MEDICINAL PLANTS DIVERSITY, USES AND ECOLOGICAL
FACTORS THAT INFLUENCE THEIR DISTRIBUTION IN THE SANGO
BAY AREA, SOUTHERN UGANDA
A lady puts tree bark material in saucepan for preparation. The decoction of the bark
of Hallea rubrostipulata (K. Schum.) J-F Leroy is used in the treatment of malaria.
By
Paul Ssegawa
B.Sc. For. (Mak), M.Sc. Env. (Mak)
A thesis submitted to the School of Graduate Studies for the award of
the degree of Doctor of Philosophy of Makerere University
July 2007
ABSTRACT
This study was conducted from October 2002 to August 2004 in the Sango
bay area, southern Uganda. This study focussed on the medicinal plant
species used by the communities surrounding the Sango bay forest reserves
with emphasis on herbal medicine used in malaria treatment. The aim was to
explore the medicinal plant diversity, uses, preferences and ecological viability
of the popular medicinal plants. This study also explored the diversity of
woody plants and factors influencing their diversity and distribution in the
forest reserves.
Ethnobotanical information on wild plants was collected through interviewing
205 respondents from 72 households. These were from the thirteen villages in
the three subcounties surrounding the forest reserve. Household respondents
were chosen through stratified random sampling whereby a household was
picked randomly as we walked along paths in each of the villages with the
assistants. A structured questionnaire was used to collect data on local plants
names, uses, parts used, and modes of preparation and administration.
Special emphasis was placed on the local plants used to treat malaria
because of its high prevalence, poverty and inadequate primary health care
facilities in the area.
Floristic data were collected using the transect and quadrat method. The
transects and plots were located throughout the Malabigambo and Kaiso
forests. Small plots of 0.1 ha. were used to census trees  5 cm dbh. In total,
forty-five plots covering 4.5 ha. were sampled. Forty-five random soil core (8
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cm diameter x 15 cm deep) samples were collected in the 45 sample plots.
The samples were air-dried and sieved using a two mm sieve. These were
analysed for sand, silt, clay, P, K, Na, Ca, Mg, organic matter and pH. Other
parameters measured included canopy cover and height.
The floristic assessment of the forests yielded 2421 individual trees belonging
to 140 species in 108 genera and 42 families. These also produced a
combined basal area of 167.32 m 2. A total of 21 families were represented by
one species each, and the others were represented by 2 – 18 species each.
The family Moraceae had the highest number of species followed by
Euphorbiaceae and Rubiaceae. The most species rich genus was Ficus with
15 species. Out of the 140 species, seven (5%) occurred in over 30 plots, 38
(27.1%) occurred in over 10 plots and 38 (27.1%) occurred in one plot only.
The first two canonical correspondence analysis (CCA) axes accounted
respectively for 28.8% (eigenvalue = 0.489) and 23.9% (eigenvalue = 0.406)
of the extracted variance in the species-environment relationship, and for
14.6% and 12% of the inertia of species data. Therefore, the first two
canonical axes explained about 52.7% of the species-environmental
relationships and 26.6% of the variation in species assemblages. The forward
selection procedure of environmental variables by CANOCO showed that
canopy cover explained the most variance (0.39). Canopy cover contributed
significantly (at 5% level) to the model of already included variables. Canopy
cover influences the regeneration of species especially in the lower forest
strata by controlling the amount of light reaching the lower forest strata. In the
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present study, the ordination of species and environmental variables shows
that the factors measured are probably only part of a complex of factors that
influence plant species diversity and distribution since the measured
environmental variables could only explain 52.7% of the variance in the
species-environment relationship. The unexplained variation is probably due
to other relevant environmental factors that were not taken into account in this
study such as the flooding regime.
A total of 187 medicinal plants species, belonging to 163 genera and 58 plant
families was observed. The largest proportion of medicinal plant species
belong to the families Fabaceae (16%), Asteraceae (14.4%), Euphorbiaceae
(7.5%) and Lamiaceae (5.9%) in decreasing order of frequency of reported
use. Herbs were the main source of medicinal plants in terms of number of
species (51.3% of total species) followed by trees and shrubs. The plant parts
used for medical preparations were leaves, shoots, roots, bark, twigs, sap,
bulbs, flowers, seeds, internodes, and fruits. In some cases the entire plant is
utilised including the roots. The most frequently utilised plant part was the
leaves (48.7%) followed by the shoots (18.2%) and roots (12.3%). Gastrointestinal problems, psycho-spiritual problems were among the most frequent
ailments treated with the medicinal plants registering 23.5% of the total
ailments reported.
Sixteen plant species belonging to 11 families and 14 genera were reportedly
used to treat malaria. Four species belonged to the family Fabaceae.
Asteraceae and Myrtaceae were represented by two species each whereas
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the other families were represented by a single species each. Eight species
(50%) were trees, two (12.5%) were shrubs and six (37.5%) were herbaceous
plants. Eight (50%) of the species recorded were typical forest species
whereas the others also occur in grassland and other vegetation types. The
most important species used was Hallea rubrostipulata (tree) ranked by 51
(63.8%) of the respondents followed by Vernonia amygdalina (shrub),
Warburgia ugandensis (tree) and Syzygium guineense (tree) being ranked by
40%, 28.8% and 16.3% of the respondents, respectively. Hyptis pectinata,
Indigofera congesta, Manilkara obovata and Sopubia ramosa were reported
for the first time as plants that can be used to treat malaria according to
Ugandan published literature on medicinal plants.
The communities of the Sango bay area have a relatively high diversity of
medicinal plants they use in primary health care. Many of the plants in this
inventory have not been recorded before for the medicinal uses recorded
here. Significant patterns of medicinal plant use are that people use a wide
range of medicinal plants to treat many ailments; many of these plants are
harvested from the wild and few are protected in home gardens; and that
there is limited initiative at a local level to ensure a continued availability of
medicinal plants.
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