Lyonia:
a journal of ecology and application


Vegetation and soil status on an 80 year old lava flow of Mt. Cameroon, West Africa
Vegetación y estado de los suelos en un flujo de lava de 80 años en Mt. Camerún, Oeste de África.

Fonge B. A.1*; Yinda G.S.1; Focho D.A.2;Fongod A.G.N.1 Bussmann R.W.3

1University of Buea, P.O. Box 63 Buea, Southwest
Province, Cameron, Email: bambofonge@yahoo.com,
*Author for correspondence, yinda_sendze@hotmail.com,
tina_fongod@yahoo.com

2University of Dschang, P.O Box 217 Dschang, Cameroon,
Email: dafocho@yahoo.fr

3University of Hawaii, Harold L. Lyon Arboretum, 3860
Manoa Rd. Honolulu, HI 96822, USA. Email: bussmann@hawaii.edu
Abstract 
Vegetation surveys were carried out in 2001-2002 on the 1922 lava flow on Mount Cameroon in order to assess species richness and soil status. A total of 102 species were recorded belonging to 47 families, including 21 tree species belonging to 13 families, 13 shrubs belonging to seven families, 20 herb species belonging to 10 families, seven climbers belonging to five families, 17 ferns belonging to eight families, five moss species, four lichen species, 13 orchids species and two fungi species. The family Orchidaceae was the most represented herb family while Rubiaceae was the most represented tree family. A total of 106 trees with dbh from 1 - 10 cm were recorded, with mean dbh of 6.65 cm and mean total BA of 1885.3 cm2 recorded. Syzygium guineense had the highest BA (769.68 cm2), with highest relative density (16.807%), relative dominance (40.83%) and CVI (57.638%) with an Important Value Index = 68.24%). Alchornea cordifolia with BA = 537.21cm2 had a relative density = 15.966%, relative dominance = 28.495%, CVI = 44.462%, and IVI of 55.57. Mangifera indica had the least with BA = 0.785 cm2, relative density = 0.821, Relative dominance = 0.042, CVI = 0.882 and IVI = 2.84%. Chromolaena odorata, Nephrolepis pumicicola, Nephrolepis biserrata were frequent with Nephrolepis pumicicola having the highest density (3.35%) and 13.87% relative density. Alstonia boonei and Maytenus sp. had the lowest densities. Shannon-weaver diversity (H1) and Simpson diversity indices are 3.58 and 22.863 respectively. The physico-chemical parameters of the soil from the edges and the centre of the lava were analysed. Colour ranged from very dark grey (5y 3/1), in the centre, to dark reddish brown (5y 3/3, 5y 3/4). The topsoil was mostly made up of organic matter. The soils were acidic (pH from 4.62 - 5.31), soil sand content was highest at the right edges (56.5%) and lowest at the centre (16.8%). Total Nitrogen was found to be highest on the lava centre, (3.53%), and lowest at the right edge (1.65%) while the total phosphorus was highest at the left edge (27.15) and lower (19.3) on the centre; being relatively higher than all other soils in Cameroon (12 - 16%), Calcium (Ca) is relatively high in the complex and shows the highest percentages among all cations. The principal component analysis showed that PC1 (69.3%) is most strongly affected by total Nitrogen, exchangeable cations, CEC, organic carbon and organic matter, while PC2 (30.70%) is strongly associated with total phosphorus (Bray II) and sand silt content. These are the main factors that influence vegetation growth on this lava.
Resumen 
La vegetación en el flujo de lava de 1922 del Mt. Camerún, fue estudiado entre 2001-2002 para investigar la riqueza de especies y el estado de suelo. Se encontraron 102 especies de plantas de 47 familias, incluyendo 21 especies de árboles en 13 familias, 13 arbustos pertenecientes a siete familias, 20 hierbas en 10 familias, siete trepadoras en cinco familias, 17 helechos en ocho familias, cinco briofitos, cuatro líquenes, 13 especies de orquídeas y dos en hongos. Las orquídeas representan la familia más importante de hierbas, mientras que las Rubiaceas son la familia más rica de árboles. Se encontró un total de 106 árboles con dap de 1-10 cm., y un dap medio de 6.65 cm., y un total de área basal (AB) de 1885.3 cm2. Syzygium guineense tuvo la AB más alta (769.68 cm2), la densidad relativa más alta (16.807%), dominancia relativa (40.83%) y CVI (57.638%) con índice de valor de importancia (IVA) = 68.24%. Alchornea cordifolia con BA = 537.21cm2 , densidad relativa de = 15.966%, dominancia relativa = 28.495%, CVI = 44.462%, y IVA de 55.57. Mangifera indica tuvo la AB mas pequeña con 0.785 cm2, densidad relativa = 0.821, dominancia relativa = 0.042, CVI = 0.882 y IVA = 2.84%. Chromolaena odorata, Nephrolepis pumicicola, Nephrolepis biserrata estuvieron frecuente con Nephrolepis pumicicola con la densidad más alta (3.35%) y 13.87% densidad relativa. Alstonia boonei y Maytenus sp. Tuvieron la densidad mas baja. Los índices de Shannon-weaver (H1) y Simpson fueron 3.58 y 22.863. Los parámetros físico-químicos de los suelos de los límites y del centro del flujo de lava fueron analizados. El color estuvo entre (5 y 3/1) en el centro hasta (5 y 3/3, 5 y 3/4). El primer horizonte del suelo consistió de materia orgánica. Los suelos se muestran ácidos (pH de 4.62 - 5.31), y el contenido de arena estuvo mas alto en los limites (56.5%) y mas bajo en el centro (16.8%). El Nitrógeno total estuvo mas alto en el centro (3.53%), y mas bajo en el lado derecho (1.65%) mientras que el fósforo estuvo mas alto en el lado izquierdo (27.15%) y mas bajo (19.3%), una cantidad mas alta que en suelos normales de Camerún (12 - 16%).
Introduction 

Mt Cameroon is located in the Gulf of Guinea at the South West Province of Cameroon. Its longest axis, as shown in [[Figure1]], about 45 km long and 30 km wide runs SW to NE between latitudes 3°57' to 4°27'N and longitudes 8°58' to 9°24'E, with the main peak at 4°7'N and 9°10'E (Tchouto, 1996; Suh et al., 2003). It is considered to be one of the most active volcanoes in Africa, having erupted eight times within the past 100 years (1909, 1922, 1925, 1954, 1959, 1982, 1999 and 2000). Soils on Mt Cameroon are mostly of recent age and derived from active volcanic rocks. They are generally fertile but have a poor moisture retaining capacity (Cheek, 1992). The soil temperature, measured at depths of 10 cm, varies from 25°C (at 200 m) through 20°C (at 1100 m) to 15°C at 2200 m above sea level (Payton, 1993). The region has two main seasons: a wet season with heavy rains from June to October and a dry season from November to May. The mean annual rainfall of this area varies between 2085 mm, near Ekona on the leeward side, to 9086 mm at Debundscha on the windward side of the mountain. This is the wettest place in Africa (Fraser et al., 1999). Mean monthly temperatures, at sea level, vary from 19°C to a maximum at 30°C during the months of March and April (Fraser et al., 1998). The humidity range is between 75% and 80% throughout the year on the southwestern side of the mountain. The persistent cloud cover and mist make Mt Cameroon one of the areas, receiving the lowest annual sunshine in West Africa. Sunshine ranges from 900 to 1200 hours/year at sea level and decreases with altitude (Payton, 1993). Plant recovery on the different lava flows has resulted in a rich and mosaic type of vegetation on the mountain slopes. There have been a number of publications on the geology of the mountain and most of the eruptions of the twentieth century (Deruelle et al., 1987; Fitton et al., 1983; Géze, 1943; 1953; Suh et al., 2001; 2003). Very few studies have been concerned with reporting plant recolonisation of Mt Cameroon (Keay, 1959; Benl, 1976; Fraser et al., 1998; Ndam et al.; 2002). No studies so far have attempted to establish any relationship between the plant diversity and the soil nutrient status of any of the lava flows.
The present study thus aims at updating plant inventories on the 1922 lava flow and reporting on the present nutrient status of the soil 80 years after the eruption.

Fig. 1: Map showing the different lava sites on Mt. Cameroon



Materials and Methods 

The eruption studied occurred from 2nd February and ended on 24th August 1922. It occurred in two locations, at 30-50 m above sea level (asl) (2nd -19th Feb) and between 900-1050 m asl (3rd of March - 24th August) (Haig, 1937; Géze, 1943; Fitton et al., 1983 and Déruelle, 1983). The lava flow is located at 9°1'W, 4° 1'N, 2 km south of Idenau and 10 km north of Debundscha. The lava is basaltic and typically pahoe-hoe lava, resulting from two viscous, fast flowing lava. The lava is smooth and has a ropy appearance. The surface of the lava now has plants and appears slimy and silky. Mean annual rainfall at Idenau is 8,392 mm, and that of Debundscha is 9086 mm (Fraser et al., 1998). The rainfall pattern is monomodal. The lava emerged from a crater at about 1,500 m asl, and moved 10 km from the crater to the sea. The flow is 1.5 km wide until it becomes divided at 170 m asl.




Fifteen plots of 20 m x 50 m, at a distance of 100 m from each other were located on the two edges, (1 plot each) and 13 plots in the centre of the flow. The plots were then surveyed using the Whittaker method as shown in [[Figure 2]] (Bullock, 1996). Plots were completely sampled in July 2001(rainy season), December 2001 (dry season), June 2002 and December 2002.
Plant species found on the different plots were identified, and their growth forms and distribution patterns noted. For each species, the number of individuals encountered in the plots was recorded. Information on modes of dispersal was obtained from collections from the Limbe Botanic Garden and other available literature. Voucher specimens were prepared, identified and deposited at the Limbe Botanic Garden herbarium (SCA).

Fig. 2: Plot Layout by Whittacker's method




Topsoil samples at 0-5 cm depth were collected from each of the plots in triplicates and bulked. Using standard procedures the following soil characteristics were determined.
Soil texture, Soil reaction (pH in H2O and in KCL), Organic Matter and Organic Carbon using the Walkley and Black method (Cottenie et al., 1982), Total Phosphorous, (using Bray's II method), Total Nitrogen was determined using a modified Kjedahl method, Exchangeable cations (Ca, Mg, K, and Na) were extracted and read using the Atomic Absorption. Spectrophotometer (AAS), CEC was determined using 1M Ammonium Acetate at pH 7 and 1 M KCl at pH 8.2, Amorphous Fe and Al using colorimeter (Blakemore et al., 1981), Free Fe, Mn, Zn and Cu using AAS, Phosphorus retention (Blakemore et al., 1987).



The Minitab (13.1) was used to analyse data collected.
Plant species were sorted out into different life forms. The species diversity was determined using Shannon-Weaver Diversity Index (H+):
Hi=-Σ(pi)(ln pi)
Where pi = proportion of all individual in the samples belonging to species i (Magaurran, 1988).


Simpson's Diversity Index (1/D), was also used to compute the diversity of the species.
Where D = Σ (pi) 2
Jaccard's coefficient was used to calculate the similarity indices of species between plots in the lava.
Jaccard's coefficient
(Cj) = J / (a = b - j)
Where
J = Number of species common to both sites.
a = Number of species in site A
b = Number of species in site B (Fowler et al., 1998; Krebs, 1999)


Species composition, basal areas and densities were also calculated.
The soil data were analysed using principal component analysis.


Results 


A total of 102 species belonging to 40 families were collected (Table 1 and Appendix 1). Seventy-four (74) of them were flowering plant species (belonging to 29 families), with 21 tree species belonging to 13 families, 13 shrubs belonging to 7 families, and 33 herbaceous species including 13 orchids belonging to 11 families, 7 climbers (belonging to 5 families), 17 fern species (belonging to 8 families), 5 mosses, 4 lichens, and 2 unidentified fungi species were also collected.
Table 1: Species abundance on the 1922 lava flow classified by family and life forms




Different Lifeform
No of Families No of Species



Flowering plants
29

74






Climbers
5

7






Herbs
10

20






Orchids
1

13






Shrubs
7

13






Trees
13

21






Ferns
8

17






Fungi
1

2






Lichens
1

4




Mosses
1

5





Total

47

102






[[Figure 3]] shows, that the Orchidaceae was the most represnted family, with 13 species, while the Rubiaceae was the most represented tree family with 8 tree species. The Asteraceae, Poaceae, and Musci had 5 species each. Six other families had 3 species, 5 with 2 species and 18 with only a single species.


Table 2 shows 106 trees with dbh between 1-10 cm, belonging to 18 species and 10 families. The mean dbh was 3.65 cm and the mean total basal area (BA) was 1885.3 cm2.






Table 3 shows some quantitative characteristics of the vegetation found on the 1922 lava flow. The basal areas (BA), ranged from less than 1 cm2 in Mangifera indica to over 500 cm2 in Alchornea cordifolia. Relative densities (relden) value were generally less than 10%) except for Syzygium guineense that had the highest relative density (16.81 %), a relative abundance of 40.83 %, CVI. of 57.63 % and IVI of 68.74%. Mangifera indica had the lowest, relative density (0.84 0%), relative abundance (0.42 %) and CVI (0.88 %).



Species similarities between the different plots in the lava are shown in [[Figure 4]] and Appendix II. The distance correlation coefficient (ward linkage) showed that the lava has two main types of plant communities based on their similarity indices. The first type includes plots 1, 2, 3, 5, 6, 4 and 7. The main species peculiar to this community include Croton gratissimus, Melanthera scandens, Ageratum conyzoides, Elaeis guineensis, Psorospermum standis, Harungana madagascariensis, Solenostemon monostachyus and Dissotis rotundifolia. The main plant species belonging to the second type include Centrosema virginianum and Trichomanes africanum.


Fig. 3 Frequency of Plant Species found of different Families and Groups on the 1922 lava flow




No Species Family Codes Lifeform No of Plants (nb) DBH (cm)

1

Albizia zygia

Leguminosae/Mimosaceae

Alzy

Tree

3

3

2

Alchornea cordifolia

Euphorbiaceae

Alco

Tree

19

6

3

Alstonia boonei

Apocynaceae

Albo

Tree

1

2.2

4

Bridelia micrantha

Euphorbiaceae

Brmi

Tree

3

3

5

Cecropia cecropioides

Cecropiaceae

Cece

Tree

7

5

6

Ficus lutea

Moraceae

Filu

Tree

7

5

7

Ficus sur

Moraceae

Fisu

Tree

5

3.5

8

Harungana madagascariensis

Guttiferae/Clusiaceae

Hama

Tree

6

3.5

9

Mangifera indica

Anacardiaceae

Main

Tree

1

1

10

Musanga cecropioides

Cecropiaceae

Muce

Tree

4

3.8

11

Psidium guajava

Myrtaceae

Psqu

Tree

2

2.3

12

Syzygium guineense

Myrtaceae

Sygu

Tree

20

7

13

Syzygium sp.

Myrtaceae

Sysp

Tree

2

3.8

14

Trema orientalis

Ulmaceae

Tror

Tree

2

1

Mean dbh = 3.65 cm
Table 2: Families with tree species with DBH 1-10cm in the 2001-02 surveys on the 1922 lava flow.




Species Family Code Life forms BA (cm2) Relden (%) RelDom (%) CVI (%) Freq RelFreq IVI (%)

Macaranga occindentalis

Euphorbiaceae

Maoc

Tree

3.14

0.84

0.17

1.01

1

0.79

1.80

Alstonia boonei

Apocynaceae

Albo

Tree

3.80

0.84

0.20

1.04

1

0.79

1.84

Mangifera indica

Anacardiaceae

Main

Tree

0.79

0.84

0.04

0.88

2

1.59

2.47

Trema orientalis

Ulmaceae

Tror

Tree

1.57

1.68

0.08

1.76

2

1.59

3.35

Hymenodictyon biafranum

Rubiaceae

Hybi

shrub

3.54

1.68

0.19

1.87

3

2.38

4.25

Psidium guajava

Myrtaceae

Psqu

Tree

8.31

1.68

0.44

2.12

4

3.18

5.30

Tetracera alnifolia

Dilleniaceae

Teal

Tree

2.356

2.52

0.13

2.65

4

3.18

5.82

Albizia zygia

Leguminosae/Mimosaceae

Alzy

Tree

21.21

2.52

1.13

3.65

3

2.38

6.03

Bridelia micrantha

Euphorbiaceae

Brmi

Tree

21.21

2.52

1.13

3.65

3

2.38

6.03

Syzygium sp.

Myrtaceae

Sysp

Tree

22.68

1.68

1.20

2.88

7

5.56

8.44

Psorospermum staudtii

Guttiferae/Clusiaceae

Psst

shrub

12.57

3.36

0.67

4.03

6

4.76

8.79

Musanga cecropioides

Cecropiaceae

Muce

Tree

45.37

3.36

2.41

5.77

7

5.56

11.32

Ficus sur

Moraceae

Fisu

Tree

48.11

4.20

2.55

6.75

10

7.94

14.69

Mussaenda tenuiflora

Rubiaceae

Mute

Climber

7.85

8.40

0.42

8.82

10

7.94

16.76

Harungana madagascariensis

Guttiferae/Clusiaceae

Hama

Tree

57.73

5.04

3.06

8.10

11

8.73

16.83

Cecropia cecropioides

Cecropiaceae

Cece

Tree

137.44

5.88

7.29

13.17

5

3.97

17.14

Tarenna conferta

Rubiaceae

Taco

Shrub

43.26

14.28

2.29

16.58

7

5.56

22.14

Ficus lutea

Moraceae

Filu

Tree

137.44

5.88

7.29

13.17

12

9.52

22.70

Alchornea cordifolia

Euphorbiaceae

Alco

Tree

537.21

15.97

28.49

44.46

14

11.11

55.57

Syzygium guineense

Myrtaceae

Sygu

Tree

769.69

16.81

40.83

57.63

14

11.11

68.74





























TOTALS


1885.3 100 100 200.00 126 100.00
Table 3:The basal area, relative densities, relative abundances, cover value indices, frequencies, relative frequencies and the important value indices of species on the 1922 lava flow.

Fig. 4: Dendrogram showing similarity between different plots on the 1922 lava flow





The soil profile of the lava flows is given in Table 4 below.


Table 4: The soil profile of the 1922 lava flow on Mt Cameroon.





Parameter


Centre


Right edge


Left edge



Colour



Very dark grey (5Y311)



Dark reddish brown (5Y313)



Dark reddish brown (5Y3/4)



Top Soil



More organic matter about (1 cm thick)



Sandy loamy soil (3cm thick)



Loamy soil, silt moisture with clay about 3.5cm thick



Horizon B.



Hard parent rock



Gravel thin layer



Gravel thin layer.




The chemical and physical properties of soils collected from the edges and the centre of the lava flow are given in Table 5.


Texture
Table 5 shows that the sand content was highest on the right wing, with 56.5 % sand, while the centre and the left edges had 16.8 % and 19.3 % respectively. There is no front since this lava flowed into the sea. Silt is highest in the left wing (69 %), while it is lowest in the right wing (39 %). The clay content is highest in the centre (15 %) and lowest in the right wing (5 %).









Particle Size Analysis %



PH

Organic Matter











Sand


Silt


Clay


H2O


KCl


%C


%N


C/N
%P Retention
Total
%P

Centre

16.8

68

15

4.62

4.31

1.10

3.53

31.4

51.02

19.30

Right Wing

56.5

39

5

5.31

4.66

4.44

1.65

27.0

50.64

21.88

Left Wing

19.3

69

12

5.05

4.55

3.70

2.40

15.4

48.20

27.13


Exchangeable
Cations

Meq/100g



Micronutrients
%







Ca


Mg


K


Na
CEC Meq/100g Base Structure % Total Fe Liberated Fe Amorphous Fe Amorphous Al

Centre

2.72

0.56

1.44

0.08

4.81

9

1.69

7.63

3.02

5.34

Right Wing

2.89

1.16

0.28

0.01

3.34

13

0.92

4.82

10.81

5.66

Left Wing

2.42

0.44

0.28

0.03

3.19

11

0.00

8.9

3.85

5.66
Table 5: Chemical analysis of soil from the 1922 lava flow on Mt Cameroon





Organic Carbon (Org C)
A comparison of the sampled sites shows that the centre on the 1922 lava had the highest Org C, while the left wing had the lowest (3.7 %).



Organic Matter (OM)
In 1922 lava flow, the centre had the highest OM (19.1%) while the left wing had the lowest OM (3.7 %).



Total Nitrogen (Tot N)
The total N is highest in the 1922 lava flow (3.53 %). Comparing the different sites at the 1922 lava, the centre had the highest Tot N (3.53 %) while the right wing had the lowest (1.65 %).



Exchangeable Cations
On the 1922 lava, Ca content is highest on the right edge (2.89 Meq/100g) and lowest in the left edge (2.42 Meq/100g). In the case of Mg, it is highest at the centre (0.46 Meq/100g) and lowest on the right edge (0.16 Meq/100g). The centre was richest in K and Na (1.44 Meq/100g and 0.08 Meq/100g)



Phosphorus Retention (P-Ret)
The amount of phosphorus retained in the soil on the 1922 lava is low (51.02 %). At the individual sites, the 1922 lava's left edge had the lowest (48.2 %) and the lava's centre, the highest (51.02 %).



Iron (Fe)
No soluble Fe was registered on the left edge of the lava but there was 7.63% liberated Fe and 10.81% amorphous Fe in it.




Eigen-analysis (Table 6a.) shows that the first two components PC1 and PC2 explain 100% of the total variation. Table 6b indicates that PC1 is most strongly affected by the Na, K, CEC, base saturation, Org. C, and OM, Total Nitrogen, soluble Fe, and soil clay content. PC2 is strongly associated with Ca, C/N, P and sand-silt content.




The Principal Correlation Analysis of soil in relation to vegetation and sites shows that the main soil contents that affect vegetation are soil texture, Org C and OM, on the lava. In relation to vegetation composition and diversity, the soil sand content, Org C and OM, strongly affect vegetation development, while soil texture, pH (H2O, KCl and NaF), CEC, Base saturation, Total N and P, P-Retention, Fe, Soluble Fe, Liberated Fe, Amorphous Fe and Al are associated and closely related to vegetation development.



Discussion 

The 1922 lava flow is located on the west coast of Mt. Cameroon. In this area the rainfall pattern is mono-modal and high, especially in Idenau and Debundscha. Fraser et al., (1998) reported that Debundscha is the second wettest region of the world with a mean annual rainfall of 9,086 mm (from 1965 - 1993) after Charrapanjee in India.
Debundscha is only about 1 Km from the sea and the 1922 lava flow where the flux of the wet monsoon winds influence precipitation. With this high precipitation the soils do not completely get dry, even when it does not rain for some days (Cable and Check, 1998).
According to Juvik and Merlin (2001) the type of lava also affects colonization patterns. The pahoe-hoe favours more plant diversity than the aa lava. This is because the cracks and fissures in pahoe-hoe, favour accumulation of rainfall and trap inorganic and organic particles from the surrounding impervious lava surface while the aa lava boulder fields are ubiquitous. This results in a lack of plant growth. The pahoe-hoe cracks also have thermal properties more conducive for plant growth. This maybe due to the persistent cloud cover and mist coupled with high rainfall, temperature and distance from the seacoast (Payton, 1993).
Throughout the year, the temperature is between 22°C - 30°C in Debundscha at an altitude of about 20 m asl. In Idenau at 40 m asl it ranges between 20°C - 30°C (Fraser et al., 1998; Tchouto, 1996). This may be because there is a gentle breeze blowing from the sea and that the air movements are very slow, thus modifying the temperature. Cable and Cheek (1998) reported that there are no hurricanes in this region.
Table 6a: Eigen-analysis of the Correlation Matrix 1922 Lava






PC1

PC2

PC3
Eigenvalue
15.119

6.881

0.000
Proportion
0.687

0.313

0.000
Cumulative
0.687

1.000

1.000

Table 6b :





Variable PC1 PC2 PC3

C2

-0.185

-0.264

0.135

C3

0.169

0.287

0.023

C4

0.222

0.191

-0.099

C5

-0.254

-0.060

0.179

C6

-0.256

-0.033

0.333

C7

-0.257

-0.000

0.115

C8

0.244

-0.118

-0.144

C9

0.244

-0.119

0.263

C10

0.253

0.070

-0.130

C11

0.138

-0.321

0.125

C12

-0.011

-0.381

0.006

C13

0.215

0.209

-0.004

C14

0.251

-0.085

0.266

C15

0.257

0.022

0.097

C16

0.245

-0.116

-0.126

C17

0.245

-0.116

-0.126

C18

-0.152

0.307

0.055

C19

0.106

-0.348

0.001

C20

0.179

-0.273

0.139

C21

-0.180

-0.272

0.129

C22

-0.178

-0.275

-0.719

C23

-0.251

0.085

-0.160


Where







C2 = sand

C9 = Org. Matter (%)

C16 = S/CECE (%)

C3 = Total silt

C10 = Tot. N (g/kg)

C17 = CEC 7

C4 = Clay

C11 = C/N

C18 = Brays P2 (ppm)

C5 = pH H2O

C12 = Ca

C19 = P-ret (%)

C6 = pH KCl

C13 = Mg

C20 = Soluble Fe (g/kg)

C7 = pH NaF

C14 = K

C21 = Liberated Fe

C8 = Org. C (%)

C15 = Na

C22 = Amorphous Fe







C23 = Amorphous Al



The mean annual relative humidity, on this Southwestern flank ranges between 75 % and 80 %. Generally, the climate is of the equatorial regime covering the entire land of the Atlantic oceanic plain.
Rosevear conducted the first recolonization study on lava flows on Mt Cameroon in 1936 and 1937 on the 1922 eruption, fourteen years after it occurred (cited by Keay, 1959). Eighty years after the eruption, it is observed that the vegetation has moved from the mosses, lichens and ferns as observed by Rosevear, to a dominant shrubby forest with 74 flowering plant species belonging to 29 families, the family Orchidaceae being the most dominant. This is in contrast with the findings of Ndam et al. (2002), who stated after a survey, conducted in 1995, that in the third stage of succession, 90% of orchids disappear. The vegetation presently comprises of a semi- dense, forest 4-5 m tall with emergent that are 10-25 m tall. The co-dominant trees (about 40% of all those greater than 6 cm dbh recorded, and generally the tallest of all trees present) are Syzygium guineense var. littorale and Alchornea cordifolia. Fraser et al., (1999) and Ndam, (2000) reported the presence of Syzygium guineense, during their 1995 survey. Lannea was not observed during this survey. This may be as a result of logging for fuel wood, which has already started on the lava flow (fig 5). The main trees and large shrubs, in descending order of importance (% of all trees between 1-10cm dbh) are Syzygium guineense (16.81%), Alchornea cordifolia (15.97%) and Tarenna conferta (14.29%). Seedlings of Tarenna conferta, in shrub surveys conducted done by Fraser et al., 1999 and Ndam et al., 2002, were shown to dominate those of smaller woody plants.
Some of the species found in the centre of the lava flow were not present on the edges. Plant diversity was higher in the centre than the edges. This may be as a result of the lava flow being surrounded by palm plantations (Elaies guineensis) and also because of the age of the lava (Déreulle et al., 1987).
Shannon-Weaver and Simpson's Diversity Indices show that plant diversity is high as should be expected. They are 3.58 and 22.86 respectively, higher than those determined by Ndam et al. (2002) on the same lava in 1995 (3.1057 and 16.4201 respectively). This shows that plant diversity has increased. The Basal Area of 0.785m2/h was far less than that observed by Ndam (1998). This may be as a result of the logging for fuel wood that is going on in the area.
Species richness was highest on the edges probably because at this stage of succession, new species colonize from the edges. Thebaud and Stersberg (1997), while studying species colonization of 15, 48, 91 year old lava flows at Grand Bruté, la Reunion, observed that dispersal on the15 year old lava flow was stochastic but found that large sized plants on the old lava flows (e.g. 91 years) tended to grow from the edge at a very slow rate (less than 1 m per year). They also observed that most colonizing species are wind-dispersed. A similar observation was reported by Ndam et al., (2002) on the 1922 lava flow and by Robyns(1932) in Kiva and Krakatua. This could also be due to the thickness of the lava at the centre compared to the edges (Fitton et al. 1983).
The Dendogram produced from the similarity indices shows that plants of the same species and life forms were found both on the edges and in the centre. Although the lava is chemically uniform, its structure can be variable resulting in differences in the colonization process (Bachelery, 1981). Another possible reason given earlier by Robyns (1932) for these differences could be that erosion from adjacent land, deposits soil on the edges of lava flows, favouring the development of species that are not adapted to grow on the dry rock environment. This is in contrast with our findings. Species diversity is higher in the centre of the 1922 lava flow as a result of differences in the soil parameters. The amounts of organic matter and organic carbon from analyses were highest in the centre (19.10 and 11.10 % respectively). On the edges they were 4.07 and 7.1 % respectively. The main reason for the contrast of our findings with earlier reports may be that the lava is moving towards a more mature structure. The climatic conditions of the area could also be wielding an influence. According to Fraser et al. (1998), the area has the highest amount of rainfall in the country. This, coupled with the high temperature and humidity, leads to rapid decomposition of organic matter resulting in fast soil formation. The topography (gentle sloping and flat) and lava type (pahoe-pahoe) also influence disintegration of the surface rock and soil formation.
It could be said that the successional pathway on lava flow starts with lichens and mosses, followed by a second stage characterised by the presence of all other life forms, with woody species and climbers being the least abundant or even absent.




The profile of the lava flow is divided into 2 horizons. The topsoil is 10 cm dbh did not conform to this observation. Comparing the observed data on species composition, basal area and plant density on the lava with those of other researchers showed some differences, which may be attributed to the logging for fuelwood -already taking place there. This means that colonization may be very difficult to assess.
The edaphic factors; climate (temperature between 19°C - 34°C), rainfall (between 227 - 9086 mm) and soil, play a very vital role on the plant colonization process. Also, the type and number of plant species tend to improve the nutrient level of the soil although the plants are selective to the type and amount of nutrients utilized. The soil pH is slightly acidic and tends to break down parent rock materials. Growing roots of trees also tend to break down the parent materials releasing nutrients.
From our results it was found that soil texture, total Phosphorus, total Nitrogen, Organic matter, cation exchange capacity (CEC), exchangeable cations soil pH and Phosphorus retention strongly affect the plant colonization process on the lava flows of Mt Cameroon.



Acknowledgements 

Special thanks go to the University of Buea (which gave the initial grant used to carry out this work), University of Dschang (where all the laboratory analysis were carried out), and the Limbe Botanic and Zoological Garden (who made available facilities for use during this research).



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APPENDIX I
List of species on the 1922 lava flow classified by family and life forms











Family Plant Sp Code Life Mechanism


Names No Code Form of dispersal

1
Convolvulaceae
Ipomoea batatas (L.) Lam.



Ipba

Climber

Animal

2
Convolvulaceae
Ipomoea involucrata P. Beauv.



Ipin

Climber

Animal

3
Convolvulaceae
Ipomoea sp.
3
Ipsp

Climber

Animal

4
Dilleniaceae
Tetracera alnifolia Willd.
1
Teae

Climber

Animal

5
Leeaceae
Leea guineensis G. Don
1
Lequ

Climber

Animal

6
Passifloraceae
Adenia lobata (Jacq.) Engl.
1
Adlo

Climber

Wind

7
Rubiaceae
Mussaenda tenuiflora Benth.
8
Mute

Climber

Wind

8
Aspleniaceae
Asplenium barteri Hook.
1
Asba

Fern

Wind

9
Dryopteridaceae
Ctenitis dimidiata (Mett. Ex Kuhn)Tardieu
1
Ctdi

Fern

Wind

10
Hymenophyllaceae
Trichomanes africanum Christ.



Traf

Fern

Wind

11
Hymenophyllaceae
Trichomanes borbonicum Bosch
2
Trbu

Fern

Wind

12
Oleandraceae
Arthropteris cameroonensis Alston



Arca

Fern

Wind

13
Oleandraceae
Nephrolepis biserrata (Sw.) Schott



Nebi

Fern

Wind

14
Oleandraceae
Nephrolepis cordiflora
4
Neco

Fern

Wind

15
Oleandraceae
Nephrolepis pumicicola Ballard



Nepu

Fern

Wind

16
Ophioglossaceae
Ophioglossum reticulatum L.



Opre

Fern

Wind

17
Polypodiaceae
Anapeltis lycopodioides (L.) J.Sm.
4
Anly

Fern

Wind

18
Polypodiaceae
Microgramma owariensis (Desv.) Alston



Miow

Fern

Wind

19
Polypodiaceae
Microsorum punctatum (L.) Copel.



Mipu

Fern

Wind

20
Polypodiaceae
Microsorum scolopendria (Burm.f.)Copel



Misc

Fern

Wind

21
Selaginellaceae
Selaginella sp.
1
Sesp

Fern

Wind

22
Vittariaceae
Antrophyum mannianum Hook.



Anma

Fern

Wind

23
Vittariaceae
Loxogramme abyssinica (Baker)M.G.Price
3
Loab

Fern

Wind

24
Vittariaceae
Loxogramme lanceolata(Sw.)C.Presl


Lola

Fern

Wind

25
Fungi
Unidentified



0

Fungi

Wind

26
Fungi
Unidentified
2
0

Fungi

Wind

27
Commelinaceae
Commelina diffusa Burm.f.
1
Codi

Herb

Animal

28
Compositae
Chromolaena odorata (L.)R.M. King &H.Robinson



Chod

Herb

Wind

29
Compositae
Crassocephalum crepidioides (Benth.) S.Moore



Crcr

Herb

Wind

30
Compositae
Emilia coccinea (Sims.)G. Don



Emco

Herb

Wind

31
Compositae
Melanthera scandens (Schumach.& Thonn.)Roberty
5
Mesc

Herb

Wind

32
Compositae/Asteraceae
Ageratum conyzoides L.



Agco

Herb

Wind

33
Cyperaceae
Mariscus alternifolius Sensu Hooper
1
Maal

Herb

Animal

34
Euphorbiaceae
Phyllanthus amarus Schumach. & Thonn.
5
Pham

Herb

Animal

35
Fabaceae
Pueraria phaseolioides (Roxb) Benth.
3
Puph

Herb

Animal

36
Fabaceae
Centrosema virginiana (L.) Benth.
2
Cevi

Herb

Animal

37
Gramineae
Hyparrhenia rufa (Nees) Stapf.
5
Hyru

Herb

Wind

38
Gramineae
Panicum maximum Jacq.



Pama

Herb

Wind

39
Gramineae
Paspalum conjugatum Berg



Paco

Herb

Wind

40
Gramineae
Pennisetum hordeoides (Lam.) Steud.



Peho

Herb

Wind

41
Gramineae/Poaceae
Axonopus compressus (Sw.) P. Beauv.



Axca

Herb

Wind

42
Labiatae/Lamiaceae
Solenostemon monostachyus (P.Beauv.) Briq.



Somo

Herb

Wind

43
Marantaceae
Megaphrynium macrostachyum (Benth.) Milne-Redh.
1
Mema

Herb

Animal

44
Melastomataceae
Dissotis rotundifolia(Sm.)Triana



Diro

Herb

Animal

45
Piperaceae
Piper umbellatum L.
1
Pium

Herb

Animal

46
Rubiaceae
Diodia sarmentosa Sw.


Disa

Herb

Animal

47
Lichens
Coccocarpia sp.



Cosp

Lichens

Wind

48
Lichens
Dictyonema sp.



Disp

Lichens

Wind

49
Lichens
Leptogium sp.



Lesp

Lichens

Wind

50
Lichens
Parmelia laevigata
4
Pala

Lichens

Wind

51
Musci
Campylopus dusenii C.M



Cadu

Moss

Wind

52
Musci
Campylopus horridus Welw.&Duby



Caho

Moss

Wind

53
Musci
Ectropothecium afro-molluscum (C.M) Broth.Keay



Ecmu

Moss

Wind

54
Musci
Ectropothecium regulare (Brid.)Jaeg



Ecre

Moss

Wind

55
Musci
Sematophyllum calspitosum (Sw) Mitt Sensu lato H.n.Dixon
5
Seca

Moss

Wind

56
Orchidaceae
Ancistrochilus rothschildianus O'Brien



Anro

Orchid

Wind

57
Orchidaceae
Ancistrorhynchus cephelotes



Ance

Orchid

Wind

58
Orchidaceae
Angraecum birrimense Rolfe



Anbi

Orchid

Wind

59
Orchidaceae
Bulbophyllum bifarium Hook.f.



Bubi

Orchid

Wind

60
Orchidaceae
Bulbophyllum calvum Summerh



Buca

Orchid

Wind

61
Orchidaceae
Bulbophyllum calyptratum Kraenzl.



Buca

Orchid

Wind

62
Orchidaceae
Bulbophyllum intertextum Lindl.



Buin

Orchid

Wind

63
Orchidaceae
Bulbophyllum josephii (Kuntze) Summerh. var. josephii



Bujo

Orchid

Wind

64
Orchidaceae
Bulbophyllum simonii Summerh.



Busi

Orchid

Wind

65
Orchidaceae
Hebenaria sp.
13
Hesp

Orchid

Wind

66
Orchidaceae
Polystachya affinis Lindl.



Poaf

Orchid

Wind

67
Orchidaceae
Polystachya tessellata Lindl.



Pote

Orchid

Wind

68
Orchidaceae
Polystachya laxiflora Lindl.


Polu

Orchid

Wind

69
Costaceae
Costus afer Ker Gawl.
1
Coaf

Shrub

Animal

70
Euphorbiaceae
Croton gratissimus Burch.



crhi

Shrub

Animal

71
Guttiferae/Clusiaceae
Psorospermum staudtii Engl.



Psst

Shrub

Wind

72
Malavaceae
Urena lobata L.
1
Urlo

Shrub

Animal

73
Melastomataceae
Dissotis erecta (Guill. & Perr.)Dandy



Dier

Shrub

Animal

74
Melastomataceae
Tristemma hirtum P.Beauv.
3
Trhi

Shrub

Animal

75
Mimosoidae
Mimosa pudica L.



Mipu

Shrub

Animal

76
Rubiaceae
Hymenodictyon biafranum Hiern



Hybi

Shrub

Wind

77
Rubiaceae
Oldenlandia lancifolia (Schumach.) DC.



Olla

Shrub

Animal

78
Rubiaceae
Pauridiantha venusta N.Halle



Pave

Shrub

Animal

79
Rubiaceae
Tarenna conferta (Benth.)Hiern



Taco

Shrub

Animal

80
Rubiaceae
Tarenna sp.



Tasp

Shrub

Animal

81
Rubiaceae
Tricalysia discolor Brenan


Trdi

Shrub

Animal

82
Anacardiaceae
Magifera indica L.
1
Main

Tree

Animal

83
Apocynaceae
Alstonia boonei De Wild.
1
Albo

Tree

Animal

84
Cecropiaceae
Cecropia cecropioides



Cece

Tree

Animal

85
Cecropiaceae
Cecropia peltata



Cepe

Tree

Animal

86
Cecropiaceae
Musanga cecropioides R.Br. ex Tedlie
3
Muce

Tree

Animal

87
Celastraceae
Maytenus sp.
1
Masp

Tree

Animal

88
Ericaceae
Agauria salicifolia (Comm.ex Lam.)Hook.f.ex Oliv.
1
Agsa

Tree

Animal

89
Euphorbiaceae
Alchornea cordifolia (Schum. $ Thonn.)Mull.Arg.



Alco

Tree

Animal

90
Euphorbiaceae
Bridelia micrantha (Hochst.)Baill.



Brmi

Tree

Animal

91
Euphorbiaceae
Macaranga occidentalis (Mull.Arg.)Mull.Arg.



Maoc

Tree

Animal

92
Fabaceae
Desmodium adscendens (Sw.)DC. var.adscendens



Dead

Tree

Animal

93
Guttiferae/Clusiaceae
Harungana madagascariensis Lam. Ex Poir.
2
Hama

Tree

Bird

94
Mimosaceae
Albizia zygia (DC.)J.F.Macbr.



Alzy

Tree

Wind

95
Moraceae
Ficus conraui Warb.
3
Fico

Tree

Animal/Bird

96
Moraceae
Ficus lutea Vahl



Filu

Tree

Animal/Bird

97
Moraceae
Ficus sur Forssk.



Fisu

Tree

Animal/Bird

98
Myrtaceae
Psidium guajava L.
3
Psqu

Tree

Animal

99
Myrtaceae
Syzygium guineense (Wild.)DC



Sygu

Tree

Animal

100
Myrtaceae
Syzygium sp.



Sysp

Tree

Animal

101
Palmae
Elaies guineensis Jacq.
1
Elgu

Tree

Animal/Rodents

102
Ulmaceae
Trema orientalis (L.)Blume
1
Tror

Tree

Animal



Appendix: II Similarity Index (Jaccard's) on the different plots in the 1922 lava flow.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
1 0 0.452 0.368 0.320 0.373 0.310 0.267 0.231 0.203 0.226 0.233 0.210 0.233 0.193 0.190
2.

0 0.467 0.544 0.361 0.281 0.403 0.387 0.361 0.367 0.356 0.328 0.379 0.321 0.316
3.



0 0.585 0.352 0.270 0.478 0.448 0.350 0.333 0.345 0.386 0.345 0.286 0.327
4.





0 0.319 0.250 0.567 0.463 0.382 0.442 0.431 0.423 0.404 0.340 0.360
5.







0 0.581 0.299 0.358 0.353 0.360 0.347 0.340 0.375 0.363 0.386
6.









0 0.224 0.333 0.325 0.300 0.316 0.342 0.389 0.419 0.452
7.











0 0.500 0.440 0.449 0.408 0.489 0.390 0.286 0.333
8.













0 0.583 0.600 0.742 0.719 0.543 0.500 0.581
9.















0 0.559 0.594 0.677 0.500 0.552 0.586
10.

















0 0.667 0.700 0.613 0.517 0.552
11.



















0 0.750 0.548 0.615 0.593
12.





















0 0.531 0.593 0.630
13.























0 0.500 0.536
14.

























0 0.850
15.



























0