allowing the inaccessible areas to be relatively undisturbed. Some of the threatened species such as Guarea thompsonii, Cyclomorpha solmsii, and Sche era hierniana were used in the area as timber, medicine, and fencing, respectively, and this could be the reason why these species did not appear in all the study sites. e following species: Xymalos monospora, Tricalysia atherura, and Piptostigma oyemense which are endemic to Cameroon were also recorded in our study area.
. . Substrate Parameters. Based on studies of soil properties, phosphorus present in most tropical soils is lacking due to soil acidity, and xation therefore becomes unavailable to plants forpropergrowthanddevelopment[ ].
Forest ecosystems are highly diversi ed in plant species a n dt h i sg r e a t o r i s t i cd i v e r s i t yi ss u p p o r t e db yr e l a t i v e l y poor and acidic soils [ ]. Nyitebong was the most diverse of all sites having very acidic soils that have low calcium, magnesium, potassium, and sodium concentrations. is result corroborates the ndings of Fonge et al. [ ]w h o reported similar results in soils of the Mount Cameroon region. Nyitebong submontane forest also had the highest values in terms of carbon: nitrogen ratio, organic carbon, total nitrogen, Bray phosphorus, and CEC, and this explains its high oristic diversity. e high content of these elements couldbebecauseofthecontinuousaccumulationoforganic material on the top soil over the years from pioneer species (bryophytes, ferns, orchids, etc.), litter from trees, shrubs, and dead macro-and microorganisms which could be responsible for the regeneration of the vegetation cover [ , ]. Nyitebong submontane had the highest percentages of organic carbon, and this might be the reason why they had a greater diversity compared with the other sites.

International Journal of Biodiversity
Pearson correlation shows that organic carbon was positively correlated with the total nitrogen and the carbonnitrogen ratio. ese two nutrients are essential macronutrients for plant growth and vegetation establishment. e humid substances from the decay of organic materials aid in weathering of the parent rock and thereby increasing the amount of silt and clay in the soil. Nevertheless, this was not the case in Nyitebong where the sand content was high and this high content of sand could be attributed to the composition of the parent rock material and the weathering processes involved during soil formation and high rainfall which causes the leaching of nutrients from the soil. Leleng montane forest unlike most montane ecosystems had soils with high clay content. is might be due to the fact that the slope at Leleng was not steep and thus reducing the rate of erosion. Diversity was positively correlated with phosphorus concentration in the soil while it was negatively correlated with the pH. Evenness was negatively correlated with pH and positively correlated with ECEC and the calcium content of the soil. Potassium did not correlate with any of the parameters meaning that potassium did not in uence the diversity and distribution of species in the study area. Phosphorus concentration of the soils ( . ppm) was the highest in Nyitebong submontane, but this value was relatively low compared with the ndings of Mvondo Ze [ ]whoreported the phosphorus content of Mount Cameroon soils to be between and ppm. e low phosphorus concentration of soils in the study sites might be the reason for the low diversity in the area. Phosphorus was negatively correlated with pH in our study sites, and this was in line with the ndings of Wada and Gunjigake [ ] who reported that the amount of phosphorus in soils is correlated with the pH of the soil.

Conclusion
Biodiversity is in need of wise management not only to satisfy international pressures and obligations, but also because biodiversity could be the basis of most rural sustainable livelihoods in new economic sectors. e montane and submontane vegetation was subjected to human disturbance. I nth eLe b ial e mr e gi o n ,m o s to fth etr ees pec i e sa r etr ee l e t s with a height range of about < m signifying anthropogenic disturbance. Rubiaceae was the most common family with Cola being the most abundant genera followed by Strombosia (Olacaceae) and Ver nonia (Asteraceae). e tree species were greatly a ected by the soil physicochemical properties and were positively correlated with Bray phosphorus.

Recommendations
e population needs to be educated on sustainable farming techniques (e.g., agroforestry that maximizes production in reduced surface area) and sustainable forest management.
is will help reduce the pressure on the forest and thus conserving the natural environment.
More research should be geared towards e ects of climate and landuse changes factors on vegetation establishment in this area as this will help in the management of landslide activities in these ecosystems.  [ ] IUCN, Guidelines for Application of IUCN Red List Criteria at