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

The described land and soil related attributes are based on Touber et al. (1989), FAO (1990) and
Touber et et al. (1993), and include: altitude, slope length, slope steepness, slope form, exposition,
landform, stone and rock coverage, erosion and stability characteristics, drainage drainage characteristics,
groundwater groundwater level, biological activity and, humus form. Soil characteristics, described per horizon,
are: colour, mottling, texture, structure, consistency, cutans, rooting characteristics and pores.
Additionally, schematic sketches of the the transects were made, showing the variation in slope
percentage, slope direction, slope length, and exposition within within each each land unit.
At least three auger hole observations per per transect were made. The auger holes were made with a
standard standard type Edelman auger and and range in depth from 1.2 to 2.0 m. A total of of 207 soil and and landform
observations were made. In Fig. Fig. 3.1 the distribution of observation points in the TCP area is
presented.
After a first survey of the transects, about 60 sites representing the different different landforms and and soil
types of the TCP area were selected, soil pits were dug and soil characteristics were described in
more detail. All soil pits have a minimum depth of 1.50 m. Samples of horizons were collected for
chemical and physical analysis.
Soil samples were chemically and physically analyzed at the IRA soil laboratory in Ekona.
Duplicates of some 40 samples were analyzed as control at ISRIC, Wageningen. Chemical soil
properties properties determined are organic carbon, total nitrogen, available and total phosphorous, pH H H20 20
and KCI, exchangeable exchangeable bases (Na, K, Mg and Ca), Ca), aluminum aluminum and hydrogen, and cation exchange
capacity capacity (CEC). Physical Physical parameters determined are are texture, water retention characteristics (pF)
and bulk density. Additionally, the clay mineralogy of of some twenty-five samples were analyzed
by ISRIC. The methods used for chemical and physical physical analyses analyses are described in in Annex IV.
All field data concerning the site and soil characteristics of of the augerings augerings and and soil soil profile
descriptions were compiled compiled in in the the TROFOLIN Database Database (Touber et al., 1993). Data of chemical
and physical analysis are stored stored in QUATTRO QUATTRO PRO.
3.3.3 Vegetation
The distribution of plant species in tropical forests is not random but reflects environmental
conditions (Whitmore, 1984 and Zonneveld, 1995). Species which can successfully compete with
one another another within the limits of a a particular combination of of environmental features can be be
considered as a plant community. The mosaic of plant communities forms the vegetation in an area
(Kuchler and Zonneveld, 1988). Moreover, the pattern of of vegetation vegetation types, defined defined as plantcommunities,
may be used to assess the distribution patterns of distinct plant species.
In the present survey the vegetation was described on the basis of its structure and floristic
composition, in the sense of the the French-Swiss school (phytosociological (phytosociological approach; approach; Braun­ Braun­
Blanquet, 1964). The method implies a classification of vegetation vegetation types by tabular tabular comparison
of plot plot data, which leads leads to to the identification identification of communities, characterized by phytosociological
groups (Touber et at., 1989).
The localities described in the vegetation survey lie within the most common and widespread widespread photo
interpretation units in the TCP research area (see 3.3.1). The stratification of sample points is based
on the hypothesis that altitude (Fig. 2.1) and disturbance disturbance (both anthropogenic and and natural) cause
most of the variation in the vegetation in the TCP research area. The observation points are are
therefore evenly spread along these two environmental gradients gradients (Table 3.1). Additionally, Additionally, in in
relatively relatively undisturbed forest vegetation efforts have have been been made to to describe describe the the vegetation vegetation along along
the toposequence, comparable to the study of catena's in the soil survey.
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