Geology Reference
In-Depth Information
Pachystela msolo
could have qualified as a North-
en species but it seems so widespread elsewhere,
and so rare in the coast, that this status probably
reflects insufficient sampling. For similar reasons
Cnestis coniculata
(previously
. conertlora)
does
not quite qualify as a Southern species, in spite of
not having been recorded in the Northern forests.
Membership of a geographical element takes
precedence over membership of an ecological ele-
ment. The three ecological elements are the Dry
orest, Moist forest and Mariime-Riverine ele-
ments. Species in the ecological elements occur
north and south of the Msangasi River.
categories are not confined to swamps, river banks
and similarly extreme habitats. Their general
preference for such habitats throughout the coast
and beyond, however, points to some niche
specialisaion that disinguishes them rom spe-
cies in the other ecological elements. Many spe-
cies in the Maritime-Riverine element, e.g.
Parkia filicoidea,
are widespread outside the
Zanzibar-Inhambane regional mosaic along
rivers, but often in a wide range of other vegeta-
tion types (see Hopkins & White, 1984).
Figure 5.4 shows the representaion of dif-
ferent elements in some coastal forest samples.
These 'ecogeographic spectra' indicate the rela-
ive importance of the various ecogeographic
categories within samples of coastal forest. Sam-
ples were plotless, and defined by posiion in the
landscape. For instance, samples might be of all
species recorded in forest along a particular river
or stream, or all species on a certain north-facing
slope. Most samples include 40 or more species.
Within these samples, all species were scored 1-3
depending on their abundance (most scored 1).
Each species' score is expressed as a percentage
of the total for all species in the sample, then the
scores are added for all species in each ecogeo-
graphic category.
The variaion in these spectra over many sam-
ples of coastal forest expresses in a simplified and
meaningful way the same patterns that are
revealed by mulivariate analyses, for instance
Detrended Correspondence Analysis (Haw-
thorne, 1984). Analysis of a sample of forests
(unfortunately without comparable samples from
the south Kenyan coast) showed that variaion
along a north-south ais is most significant, with
subsidiary variaion according to posiion in
landscape.
Further details on the various ecogeographical
elements will be given after a summary of forest
ypes.
Ecological elemens
The definition of ecological elements goes hand
in hand with deiniion of forest types. Species in
the Moist forest element (labelled M in Appendix
5
.1) are restricted to areas where the forest, if
undisturbed, is of a Moist type. More specialised
Moist forest species that occur in higher altitude
or higher rainfall areas are distinguished in a
separate category (MH).
Species of the Dry forest element (D) are
characterisic of a wide range of Dry forest types
but some are also common in Moist forest, or in
thickets or woodland. This element is therefore
well represented in all coastal forests.
Mariime-Riverine species favour, within the
coast at least, riversides, rocky, saline or base-rich
soils, termite hills or other edaphically more
extreme sites. Most Mariime-Riverine species
favour various combinaions of such habitats.
Many categories of the Mariime-Riverine ele-
ment could be defined (Hawthorne, 1984), but
here they are simplified to just three:
l.
Mariime-Riverine species also
characterisic of various types of Moist
forest (LM in Appendix 5.1);
2.
Maritime-Riverine species that occur
often in Dry forest (LO);
3. the remainder, which are more specialised
and found mostly on stream banks or in
very rocky areas (LR).
Ty pes of forest
In the classificaions of Kenyan coastal orests by
Dale (1939) and Moomaw (1960) large areas of
forest are defined under one forest type, despite
great variaion over short distances. Informal,
It should be emphasised that, within the coastal
orests, species in the first two Mariime-Riverine
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