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to be established. Vegetation types were classified according to concepts of Greenway
(1973) and White (1983), Herlocker (1999) and Beentje (1994). This classification
combines physiognomic and floristic criterion including the dominant species in the
community.
The vegetation communities were sampled from 26 plots each measuring 20x50m
along six transects, at an interval of 50m apart in the beginning to100m interval later.
The transects were randomly selected. Nested Quadrant Method (Stohlgren et al. 1995
and Crawley 1997) was employed to sample trees, shrubs, lianas and herbs as
indicated below:
Life form Fixed plot area Length Width Definition
Herbs 1.0m 2 2.0m 0.5m All herbs, grasses, sedges under 1.5m
tall
Shrubs, lianas 10.0m 2 5.0m 2.0m Woody plants >1.5m with dbh 5.0m and dbh >10cm
The mangrove formations, the fragmented Albizia-Erythrophloeum forest remnants
and the Erica bushland (heathland) were not quantitatively sampled, but their species
compositions were identified and recorded wherever they were considered to be new
to the check-list. The species from fresh water swamps and ponds were also recorded
but not quantitatively sampled.
Sampling in the nested subplots from the main plots involved counting and recording
the herbs and shrubs of all individual species. All trees in the 50mx20m plot were
recorded and their dbh measured together with their heights. Individual tree numbers
in study plots provided basic information for calculating species abundance, basal
area per ha. -1 and ranges for dbh and heights. The distribution of diameters (dbh) and
heights of tree species using classes of the respective attributes are provided in the
results. Other attributes include density (stems/ha -1 and basal area (m 2 ha - ). The
calculations show the demographic status of species over different communities.
3.2 Vegertation mapping
3.2.1 Interpretation and field verification
The main sources of information were aerial photographs at the scale of 1:10,000 and
in some cases 1:50,000. The first stage was interpretation where major topographic
features and the preliminary vegetation types were identified. The second stage
involved final interpretation after field verification. Interpretations were made on
transparent films. GPS readings were taken in different areas with their corresponding
vegetation types. All vegetation types previously identified were covered.
3.2.2 Digitization and rectifications
The transparent films obtained from the thematic interpretation of different vegetation
types were digitized using ArcInfo software. Further manipulation of digitally
captured datasets e.g. area statement computation was done using ArcInfo, ArcView,
and Microsoft Excel.
All digitized data sets underwent the following processes:
♦ Creation of raw digitized coverage
♦ Cleaning of the coverage (identifying errors)
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