[en] Landscape Ecological Survey of the Bipindi-Akom II ... - ITTO

The combination of block faulting and the process of denudation (mechanical (mechanical and and chemical
erosion) have resulted in planation or erosion levels of different age, which might be the the
explanation for the differences differences encountered in the landforms and soils in the TCP research area.
The eastern eastern region of the TCP region has been lifted upwards in relation relation to to the western lowlands lowlands
along NE-SW orientated faults. The denudation, denudation, which can be be called (valley floor)
pedimentation (Zonneveld, 1981; Embrechts and Dapper, 1987), has resulted in almost flat
erosional plains with inselbergs in the the western lowlands and in a very very dissected landscape in the the
mountainous eastern region. This dissected dissected landscape has been developed originally from an old
erosional plain. The progressive erosion (slope retreat) from West to East has resulted in very
small differences in altitude (Iow relief intensity) intensity) between the western part of the TCP research
area and and the Atlantic Ocean, i.e. the the erosion basis. It is concluded that the landscape in the the
western part of the TCP research area area is younger than than the the eastern one.
The soil forming processes, which are mentioned in section 5.5.2., may have been causing
spatial variations. A downward trend from West to East in rainfall and temperature may have
caused differences in intensity and nature of the soil forming forming processes. This trend, however,
is locally disturbed by the topography. Lower amounts of rain are observed around Bipindi
(Waterloo et al., 1997) and can be an additional explanation for richer and less deep soils in
these western lowlands.
Additionally, the age of the landscapes within the TCP research area varies and as a result, the
soil forming processes differ in their periods of activity. Hydrolysis in the western lowlands is
not in as advanced state as in the eastern region. Moreover, the importance of soil forming
processes processes such as plinthite formation and clay illuviation decreases from West to East. Besides
the variation in rainfall and temperature and the different ages of the landscapes in the research
area, the spatial distribution of the soil forming processes is also influenced by topographical
position. All these factors result in in differences in soil drainage, drainage, texture and soil depth. depth.
The soils are relatively uniform in colour but differ differ in texture, depth or drainage. The variation
in texture seems to be related to to differences in the age of the landscape. Perhaps small, during
the the survey not noticed, differences in texture and mineralogical composition of parent material
could also be important. Younger areas like the western lowlands have less weathered soils,
resulting in coarser textured textured soils (Ebimimbang soils), soils), whereas whereas the deeply weathered soils in the
eastern region region have a predominant predominant clayey clayey texture. The less weathered soils are richer in in
nutrients, have higher pHs and clear clay cutans (evidence of active clay clay movement to the
subsoils) and are less deep deep than than the the clayey textured textured Nyangong soils formed in an older
landscape.
Drainage differences are especially related to topographical positions. The valleys have poorly
to very poorly drained soils, whereas on the other topographical positions, moderately well to
well drained soils occur.
The variability in soil depth may be large at small distances for which relative resistance to
weathering of the the parent rock and the the degree of fracturing may may be an explanation.
Further research (e.g. clay mineralogy, geomorphological processes, geology) is needed to
elaborate these theories. theories. Also, research on the variation of soil depth with topographic topographic position
(catena) (catena) will will be very useful for a better understanding of processes which are active in the TCP
research area.
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