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Landscape ecological survey (1 : 100 000)
of the Bipindi - Akom II - Lolodorf region,
southwest Cameroon
LANDSCAPE ECOLOGICAL SURVEY (1 : 100 000) OF THE
BIPINDI - AKOM II - LOLODORF REGION, SOUTHWEST
CAMEROON
B.S. van Gemerden
G.W. Hazeu
Tropenbos-Cameroon Documents 1
The Tropenbos-Cameroon Programme, Kribi (Cameroon)
DLO Winand Staring Centre, Wageningen (The Netherlands),
1999
ABSTRACT
Gemerden, van, B.S, G.W. Hazeu, 1999. Landscape Ecological Survey (1 : 100 000) of the Bipindi -Akom II -
Lolodorf region, Southwest Cameroon. Wageningen (The Netherlands), Tropenbos-Cameroon Documents 1 232 pp.;
... Figs; ... Tables; ... Refs; 6 Annexes.
In Southwest Cameroon a reconnaissance scale survey of landforms, soils and vegetation was carried out. The survey
area covered some 167 000 ha. The altitudinal range was 40 to 1 000 m.a.s.l. Landforms discerned are: mountains,
complexes of hills, isolated hills, hilly and rolling uplands, dissected erosional plains, and floodplains. Four soil types
were described, ranging from well drained very clayey soils (in the mountain area) to very poorly to poorly drained
soils (on valley bottoms). The seven main vegetation types include four types of primary to old secondary rain forest
(bound to different altitudinal zones), young secondary forest, swamp forest, and secondary shrubland. The patterns of
landforms, soil types, and vegetation types are integrated into one `landscape ecological' map (scale 1 : 100 000). The
legend has a hierarchical structure. It is based primarily on a subdivision in four altitudinal zones, secondly on
landform, and finally on the degree of disturbance of the natural vegetation by shifting cultivation.
Keywords: Africa, reconnaissance survey, rain forest, landforms, tropical soils, vegetation, altitudinal zonation.
ISSN 0927-4537
©1999 DLO Winand Staring Centre for Integrated Land, Soil and Water Research (SC-DLO) and The Tropenbos
Foundation
The Tropenbos Foundation, P.O. Box 232, NL-6700 AE Wageningen (The Netherlands)
Phone: 31 (317) 426262; fax: 31 (317) 423024; e-mail: tropenbos@iac.agro.nl
SC-DLO, P.O. Box 125, NL-6700 AC Wageningen (The Netherlands)
Phone: 31 (317) 474200; fax: 31 (317) 424812; e-mail: postkamer@sc.dlo.nl
No part of this publication may be reproduced or published in any form or by any means, or stored in a data base or
retrieval system, without the written permission of the DLO Winand Staring Centre or The Tropenbos Foundation.
The Tropenbos Foundation and SC-DLO assume no liability for any losses resulting from the use of this report.
CONTENTS
page
Preface 9
Summary 11
1 Introduction
13
1.1 Forest Land Inventory and Land Evaluation Project (Lu1)
13
1.2 Research objectives
13
1.3 Course of the study
13
1.4 Report outline
14
2 Study area
17
2.1 Location and infrastructure
17
2.2 Climate
17
2.3 Hydrology
19
2.4 Geology
21
2.5 Geomorphology
23
2.6 Soils
23
2.7 Vegetation
24
2.8 Wildlife
26
2.9 Population
26
2.10 Land-use
27
3 Methodology
29
3.1 Landscape ecological approach
29
3.2 Aerial photo interpretation
30
3.3 Fieldwork
30
3.3.1 General
30
3.3.2 Landform and soil
32
3.3.3 Vegetation
33
3.4 Classification
35
3.5 Legend and map compilation
36
4 Landforms
37
4.1 Literature review
37
4.2 Landform classification
37
4.2.1 Dissected erosional plains (pd)
38
4.2.2 Uplands (u1 and u2)
39
4.2.3 Hills (h1 and h2)
39
4.2.4 Mountains (m)
40
4.2.5 Valley Bottoms (v)
40
5 Soils
41
5.1 Literature review
41
5.2 Soil types and classification
42
5.2.1 Nyangong soils
43
5.2.2 Ebom soils
44
6
5.2.3 Ebimimbang soils
44
5.2.4 Valley Bottom soils
45
5.2.5 Soil classification
46
5.3 Soil physical characteristics
48
5.3.1 Texture
49
5.3.2 Bulk density
49
5.3.3 Water retention
50
5.4 Soil chemical characteristics
50
5.4.1 pH and exchangeable acidity
51
5.4.2 Organic carbon and total nitrogen
52
5.4.3 Available and total phosphorous
54
5.4.4 Cation exchange capacity and exchangeable bases
55
5.4.5 Clay mineralogy
56
5.4.6 Nutrient contents
57
5.4.7 Conclusions
58
5.5 Soil-landform relationships and soil genesis
58
5.5.1 Soil and landform relations
58
5.5.2 Soil genesis
60
6 Vegetation
63
6.1 Literature review
63
6.2 Botanical diversity
65
6.3 Vegetation classification
66
6.4 Plant communities
69
6.4.1 Maranthes - Anisophyllea community (I)
69
6.4.2 Podococcus - Polyalthia community (IIa)
71
6.4.3 Strombosia - Polyalthia community (IIb)
72
6.4.4 Diospyros - Polyalthia community (IIc)
73
6.4.5 Carapa - Mitragyna community (III)
74
6.4.6 Xylopia - Musanga community (IV)
75
6.4.7 Macaranga - Chromolaena community (V)
75
7 Landscape ecological map
77
7.1 Legend
77
7.2 Land use
77
7.3 Land mapping units
78
7.3.1 Am: mountains above 700 m asl, well drained soils
79
7.3.2 Ah1: isolated hills above 700 m asl, well drained soils
79
7.3.3 Bh2: complex of hills between 500 and 700 m asl, well drain soils
79
7.3.4 Bh1: isolated hills between 500 and 700 m asl, well drained soils
79
7.3.5 Bu2: hilly uplands between 500 and 700 m asl; well drained soils
80
7.3.6 Bu1: rolling uplands between 500 and 700 m asl; well drained soils
80
7.3.7 Ch1: isolated hills between 350 and 500 m asl, well drained soils
81
7.3.8 Cu2: hilly uplands between 350 and 500 m asl; well drained soils
81
7.3.9 Cu1: rolling uplands between 350 and 500 m asl; well drained soils
81
7.3.10 Dh1: isolated hills below 350 m asl, moderately well drained soils
82
7
7.3.11 Du2: hilly uplands below 350 m asl; moderately well drained soils
82
7.3.12 Du1: rolling uplands below 350 m asl; moderately well drained soils 82
7.3.13 Dpd: dissected erosional plains below 350 m asl; moderately well drained
soils 83
7.3.14 Ev: valley bottom; poorly to very poorly drained soils
83
References 85
Annexes
I Landscape ecological map of the Bipindi - Akom II - Lolodorf region, southwest
Cameroon (1 : 100 000) (separate)
II List of aerial photographs 1983 - 1985, 1 : 20 000 series covering
the TCP research area (Photosur Inc.)
91
III Methods for chemical and physical soil analysis
93
IV Soil profile descriptions and data of analysis
97
V Vegetation data
195
VI List of bird species observed in the TCP research area
219
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9
PREFACE
ABOUT TROPENBOS
The Tropenbos Foundation was established in 1988 by the Government of The Netherlands with
the objectives to contribute to the conservation and wise use of tropical rain forest by generating
knowledge and developing methodologies, and to involve and strengthen local research
institutions and capacity in relation to tropical rain forests.
The Tropenbos Programme carries out research on moist tropical forest land at various locations
around the world. At present (semi-) permanent research sites are located in Colombia, Guyana,
Indonesia, Côte d'Ivoire and Cameroon. At the different locations, research programmes follow
an interdisciplinary and common overall approach, with the aim to exchange data and make
results mutually comparable.
About the Tropenbos-Cameroon Programme and ITTO Project PD 26/92
The present publication has been produced in the framework of ITTO Project PD 26/92, which is
an integral part of the Tropenbos-Cameroon Programme (TCP). The research on which this
publication is based, was financed by the International Tropical Timber Organization (ITTO), the
Common Fund for Commodities (CFC), the Directorate General for International Cooperation of
The Netherlands' Ministry of Foreign Affairs (DGIS), the Tropenbos Foundation and the
implementing agencies mentioned below.
The Tropenbos-Cameroon Programme was established in 1992 by the Cameroonian Ministry of
Environment and Forests (MINEF) and the Tropenbos Foundation. The general objective of TCP
is to develop methods and strategies for natural forest management directed at sustainable
production of timber and other forest products and services. These methods have to be
ecologically sound, socially acceptable and economically viable (Foahom & Jonkers, 1992). TCP
consists of fourteen interrelated projects in the fields of ecology, forestry, economy, social
sciences, agronomy and soil science. In 1994, ITTO and CFC decided to co-finance six of these
projects, which together form ITTO project PD 26/92. The 'Office National de Développement
des Forêts' (ONADEF) is the agency responsible towards ITTO and CFC for the implementation
of the Project PD 26/92.
The implementing agencies involved in the present study are the Winand Staring Centre for
Integrated land, Soil and Water Research (SC-DLO), the 'Institut de la Recherche Agricole pour
le Développement' (IRAD) and Wageningen Agricultural University (WAU).
ACKNOWLEDGEMENTS
The authors wish to thank those who have contributed to the overall land inventory of the TCP
research area. We gratefully acknowledge the assistance of the Cameroonian Ministry of
Environment and Forests, the Tropenbos Foundation, the 'Office National de Développement des
Forêts', the 'Institut de la Recherche Agricole pour le Développement', the International Tropical
Timber Organization, the Common Fund for Commodities, the Winand Staring Centre for
Integrated Land, Soil and Water Research, Wageningen Agricultural University and the
Directorate General for International Cooperation of The Netherlands' Ministry of Foreign
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Affairs.
Moreover, we could not go on without mentioning the following persons for their
undisputed efforts. First of all we like to thank our supervisors Patrick Hommel and Arie van
Kekem of SC-DLO for their support, encouragement and valuable comments in the different
stages of the project.
Messrs. Wim van Driel, Oscar Eyog Matig, Bernard Foahom, Wyb Jonkers and Jean-Paul
Mendouga Tsimi of the TCP management team are acknowledged for their administrative,
logistic and scientific support.
Maurice Elad, Joseph Ohandza Minkoulou, Dieudonné `Clindor' Ndoum, Prospère Mefane
and Benjamin Nkolo formed the field crew without whom these pages would have been
empty. We are greatly indebted to Tom Bakkum and Arnold Bregt (SC-DLO) for
successfully initiating the GIS in Kribi. Ms. A. Stoffers is specially mentioned for surveying
the northern part of the area. `Our' students Albert Abana, Bernard Tionjock, Martijn van
Gilst, Nienke van Berkum and Fokke de Jong have helped to advance the project in many
ways. All TCP researchers, technicians, drivers and administrative personnel are thanked for
their cordial collaboration. Martin Zogo should be mentioned twice for dealing with all
administrative problems that would have kept us busy for years.
The National Herbarium of Cameroon (Dr. Onana, Dr. Achoungdong, Dr. Sonké Asongonyi
and Mr. Mezili), the Limbé Botanic Garden (Mr. Peguy Mbatchou), the Department of Plant
Taxonomy of the Wageningen Agricultural University (Dr. Breteler and Dr. Jongkind) and
Dr. Duncan Thomas have helped with plant species identification. Mr. Tchuenteu of the
IRAD Ekona soil laboratory has conducted the majority of soil analyses. Mr. van Reeuwijk
of the International Soil Reference and Information Centre (ISRIC) carried out the clay
mineralogy and reference analyses.
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SUMMARY
This report presents the results of the reconnaissance scale landscape ecological survey of the
Tropenbos-Cameroon Programme (TCP) research area in Southwest Cameroon conducted by the
Forest Land Inventory and Land Evaluation project (Lu1). The main objective of the Lu1 project
is to provide a scientific framework for sustainable land use planning in the TCP research area.
Moreover, the Lu1 project provides a basis for all ecologically oriented research activities within
the TCP area and allows for the extrapolation of the research results from sample areas to larger
areas in South Cameroon.
In its first phase a survey of landforms, soils and vegetation is conducted at scale 1 : 100 000 of
the Bipindi - Akom II - Lolodorf region (167 000 ha). Some 250 soil augerings, 45 soil pits and
125 vegetation relevés have been described, covering the most important landscapes. The results
of the analysis of landform, soil and vegetation data are presented in this report and on the
landscape ecological map. The second phase of the project entails the development of a land
evaluation methodology for tropical moist forests in South Cameroon.
Landforms discerned in the TCP research area are mountains, complexes of hills, isolated hills,
hilly and rolling uplands, dissected erosional plains, and floodplains. They are classified on basis
of slope steepness, slope length, relief intensity and number of interfluves. The mountains,
complexes of hills and isolated hills have very steep slopes and high relief intensities, whereas
both the uplands and the dissected erosional plains have gentle to moderately steep slopes and
low relief intensities. The first landform group is therefore more vulnerable to erosion than the
latter.
The following four soil types are dominating in the research area:
– well drained very clayey soils: Nyangong soils;
– well drained clayey soils: the Ebom soils;
– moderately well to well drained sandy loam to sandy clay soils: the Ebimimbang soils;
– very poorly to poorly drained soils: the Valley Bottom soils.
The Nyangong and Ebom soils are deeply weathered yellowish brown to strong brown tropical
clay soils, low in weatherable minerals and with cation exchange capacities in the (ferralic) B-
horizons of less than 16 me/100 g clay. Their dominant clay minerals are kaolinite. The
Nyangong soils have 50-80% clay in the subsoils; the Ebom soils are less heavy with 35-60%
clay. Moreover, topsoils of the latter are lighter (20-50% clay) than the subsoils. The Nyangong
soils classify as Xanthic Ferralsols, the Ebom soils as Acri-xanthic Ferralsols. The Ebimimbang
soils are moderately deep to very deep, yellowish brown, sandy clay loams to sandy clays with
lighter textured topsoils. They are classified as Plinthudults and typic Paleudults. The very poorly
to poorly drained soils are developed in unconsolidated, stratified, recent alluvium. They are
characterized by high groundwater tables, periodic flooding and locally greyish colours. In the
FAO-Unesco classification they are classified as Dystric Fluvisols and Gleyic Cambisols.
All soils in the TCP research area have low pHs and are chemically poor. Their physical
characteristics are good. Removal of the forest vegetation, e.g. by intensive logging or
agriculture, will result in the physical degradation of the soil (decrease in organic matter) and the
loss of nutrients stored in the forest vegetation.
Seven distinct `plant communities' have been identified using a phytosociological approach;
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the analysis of plot data was carried out with the computer programme TWINSPAN. All
vegetation types are defined by floristic composition and the (external) foliage coverage of the
species. Interpretation of successional status, overall physiognomy and general site descriptors
reveals a strong correlation of the plant communities with altitude and disturbance. The
communities discerned are: submontane forest (altitude > 700 m asl), three types of lowland
evergreen forest (< 350 m asl; 350-500 m asl; 500-700 m asl), swamp forest, young secondary
forest and thicket on recently abandoned agricultural fields.
The legend of the 1 : 100 000 landscape ecological map is based on altitude, landform, soil
and vegetation, and has a hierarchical structure. A total of 14 main mapping units has been
discerned. These 14 units have been further subdivided according to vegetation characteristics
brought about by human influences (shifting cultivation) into 34 units. The landscape
ecological map presents the landscape in its complexity of landforms, soils and vegetation.
Cross reference of the inventory data reveals a strong relationship between vegetation, altitude
and soils. This supports the notion that natural vegetation can be seen as a response variable to
environmental factors such as climate and soil. Since vegetation proves to be correlated with
altitude, which is assumed to be related to climatic factors, the latter has been taken as the
highest entry of the map legend. On this basis, the TCP research area is divided into five
ecological zones (A - E).
The overall orientation of the ecological zones is NNE-SSW and follows the general
orientation of the geological structures in Southwest Cameroon. The landscape of the TCP
research area changes considerably from west to east. Altitude rises from approximately 40 to
over 1000 m asl. Dissected erosional plains, hilly and rolling uplands dominate the western
part of the area whereas complexes of hills and mountains are found solely in the east. Going
from west to east the soils change from Ebimimbang to Ebom and Nyangong thereby
increasing in clay content. Valley bottoms are found throughout the area but are more frequent
and wider in the west. The natural vegetation changes from low altitude evergreen forest with
many littoral species to a submontane vegetation with characteristics of cloud forest. Human
activities have influenced this gradient by logging and shifting cultivation. Along the main
access roads and in the vicinity of villages mosaics are found of actual fields, thickets on
recently abandoned fields, young secondary forest and residual patches of tropical moist
forest.
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1 INTRODUCTION
1.1 FOREST LAND INVENTORY AND LAND EVALUATION PROJECT (LU1)
The Tropenbos Cameroon Programme (TCP) coordinates fourteen interrelated projects in the
fields of ecology, forestry, economy, social sciences, agronomy and soil science. This report
presents the results of the reconnaissance scale land inventory carried out in the first phase of the
research project Lu1, titled `Forest Land Inventory and Land Evaluation' (Lu1).
1.2 RESEARCH OBJECTIVES
Detailed and up-to-date information on the abiotic and biotic environment of the TCP research
area is a prerequisite for the formulation of a management plan. This information, however, is
either non-existent (e.g. hydrology and erosion aspects) or not detailed enough for the present
needs (e.g. climate, landforms, soils, land use, vegetation, and wildlife). The Lu1 project is aimed
at filling those gaps which is essential for sound land use planning.
The general objective of Lu1 is to provide a scientific framework for sustainable land use
planning for the TCP research area. This will be realized through the development of a land
evaluation methodology for tropical moist forests. Moreover, the Lu1 project provides a basis for
all ecologically oriented research activities within the TCP and permits the extrapolation of the
results of TCP research to other areas in South Cameroon.
The first phase of the Lu1 project entails an integrated reconnaissance scale (1 : 100 000) survey
on landforms, soils and vegetation. The present report is the result of this integrated survey,
delimitating and describing the major landscape ecological units of the TCP area. In the second
phase of the Lu1 project a qualitative ecological land evaluation will be conducted, investigating
the suitability of each of the landscape ecological units for a number of relevant land-uses.
1.3 COURSE OF THE STUDY
Preliminary work on the interpretation of aerial photographs, including a five-week mission to
the study area, was carried out by Mr. Luc Touber of the DLO- Winand Staring Centre for
Integrated Land, Soil and Water Research (SC-DLO) (Touber 1993a; 1993b).
The Directorate General for International Cooperation of The Netherlands' Ministry of Foreign
Affairs (DGIS) contracted two associate experts for the Lu1 project. Mr. G.W. Hazeu, soil
scientist, started his work in Cameroon in March 1995. His contract expired in September 1997.
In March 1995, DGIS appointed Mr. Barend S. van Gemerden as vegetation surveyor whose
contract expired in December 1997.
The fieldwork for the landform, soil and vegetation survey was carried out between March 1995
and May 1996. Ms. A. Stoffels carried out the field survey of the northern part in the period
April-October 1997.
Overall supervision of the Lu1 project was provided by senior soil and vegetation experts of SC-
DLO. Additional assistance was given by a senior GIS expert of the same institute. A total of
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2 STUDY AREA
2.1 LOCATION AND INFRASTRUCTURE
The TCP research area is situated in Southwest Cameroon at approximately 80 km East of Kribi,
between 2
°47_-3°14_ N 10°24_-10°51_ E. The area is delimitated by the villages of Bipindi,
Akom II and Lolodorf (Fig. 1.1). From an administrative point of view the TCP research area is
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