Open Journal of Forestry
2013. Vol.3, No.4, 138-151
Published Online October 2013 in SciRes (
Copyright © 2013 SciRes.
Diversity, Population Structure and Regeneration Status of
Woody Species in Dry Woodlands Adjacent to
Molapo Farms in Northern Botswana
John Neelo1, Demel Teketay2*, Wellington Masamba1, Keotshephile Kashe1
1Okavango Research Institute, University of Botswana, Maun, Botswana
2Department of Crop Science and Production, Botswana College of Agriculture, Gaborone, Botswana
Email: *, *
Received July 27th, 2013; revised August 30th, 2013; accepted September 12th, 2013
Copyright © 2013 John Neelo et al. This is an open access article distributed under the Creative Commons At-
tribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the
original work is properly cited.
The diversity, population structure and regeneration status of woody species were studied at Xobe and
Shorobe Villages in northern Botswana. A total of 130 and 111 quadrats of 20 × 20 m size were laid
down at 50 m intervals along parallel line transects at Xobe and Shorobe, respectively. A total of 46
woody species, 27 from Xobe and 41 from Shorobe were recorded. Of the 46 woody species, only 22
were recorded at both sites. Ten genera and six families were found only in Shorobe while one genus and
one family were found only in Xobe. The diversity and evenness of woody species were 1.5 and 0.5 in
Xobe, respectively, and 2.18 and 0.6 in Shorobe, respectively. The similarities of woody species in terms
of richness of species, genera and families at the two sites were about 50%, 54% and 56%, respectively.
The mean densities of woody species were 2745.7 ± 1.35 and 4269.7 ± 36 individuals ha1 at Xobe and
Shorobe, respectively. Despite differences in absolute numbers, the total mean densities of woody species
at both sites did not exhibit significant (P = 0.35) differences. At both sites, woody species were
dominated by individuals of only a few species, which also exhibited the highest values of important
value index. The population structure patterns of the woody species were categorized into five groups.
The species in the first group exhibited reverse J-shaped distribution, which indicates stable population
structures. The species in the second group showed relatively good recruitment but the regeneration is
negatively affected. The species in the other three groups exhibited hampered regeneration as a result of
disturbances caused by humans, domestic animals and annual fires. The parameters assessed indicate the
need for attention and appropriate management interventions by the relevant national authorities at vari-
ous levels.
Keywords: Density; Dominance; Floristic Similarity; Frequency; Grazing; Important Value Index;
Species Richness
Dry forests and woodlands, including those in Botswana,
form more than 40% of all tropical forests, and Africa and
tropical islands of the world house the largest proportion of dry
forest and woodland ecosystems where they account for 70% -
80% of the forested area (Murphy & Lugo, 1986). Tropical dry
forests and woodlands have been under exploitation for thou-
sands of years since they have often been preferred for human
settlement to wetter forest zones for biological and ecological
reasons (Murphy & Lugo, 1986; Janzen, 1988). As a result,
they are either vanishing or being degraded rapidly due to ac-
celerated growth of human and livestock populations, which
result in the conversion of forested land to agriculture and ex-
cessive exploitation of forests for fuelwood, construction ma-
terial and timber for export. For instance, of all the harvested
wood in the tropics, 80% is used for fuel purposes, and the
proportion is higher (90%) in the African tropics, where dry
forests are predominant (Murphy & Lugo, 1986). A typical
example is Kenya, which obtains 74% of its energy require-
ments from wood (Lamprecht, 1989).
Janzen (1988) has also argued that the threat to the tropical
dry forests is multiple as well as complex, and tropical dry for-
ests are the most threatened of the major tropical forest types,
emphasising the urgent need for studying, conserving and re-
storing tropical dry forest ecosystems. The loss or degradation
of forests results in land degradation in the form of soil erosion
and decline of fertility, decline or loss of biodiversity and water
bodies, impoverishment of ecosystems and global warming,
which affect the welfare of humans, plants, animals and mi-
cro-organisms negatively (Teketay, 2004-2005).
The challenge generated by the reduction and degradation of
forest cover can be adequately met only if serious efforts are
made, on the one hand, to maintain the remaining forests and
on the other to restore deforested and degraded areas (Teketay,
1996a). This requires understanding of the diversity and natural
dynamics of woody species, i.e. causes, mechanisms and fac-
*Corresponding author.
tors that drive the process of regeneration of woody species as
well as population change and replacement through time (Go-
mez-Pompa et al., 1991; Teketay, 1996a).
Therefore, studies on population structure and density of
major canopy tree species can help to understand the status of
regeneration of species, and, thereof, management history and
ecology of the forest or woodland (Harper, 1977; Lykke, 1998;
Sano, 1997; Teketay, 2005a, 2005b; Mwavu & Witkowski,
2008, 2009a, 2009b; Tesfaye et al., 2010). Plant population
structure shows whether or not the population has a stable dis-
tribution that allows continuous regeneration to take place (Rao
et al., 1990; Teketay, 1997a; Tesfaye et al., 2002; Mwavu &
Witkowski, 2008, 2009a, 2009b; Tesfaye et al., 2010). If re-
generation was taking place continuously, then, the distribution
of species cohorts would show reverse J-shaped curve, which is
an indicator of stable regeneration (Harper, 1977; Teketay,
1997a, 2005a, 2005b; Mwavu & Witkowski, 2009b). Hence,
analyses of population structures, using frequency distribution
of diameter classes of naturally regenerated woody species, can
provide an insight into their regeneration status (Sano, 1997;
Lykke, 1998; West et al., 2000; Obiri et al., 2002; McLaren et
al., 2005; Mwavu & Witkowski, 2008, 2009b), which plays a
key role in the promotion of their sustainable management,
utilization and conservation.
Several studies in Benin (Sokpon & Biaou, 2002), Burkina
Faso (Savadogo et al., 2007; Zida et al., 2007; Pare et al., 2009;
Bognounou et al., 2010; Sop et al., 2011), Ethiopia (Teketay,
1997a; 2005a, 2005b; Tesfaye et al., 2010; Teketay, 2011;
Fiseha et al., 2013), Ghana (Swaine et al., 1990), Oman (El-
Sheikh, 2013), South Africa (Shackleton, 1993; Helm & Wit-
kowski, 2012), Tanzania (Luoga et al., 2004), Uganda (Tabuti,
2007; Mwavu & Witkowski, 2008, 2009a, 2009b; Kalema, 2010),
South Africa (Obiri et al., 2002; Venter & Witkowski, 2010;
Helm & Witkowski, 2012) and West Africa (Poorter et al.,
1996) demonstrated the crucial role of natural regeneration in
the sustainable management of forest and woodland resources.
Forest (20%) and woodland (60%) resources cover 80% of
the total land area of Botswana (FAO, 2010). Despite the rela-
tively high forest and woodland cover, research undertakings
on the various attributes of these resources are not adequate.
The research activities carried out so far focused on investiga-
tions on the various attributes of woody species in relation to
elephants and fire (e.g. Ben-Shahar, 1993, 1996a, 1996b, 1998a,
1998b; Ben-Shahar & Macdonald, 2002; Robinson et al., 2002;
Heinl et al., 2004; Rutina, 2004; Makhabu, 2005a, 2005b; Ru-
tina et al., 2005; Makhabu et al., 2006; Heinl et al., 2007; Ram-
part, 2007; Heinl et al., 2008; Tacheba et al., 2009; Kalwij et al.,
2010; Aarrestad et al., 2011; Mmolotsi et al., 2012).
A long-term study has been set up and carried out since 1997
on three pairs of permanent (fenced and unfenced) plots estab-
lished in the Mokolodi Nature Reserve, southeastern Botswana
(Skarpe, 1990a, 1990b, 1992; Käller, 2003; Bengtsson-Sjörs,
2006; Leife, 2010; Aarrestad et al., 2011; Herrera, 2011). These
studies have been monitoring to assess the dynamics of woody
species over time.
Also, although it has never been implemented, an inventory
has been carried out to develop the management plan of Chobe
Forests in 1993 (NFS, 1993). Other studies have also been con-
ducted focusing on different aspects of the vegetation resources
in northern Botswana (Ringrose et al., 1998; Ringrose et al.,
1999; Bonyongo et al., 2000; Sekhwela et al., 2000; Sekhwela,
2003; Barnes, 2001; Moleele et al., 2001; Ringrose & Mathe-
son, 2001; Moleele et al., 2002; Mosugelo et al., 2002; Rin-
grose et al., 2002; Ringrose, 2003; Neudeck et al., 2012; Babit-
seng & Teketay, 2013).
However, knowledge about diversity, population structure
and natural regeneration of woody species is still scanty or
lacking in Botswana. Particularly, no studies have been under-
taken on these themes in areas where flood recession (locally
known as molapo, plural melapo) farming (Oosterbaan et al.,
1986; Bendsen, 2002; Vanderpost, 2009; Motsumi et al., 2012)
is practiced by farmers in Ngamiland District, northern Bot-
swana (Figure 1). Molapo farming is mainly practiced in the
Okavango Delta and involves clearing of vegetation from fields
in seasonally flooded areas for agriculture as well as lopping
branches (Figure 2(A)) and cutting trees for fencing farms
(Figure 2(B)) and kraals (Figure 3(A)). The clearing of vege-
tation may affect the diversity, population structure and natural
regeneration of woody species as well as predispose the areas to
The specific objectives of the study were to: 1) investigate
the species richness, diversity and evenness of woody species; 2)
assess similarities in composition of woody species between the
two study sites; 3) determine the density, frequency and domin-
Figure 1.
Molapo farms, partly flooded (A) (VanderPost, 2009) and an example
of a molapo farm with maize ((B), picture taken by Demel Teketay), in
the Okavango Delta, northern Botswana.
Figure 2.
Molapo farms cleared and fenced with lopped branches (A) and stems
(B) cut from woody species growing naturally at Xobe (pictures taken
by Demel Teketay).
Figure 3.
Woody plants cut and used for constructing kraals (A) and large areas
cleared of woody vegetation for dryland rain-fed agriculture (B) at
Xobe (pictures taken by Demel Teketay).
Copyright © 2013 SciRes. 139
ance and important value indices of woody species in the study
sites; and (iv) assess the population structure and regeneration
status of woody species in the study sites.
Study Sites
The study was carried out in Xobe and Shorobe Villages, lo-
cated in the Ngamiland District, northern Botswana (Figure
4(a)). The two villages have been identified as suitable sites
since they have different flooding patterns (Figure 4(b)) and
local topography and, consequently, variations in mola po
farming practices (Chimbari et al., 2009). The two villages fall
within the Okavango Delta, part of the wetland system, which
starts in the highlands of Angola. The molapo farming system
in these areas is dependent upon the rainfall at the source aver-
aging 1400 mm per year with the Okavango Delta receiving an
Figure 4.
Map showing study sites ((a), Chimbari et al., 2009) and the main mo-
lapo farming areas in the Okavango Delta ((b), VanderPost, 2009),
average of 450 - 5
northern Botswana.
00 mm per year (McCarthy et al., 1998). The
ion of 418 (CSO, 2011) people,
ee molapo fields (replicates), at least
total area of 4.44 ha
parameters were re-
vegetation in Shorobe and Xobe is dominated by mopane
[Colophospermum mopane (J. Kirk ex Benth.) J. Kirk ex Leo-
nard] and mixed species of Acacia, respectively (DEA, 2008).
Shorobe Village is located in Ngamiland East Sub-District
out 36 km northeast of Maun. It lies between 19˚45'56.71''
latitude and 23˚40'10.53'' longitude and has a population of
1031 (CSO, 2011). To the northwest of the village, there is an
extensive network of molapo fields fed by the Santantadibe and
Gomoti Rivers and by backflow from the Thamalakane River.
Soils in molapo fields are classified as young alluvial soils.
Texture varies from clayey (35% to 60% clay), especially in
low-lying areas, through fine loamy (18% to 35% clay) to
coarse loamy (<18% clay) (Chimbari et al., 2009). Flooding of
most molapo fields has not occurred for several years until
flood waters returned in 2009. When floods occur, molapo
fields are cultivated as the flood recedes. The villagers practise
both arable and pastoral farming. The main crops planted are
maize, sorghum, millets, pumpkins, water melons, melons,
sweet reeds, beans and groundnuts. The local people are also
engaged in traditional beer brewing and palm wine making,
fishing and basket weaving.
Xobe Village, with a populat
a cattlepost area on the south bank of the Boteti River, about
13 km east of Maun. The area lies between 20˚7'10.26' latitude
and 23˚27'41.26'' longitude. The river normally floods in July,
but in dry years (e.g. in the late 1990s), the flood may not reach
the settlement. Soils in Xobe settlement molapo fields are
coarse textured alluvial deposits (Chimbari et al., 2009). Live-
lihood activities for people in Xobe settlement include rain-fed
farming, molapo farming, irrigated vegetable production and
livestock rearing. Molapo farmers cultivate along the river
banks as the water flow recedes. Ploughing is done using don-
keys, though smaller areas may be cultivated with hand hoes.
The main crops planted are maize, pumpkins, sweet sorghum
and gourds. Other activities include harvesting of wild plants
for sale and fishing.
Data Collection
At both study sites, thr
e kilometer apart, and having adjacent vegetation were ran-
domly selected for the study. To assess plant diversity (species
richness and evenness) and density, abundance, frequency,
dominance (basal area), population structure, regeneration
status and important value indices of the woody species, three
one kilometre long (depending on the size of the field) parallel
line transects, 50 meters apart, were used in each molapo field.
Quadrats measuring 20 × 20 m were laid down at every 50
meters interval along the line transects.
A total of 111 quadrats representing a
ere sampled to assess the woody vegetation at Shorobe. Simi-
larly, a total of 130 quadrats representing a total area of 5.2 ha
were sampled to assess the woody vegetation at Xobe. The
number of quadrats in Shorobe were lower than those in Xobe
since one of the sites used for the survey had shorter transects
because of the surrounding settlements.
In each of the quadrats, the following
rded: identity of all woody species (WS), number of live
individuals of all WS and diameter at breast height (DBH) of
all woody species (with DBH >2 cm), except juveniles (seed-
lings and coppices). In the case of seedlings and coppices, the
Copyright © 2013 SciRes.
number of individuals of each species was counted and re-
corded in each quadrat. A calliper and graduated measuring stick
were used to measure diameter, respectively, of the woody plants.
Plant species identification was done first directly in the field
Data Analyses
s (S) is the total number of different woody
woody species was analysed by using the
where, H' = Shannon index, S = species richness, P = propor-
ing relevant manuals and other reference materials as well as
with the help of local people familiar with the flora. Plant no-
menclature in this article follows that of Setshogo and Venter
(2003) and Setshogo (2005).
Species richnes
ecies recorded in each of the project sites. It does not take
into account the proportion and distribution of each species at
the project sites.
The diversity of
annon Diversity Index (H) (also known as the Shannon-
Weiner/Weaver Diversity Index in the ecological literature)
(Krebs, 1989; Magurran, 2004). The index takes into account
the species richness and proportion of each species in all sam-
pled quadrats of each project site. The following formula was
used to analyse woody species diversity:
tion of S made up of the ith species (relative abundance).
Evenness or equitability, a measure of similarityof the
nces of the different woody species in the sampled project
sites, was analysed by using Shannons Evennessor Equitability
Index (E) (Krebs, 1989; Magurran, 2004). Equitability assumes
a value between 0 and 1 with 1 being complete evenness. The
following formula was used to calculate evenness.
where, J' = evenness and S = species richness.
of the two sites
The similarity in woody species composition
as computed by using Jaccard’s Similarity Coefficient (SJ)
(Krebs, 1989). The values of SJ range between 0 and 1: 0 indi-
cates complete dissimilarity and 1 indicates complete simi-
larity in species composition. The following formula was used
to determine similarity of the woody species in the two sites:
S aabc
where, a = number of woody species common in the two sites;
cies was determined
as the proportion (%) of
) indicates the relative eco-
n structure of each woody species in each of the
Species Richness, DiveEvenness
s representing
corded from
y species were 1.5 and
b = number of woody species recorded only in Xobe; and c =
woody species recorded only in Shorobe.
The mean density (MDE) of woody spe
converting the total number of individuals of each woody
species encountered in all the quadrats and all transects of the
three replicated areas in each of the two sites to equivalent
number per hectare as described in Mueller-Dombois and El-
lenberg (1974). Student’s t-test, at the confidence level of P <
0.05 (Zar, 1999), was used to assess if differences existed
between the mean values of total densities of woody species at
Xobe and Shorobe.
The frequency (MF) was calculated
e number of quadrats in which each woody species was re-
corded from the total number of quadrats in each of the sites.
The dominance of the woody species, with diameter at breast
height (DBH) of >2 cm, was determined from the space occu-
pied by a species, usually its basal area (BA). The mean
dominance of each species was computed by converting the
total basal area of each woody species to equivalent basal area
per hectare (Kent & Coker, 1992).
The important value index (IVI
gical importance of a woody species in each of the project
sites (Kent & Coker 1992). It is determined from the summa-
tion of the relative values of density, frequency and dominance
of each woody species. Relative density (RMDE) was calcu-
lated as the percentage of the density of each species divided by
the total stem number of all species ha1. Relative frequency
(RMF) of a species was computed as the ratio of the frequency
of the species to the sum total of the frequency of all species.
Relative dominance (RMDO) was calculated as the percentage
of the total basal area of a species out of the total basal areas of
all species.
o project sites was assessed through histograms constructed
by using the density of individuals of each species (Y-axis)
categorized into ten diameters classes (X-axis) (Peter, 1996), i.e.
1 = <2 cm; 2 = 2 - 5 cm; 3 = 5 - 10 cm; 4 = 10 - 15 cm; 5 = 15 -
20 cm; 6 = 20 - 25 cm; 7 = 25 - 30 cm; 8 = 30 - 35; 9 = 35 - 40;
10 = >40 cm. Then, based on the profile depicted in the popula-
tion structures, the regeneration status of each woody species
was determined.
rsity and
A total of 46 different species of woody plant
families and 24 genera were recorded from the two sites.
Only two species, one species at each site, were not identified.
Of these, 27 (10 families and 14 genera) and 41 (15 Families
and 23 genera) woody species were recorded at Xobe and
Shorobe, respectively (Tables 1 and 2). Fabaceae (Legumino-
sae) was the most diverse family at both Xobe and Shorobe
represented by 12 (about 46%) and 15 (about 38%) woody
species, respectively. The second and third most diverse fami-
lies were Combretaceae [with 4 species (about 15%) at Xobe
and 6 species (15%) at Shorobe] and Tiliaceae [with 3 species
(about 12%) at Xobe and 4 species (10%) at Shorobe], respec-
tively. Capparaceae, Ebenaceae and Rhamnaceae were repre-
sented by two species (5%) each at Shorobe. All other families
contained only one species at both sites. Ten genera and six
families were found only in Shorobe while one genus and one
family were found only in Xobe (Tables 1 and 2).
Of the 24 genera encountered, 14 and 23 were re
obe and Shorobe, respectively. At both sites, Acacia was the
most diverse genus with 8 (about 57%) and 9 (about 39%) spe-
cies of the total number of genera at Xobe and Shorobe sites,
respectively. Combretum and Grewia [with 3 species (about
21%) each] were the second diverse genera followed by
Philoneptera [with 2 species (about 14%)] at Xobe. Similarly,
Combretum and Grewia [with 4 species (about 17%) each]
were the second diverse genera followed by Philoneptera, Al-
bizia and Terminalia [with 2 species (about 9%) each] at
Shorobe. All the other genera were represented only by one
species at both sites (Tables 1 and 2).
The diversity and evenness of wood
5 in Xobe, respectively, and 2.18 and 0.6 in Shorobe, respec-
Copyright © 2013 SciRes. 141
Copyright © 2013 SciRes.
ody species recorded from Xobe with their densities (individuals ha1), frequencies (%), dominance (m2·ha1), relative values (%) of densi-
Species Family Local names MDE MF MDO*RMDE RMF RMDOIVI
Table 1.
List of wo
ties, frequencies and dominance as well as Important Value Index (MDE = mean density, MF = mean frequency, MDO = mean dominance, RMDE =
relative mean density, RMF = relative mean frequency, RMDO = relative mean dominance and IVI = important value index).
Acacia melliferaF Fabaceae Mongana 1194.382.233.4 45.8 19.2 25.2 90.2
Acacia tortilis Fabaceae Mosu 1068.469.949.7 37.5 16.2 36.1 89.8
Philenoptera ne lsii Fabaceae Mohatha 106.1 35.922.2 3.7 8.2 16.1 27.9
Acacia luederitzii Fabaceae Mokgwelekgwele 49.3 28.310.6 1.7 6.5 7.6 15.7
Acacia erube scens Fabaceae Moloto 45.9 24.62.5 1.5 5.6 1.7 8.9
Albizia anthelm intica Fabaceae Monoga 37.5 13.82.5 1.2 3.1 2.0 6.3
Gymlensis C M
Comum C M
C Eue Mo
Combre nseF Coae M
ata 1
B Ce M
Combretucense Co Mone
Grewia bicolor Tiliaceae Mogwana 0.2 0.8 0.0 0.0 0.2 0.0 0.2
100 100 100
Acacia eriolobaF Fabaceae Mogotho37.0 27.04.6 1.4 6.5 3.5 1.4
nosporia seneg aelastraceaeothono 36.3 20.80.3 1.2 4.8 0.2 6.3
Terminalia pr uni oi d e s ombretaceaeotsiara 35.9 21.42.3 1.2 4.7 1.8 7.7
Gardenia volkensii Rubiaceae Morala 26.1 6.1 0.6 0.9 1.4 0.4 2.7
Mimusops zeyheri Sapotaceae Mmupudu 23.9 0.2 0.8 2.7 0.1 3.6
bretum albo p unctatombretaceaeotsoketsane20.4 22.81.8 0.7 4.9 1.2 6.8
Ximenia amer icana Olacaceae Moretologa 13.0 8.5 0.0 0.5 2.2 0.0 2.7
roton megalobotrysFphorbiaceatsebe 11.9 2.2 0.5 0.4 0.5 0.3 1.2
Dichrostac hys ciner ea Fabaceae Moselesele10.5 5.20.1 0.4 3.5 0.1 4.0
Grewia flava Tiliaceae Moretlwa 7.6 16.80.0 0.3 3.7 0.0 3.9
tum hereroembretaceokabi 6.9 2.2 0.4 0.2 0.5 0.2 0.9
Grewia retinervis Tiliaceae Mokgomph5.5 3.00.0 0.2 2.9 0.0 3.1
Acacia galpinii Fabaceae Mokala 2.6 0.7 0.2 0.1 0.2 0.1 0.4
oscia albitruncaapparaceaotopi 1.8 5.9 2.8 0.1 1.4 2.2 3.7
phus mucron ataFRhamnaceae Mokgalo1.4 2.3 0.0 0.0 0.5 0.0 0.6
Acacia nilotica Fabaceae Motlhabakgo1.2 0.8 0.0 0.1 0.2 0.0 0.3
Acacia fleckiiF Fabaceae Mohahu 0.6 0.8 0.5 0.0 0.2 0.4 0.6
m mossambimbretaceaetsweketsa0.6 0.8 0.0 0.0 0.2 0.0 0.3
Philenoptera v iolacea Fabaceae Mopororo 0.4 1.6 0.4 0.0 0.3 0.3 0.7
Unidentified species - - 0.4 0.8 0.5 0.0 0.2 0.4 0.6
*The “0” values indicate several decimal places, i.e. close to zero; F = species most preferred for fencing (Chimbari et al., unpublished).
imilarities in Composition of Woody Species
oth sites
Density, Frequency and Dominance
cies were 2745.7 ±
± 36 (SD) (range
Of the 46 woody species, 22 were recorded at b
hile 5 and 19 woody species were recorded only from Xobe
and Shorobe sites, respectively (Tables 1 and 2). The similari-
ties of woody species in terms of richness of species, genera
and families at the two sites were about 50%, 54% and 56%, re-
The total mean densities of woody spe
1.35 (SD) (range = 2222 - 6545) and 4269.7
55 - 3133) individuals ha1 at Xobe and Shorobe, respec-
tively, and ranged from 0.2 (G. discolor) - 1194.3 (A. mellifera)
at Xobe and 0.2 (E. divinorum) - 1675.4 (C. mopane) (Tables 1
and 2). Despite differences in absolute numbers, the total mean
Table 2. 12 1
List of woody species recorded from Shorobe with their densities (individuals ha), frequencies (%), dominance (m·ha ), relative values (%) of
densities, frequencies and dominance as well as Important Value Index (MDE = mean density, MF = mean frequency, MDO = mean dominance,
RMDE = relative mean density, RMF = relative mean frequency, RMDO = relative mean dominance and IVI = important value index).
Species Family Local names MDE MF MDO*RMDE RMF RMDO
Colopho opaneF spermum mFabaceae Mophane 1675.439.987.6 25.7 6.2 26.5 58.5
Acacia tortilisF Fabaceae Mosu 509.8 71.434.9 14.7 10.3 16.6 41.6
Acacia eriolobaF Fabaceae M
Co F C
Gs Ma
Gyms C
Combse C
Rhm Bi
M e
Te F C M
ogotho468.6 81.642.5 10.7 12.0 20.6 43.3
ilenoptera violaceFabaceae Mopororo 258.3 48.920.4 7.7 7.0 9.9 24.6
Dichrostac hys ciner ea Fabaceae Moselesele 218.4 59.34.0 6.8 8.6 2.2 17.6
Hyphaene p etersiana F Arecaceae Mokolwane 175.7 41.80.0 5.1 5.9 0.0 11.0
Grewia bicolor Tiliaceae Mogwana 175.1 29.52.1 7.1 4.5 0.9 12.5
mbretum imberbeombretaceaeMotswere 174.7 40.222.8 6.5 5.7 10.3 22.5
Croton me ga lobotry sF Euphorbiaceae Motsebi 133.5 21.815.9 3.5 3.3 6.9 13.7
Grewia flava Tiliaceae Moretlwa 88.1 33.60.6 2.0 5.2 0.2 7.4
rewia retinerviTiliaceae okgomphatl71.0 38.80.6 2.2 5.6 0.3 8.2
Acacia melliferaF Fabaceae Mongana 69.4 24.60.5 1.9 3.3 0.2 5.4
nosporia seneg ale nsielastraceaeMothono 39.9 11.40.6 1.0 1.5 0.4 3.0
Ziziphus mucronataF Rhamnaceae Mokgalo 36.0 25.92.0 1.1 3.5 1.1 5.7
ombretum hereroenseFCombretaceae Mokabi 33.1 18.91.3 1.0 2.7 0.6 4.3
Rhus tenuinervis Anacardiaceae orupaphir24.2 18.90.2 0.7 2.8 0.1 3.6
Acacia nilotica Fabaceae otlhabakgosi 12.5 7.0 0.5 0.3 0.9 0.3 1.5
retum mossambicenombretaceaeMotsweketsane 12.2 5.3 0.4 0.3 0.8 0.2 1.2
Boscia albitrunca Capparaceae Motlopi 8.8 13.71.2 0.2 2.0 0.4 2.5
lbizia anthelmintica Fabaceae Monoga 8.5 2.6 0.5 0.2 0.4 0.4 1.0
Diospyros lycioides Ebenaceae Letlhajwa 6.4 6.8 0.0 0.1 0.9 0.0 1.1
Berchemi a discolour Rhamnaceae Motsentsela 4.8 1.0 0.6 0.2 0.2 0.3 0.6
Acacia heb eclada Fabaceae Setshi 4.7 0.9 0.2 0.1 0.1 0.1 0.3
igozum brevispinosugnoniaceae Lebuta 4.5 0.9 0.0 0.1 0.1 0.0 0.2
ommiphora mossabicensis Burseraceae Moroka 4.3 9.4 0.1 0.1 1.5 0.0 1.6
Terminalia pr uni oi d e s Combretaceae Motsiara 4.2 3.7 0.6 0.1 0.5 0.3 1.0
Grewia flavescens Tiliaceae otsotsojan3.2 6.0 0.0 0.1 0.9 0.0 1.0
Ximenia amer icana Olacaceae Moretologa 3.1 5.3 0.0 0.1 0.8 0.0 0.9
Acacia sieberianaF Fabaceae Moremostlha 2.4 2.6 0.1 0.1 0.3 0.1 0.5
Albizia harveyi Fabaceae Molalakgaka 2.3 2.0 2.2 0.1 0.3 0.9 1.3
imusops zeyheri Sapotaceae Mmupudu 2.1 0.9 0.0 0.0 0.1 0.0 0.2
nidentified species - otorokofina1.9 0.9 0.0 0.0 0.1 0.0 0.2
Acacia nigresc ensF aceMokoba 1.7 2.6 0.0 0.0 0.3 0.0 0.4
Philenoptera ne lsii Fabaceae Mohatha 1.7 1.7 0.0 0.0 0.3 0.0 0.3
Capparis tomentosa apparaceae Motawana 1.5 1.0 0.2 0.1 0.2 0.1 0.3
Combretum collinum Combretaceae Modubana 1.3 0.9 0.8 0.0 0.1 0.2 0.4
Acacia fleckiiF Fabaceae Mohahu 0.4 0.9 0.0 0.0 0.1 0.0 0.1
rminalia serice aombretaceaeogonono0.4 1.7 0.0 0.0 0.2 0.0 0.3
Garcinia livingstoneiF Clusiaceae Motsaudi 0.3 1.0 0.0 0.0 0.2 0.0 0.2
Acacia erube scensF Fabaceae Moloto 0.2 0.9 0.0 0.0 0.1 0.0 0.1
Euclea divinorum Ebenaceae Motlhakola0.2 0.9 0.0 0.0 0.1 0.0 0.1
269.7 100 100 100
*The “0” values inveral decimal places, i.e. cloo; F = species st preferred ng (Cbari et unpubli
dicate sese to zermofor fencihimal.,shed).
Copyright © 2013 SciRes. 143
ensities of woody species at both sites did not exhibit logical importance. Nine and 16 species had IVI d
significant differences (Students T-Test, P = 0.35).
The top 10 densest woody species at Xobe were (in de-
eckii, A. galpinii, A.
at Xobe were (in
Important Value Index
Value Index, Acacia mellifera, A.
values of less
lation S tr uct ur e and Regeneration Status
cies re-
to five
meter class and
rn as the first group except that
coppice recruitment and missing of individuals
lasses. To this group
irst diameter class or juveniles. This group
Forest and woodland tswana are important in
providing socio-economl services, e. g. timber,
ending order of density) Acacia mellifera, A. tortilis, Philen-
optera nelsii, Acacia luederitzii, A. erioloba, A. erubescens,
Terminalia prunioides, Combretum albopunctatum, Albizia an-
thelmintica and Gymnosporia senegalensis (Table 1). The least
five densest woody species at Xobe were (in descending order
of density) Acacia fleckii, Combretum mossambicense, Philen-
optera violacea, Unidentified sp. and Grewia bicolor. The 10
densest woody species at Shorobe were (in descending order of
density) Colophospermum mopane, Acacia tortilis, A. erioloba,
Philenoptera violacea, Dichrostachys cinerea, Hyphaene pe-
tersiana, Grewia bicolor, Combretum imberbe, Croton mega-
lobotrys and Grewia retinervis (Table 2). The least five densest
woody species at Shorobe were (in descending order of density)
Acacia fleckii, Terminalia sericea, Garcinia livingstonei, Aca-
cia erubescens and Euclea divi norum.
Acacia erioloba, A. erubescens, A. fl
ederitzii, A. mellifera, A. nilotica, A. tortilis, Albizia anthel-
mintica and Boscia albitrunca were the ten most frequent
woody species at Xobe (in descending order of frequency)
(Table 1). The five least frequent woody species were Philen-
optera violacea, Terminalia prunioides, Unidentified species,
Ximenia americana and Ziziphus mucronata. Acacia erioloba,
Acacia tortilis, Dicrostachys cinerea, Philenoptera violacea,
Hypaene petersiana, Combretum imberbe, Colophospermum
mopane, Grewia retinervis, G. flava and G. bicolor were the
top 10 most frequent species in Shorobe (in descending order of
frequency) (Table 2). The five least frequent woody species
were Combretum collinum, Acac i a fl eckii, Garcinia livingstonei,
Acacia erubescens and Euclea divinorum.
The top 10 most dominant woody species
scending order of dominance) Acacia tortilis, A. mellifera,
Philenoptera nelsii, Acacia luederitzii, A. erioloba, Boscia albi-
trunca, Acacia erubescens, Albizia anthelmintica, Terminalia
prunioides and Combretum albopunctatum (Table 1). Seven
woody species (22% the total number of species recorded at the
site) had very insignificant dominance values, i.e. close to zero.
These are Ximenia americana, Grewia flava, Ziziphus mucro-
nata, Acacia nilotica, Combretum mossambicense, Grewia
bicolor and the unidentified species. The top 10 most dominant
woody species at Shorobe were (in descending order of domi-
nance) Colophospermum mopane, Acacia erioloba, Acacia tor-
tilis, Combretum imberbe, Philenoptera violacea, Croton me-
galobotrys, Dichrostachys cinerea, Grewia bicolor, Ziziphus
mucronata and Albizia harveyi (Table 2). Sixteen of the woody
species (about 39% of the total number of species recorded at
the site) had very insignificant dominance values, i.e. close to
Based on their Importance
rtilis, Philenoptera nelsii, Acacia luederitzii, A. erioloba, A.
erubescens, Terminalia prunioides, Combretum albopunctatum,
Albizia anthelmintica and Gymnosporia senegalensis in Xobe
(Table 1) and Colophospermum mopane, Acacia erioloba, Aca-
cia tortilis, Philenoptera violacea, Combretum imberbe, Di-
chrostachys cinerea, Croton megalobotrys, Grewia bicolor,
Hyphaene petersiana and Grewia retinervis in Shorobe (Table
2) were the top ten species in their descending order of eco-
than one in Xobe and Shorobe, respectively, indicating that
they are the least ecologically important species (Tables 1 and
Based on their population structures, the woody spe
corded at Xobe and Shorobe could be categorized in
ameter class distribution patterns (Figure 5).
The first group was composed of species that exhibited
higher number of individuals at the lowest dia
ogressively declining numbers with increasing diameter
classes. To this group belonged Acacia erioloba, A. tortilis, A.
mellifera, Colophospermum mopane, Combretum imberbe, Di-
chrostachys cinerea, Grewia retinervis and Gymnosporia sene-
galensis at Shorobeand Combretum albopunctatum, Dichro-
stachys cinerea, Gymnosporia senegalensis and Ximenia ame-
ricana at Xobe (Figure 5(a)).
The second group was composed of species with similar di-
ameter class distribution patte
dividuals are missing at the higher diameter classes. To this
group Commiphora mossabicensis, Diospyros lycioides, Gre-
wia flavescens and Rhus tenunervis at Shorobe and Acacia
luederitzii, A. tortilis, Albizia anthelmintica, Terminalia pruni-
oides and Ziziphus mucronata at Xobe (Figure 5(b)) have been
The third group consisted of species that showed both ham-
pered seedling/
the higher diameter classes. To this group belonged Acacia
hebeclada, A. nilotica, A. sieberiana, Albizia anthelmintica,
Combretum hereroense, C. mossambicense, Croton megalo-
botrys, Grewia bicolor, Mimusops zeyheri and Ziziphus mu-
cronata at Shorobe and Acacia erubescens, A. galpinii, A. mel-
lifera, Combretum hereroense, C. mossambicense, Croton me-
galobotrys, Gardenia volkensii, Mimusops zeyheri and Philen-
optera violacea at Xobe (Figure 5(c)).
The fourth group was composed of species with missing in-
dividuals in one or more of the diameter c
lbizia harveyi, Berchemia discolor, Boscia albitrunca, Cap-
paris tomentosa, Combretum collinum, Grewia flava, Philen-
optera violacea and Terminalia prunioides at Shorobe and Aca-
cia erioloba, A. fleckii, A. nilotica, Boscia albitrunca, Philen-
optera nelsii and the unidentified species at Xobe (Figure 5(d))
were categorized.
The fifth group consisted of species with individuals repre-
sented only in the f
as composed of Acacia erubescens, A. fleckii, A. nigrescens,
Euclea divinorium, Garcinia livingstonei, Hyphaene petersiana,
Philenoptera nelsii, Rhigozum brevispinosum, “Motorokofina”
(unidentified sp.), Terminalia sericea and Ximenia Americana
at Shorobe and Grewia bicolor, G. flava and G. retinervis at
Xobe (Figure 5(e)).
resources in Bo
ic and ecologica
od, fuelwood, traditional medicine, fodder, other non-timber
forest products, source of grazing areas, wildlife habitats, tour-
ism, watershed regulation, soil protection, carbon sequestration
and storage, etc., that sustain livelihoods of communities and
Copyright © 2013 SciRes.
(a) (b)
(c) (d) (e)
Figure 5. structure of woody species recorded at Shorobe ((a) and (e)) and Xobe ((b), (c) and (d)) [diameter class (DBH): 1 = <2 cm; 2 = 2 - 5 cm;
e national economy. Therefore, their sustainable management,
central role in ecology
highest species
(Luoga et al., 2000; Banda et al., 2008) and Uganda (Nangendo
be a
ra and families of woody species
3 = 5 - 10 cm; 4 = 10 - 15 cm; 5 = 15 - 20 cm; 6 = 20 - 25 cm; 7 = 25 - 30 cm; 8 = 30 - 35; 9 = 35 - 40; 10 = >40 cm.
utilization and conservation are crucial.
Measures of species diversity play a
d conservation biology (Magurran, 2004) since species di-
versity is an important parameter of a plant community, one of
the major criteria for nature conservation and connected to
ecosystem dynamics and environmental quality (Kalema, 2010).
A change in species diversity is often used as an indicator of
anthropogenic or natural disturbances in an ecosystem (Liu &
Brakenhielm, 1996; Kalema, 2010). Therefore, characterization
of biodiversity through inventories can be useful in the plan-
ning of operations that aim to conserve biodiversity (Belbin,
1995; Faith & Walker, 1996; Kelema, 2010).
Of the two study sites, Shorobe exhibited the
chness with 18 of the woody species not recorded from Xobe.
Only five of the species recorded at Xobe were not encountered
in the studied quadrats at Shorobe. Interestingly, even the
densest and most dominant tree species in northern Botswana,
namely C. mopane, and the common and conspicuous species,
such as H. petersiana and Combretum imberbe at Shorobe were
not recorded from the quadrats examined in Xobe, indicating
their scarcity at this study site. Conversely, one of the most
common species recorded in Xobe, namely A. leuderitzii, was
not encountered in the quadrats sampled from Shorobe. In addi-
tion, the numbers of genera and families were higher in
Shorobe than Xobe. With the exception of A. tortilis and A.
erioloba, the highest densities, frequencies, dominances and,
hence, IVI values were exhibited by different species in the two
sites. In terms of species richness and overall diversity, Shorobe
and Xobe had much lower number of woody species compared
with reports from studies in the Sudanian savanna in Burkina
Faso (Savadogo et al., 2007), dryland forests and woodlands in
Ethiopia (Woldemariam et al., 2000; Senbeta & Teketay, 2003;
Zegeye et al., 2006, 2011; Worku et al., 2012) as well as wood-
lands and forests in South Africa (Dovie et al., 2008), Tanzania
et al., 2006; Kalema, 2010). However, the evenness values of
woody species in Shorobe and Xobe were comparable with
those reported for other dry land forests (Senbeta & Teketay,
2003; Alelign et al., 2007; Zegeye et al., 2006, 2011).
The overall diversity of woody plants was much higher in
Shorobe (H’ = 2.18) than Xobe (H’ = 1.5), which may
nsequence of the high species richness in Shorobe. It has
been noted that the value of H’ obtained from empirical data
usually falls between 1.5 and 3.5, and rarely surpasses 4 (Mar-
galef, 1972; Magurran, 2004). This implies that the diversity of
woody species at Xobe falls at the lowest value of the diversity
range. Although we have not investigated the causes, the dif-
ference in the edaphic factors, especially the big difference in
the soil types and moisture availability (Chimbari et al., 2009),
may be responsible for the considerable floristic variations
(richness of species, genera and families as well as overall di-
versity) between the two sites. The diversity values of woody
species obtained at Shorobe and Xobe are lower than those
reported from Miombo Woodlands in Tanzania (Nduwamungu,
1997; Zahabu, 2001) and savanna woodlands in South Africa
(Dovie et al., 2008). However, evenness values of the woody
species at Shorobe (E = 0.6) and Xobe (E = 0.5) were more or
less similar, also with those from other studies (Zegeye et al.,
2006, 2011; Worku et al., 2012), suggesting that individuals of
the different species recorded exhibited moderately similar
abundance at the two sites.
The Jaccard’s Similarity Coefficients of about 50% - 56% for
the richness of species, gene
corded from the two sites indicate that about half of the total
species, genera and families encountered were specific to one
or the other site. This reality has to be taken into consideration
in any plan aimed at the sustainable management and conserva-
tion of these resources.
Shorobe exhibited much higher density of woody species
Copyright © 2013 SciRes. 145
compared with that of Xobe, which could be associated with
th more than 82% of the total density recorded
rded at Xobe may be attributed to seed
than Xobe while P. nelsii exhibited higher
ther dry Afromontane
cance of species in a given ecosys-
of the woody species recorded
e higher number of woody species encountered at Shorobe
than Xobe. With the exception of A. tortilis and A. erioloba, the
two study sites differed in their densest woody species. Sur-
prisingly, as stated above, the densest woody species in
Shorobe, C. mopane, was not recorded from any of the quadrats
assessed in Xobe, which may be attributed to its requirement of
habitats with heavy textured and poorly drained soils (Ellery &
Ellery, 1997).
A. mellifera and A. tortilis had much higher densities at Xobe
than Shorobe wi
Xobe. In fact, more than 87% of the total density in Xobe
was represented by the six Acacia species, five of which are
also among the most dominant and frequently found species
with the highest IVI values. This might suggest signs of bush
encroachment due to overgrazing and over-exploitation of re-
sources at Xobe (DEA, 2008). Acacia mellifera forms impene-
trable patches of thickets at Xobe and is known to encroach
eroded sites (Ellery & Ellery, 1997) and heavily grazed areas
(El-Sheikh, 2013). Acacia tortilis is also common and wide-
spread species in Botswana, which occurs on clay or loam soils
in a variety of woodlands, generally near floodplains and pans.
It tends to encroach heavily grazed sites (Ellery & Ellery, 1997).
The domination of Acacia species, which are indicative of
heavy grazing and encroachment, at Xobe is consistent with the
fact that Xobe is used as a cattle post by people living in the
nearby Maun Town.
In addition, the relatively high number of species and density
of Acacia species reco
spersal, which is known to be facilitated by ruminants, and
the subsequent favourable initial habitat for the developing
seedlings within the accompanying droppings of the animals
(Schultka & Cornelius, 1997; Teketay, 1996b, 1997b, 2005a;
Kalema, 2010). Many Acacia species also use the soil seed
bank as one route of regeneration after disturbance, especially
following fire incidences (Sabiiti & Wein, 1987; Teketay &
Granström, 1995, 1997; Teketay, 1998; Witkowski & Garner,
2000; Eriksson et al., 2003; Teketay, 2005a). It has been re-
ported that grazing is a predictable selective form of distur-
bance with animal behaviour through browse choice playing a
significant role in determining which species are impacted
(Whelan, 2001; Kalema, 2010). Grazing pressure may also play
a significant role in determining plant community structure and
composition by facilitating bush encroachment in frequently
grazed areas (Witkowski & O’Connor, 1996; Kalema, 2010).
Grazing, fire and selective tree harvesting, which are very
common in the study sites, are considered major disturbances
shaping species diversity and productivity (Savadogo, 2007;
Kalema, 2010).
It is interesting to note that P. violacea had much higher den-
sities at Shorobe
nsity in Xobe than Shorobe. On the one hand, P. violacea
grows in open woodlands on edges of islands in seasonal
swamps, and occasionally on interior regions of islands in per-
manent swamps (Ellery & Ellery, 1997), habitats common in
the surroundings of Shorobe. On the other, P. nelsii occurs in
deep sand as part of short woodlands (Ellery & Ellery, 1997),
which characterize the habitat at Xobe.
The overall density of woody species recorded at Shorobe
was higher than those reported from o
rests (Alelign et al., 2007; Zegeye et al., 2006, 2011) and
woodlands (Worku et al., 2012). The overall density of woody
species recorded at Xobe was higher than other dry woodlands
(Worku et al., 2012), similar to those reported from different
forests (Woldemariam et al., 2000; Zegeye et al., 2006, 2011)
and lower than other dry Afromontane forests (Alelign et al.,
2007; Zegeye et al., 2011). The overall horizontal distribution
of the woody species, represented by the frequency of occur-
rence of the species in the studied quadrats, was relatively low
with only 10 (out of 41) and three (out of 27) species having
more than 30% frequency values at Shorobe and Xobe, respec-
tively. This implies that the other species have scarce horizontal
distribution at both study sites, which requires further investi-
gations that can assist in the future design of appropriate man-
agement interventions.
Importance Value Index is an important parameter that re-
veals the ecological signifi
m (Lamprecht, 1989; Zegeye et al., 2006; Senbeta & Teketay,
2003; Worku et al., 2012). Acacia mellifera, A. tortilis and
Philenoptera nelsii at Xobe and Colophospermum mopane,
Acacia erioloba, Acacia tortilis and Philenoptera violacea at
Shorobe can be considered the most ecologically important
woody species with IVI values of more than 20 contributed by
their high values of density, frequency and dominance. It is
interesting to note that A. tortilis is recorded among the most
ecologically important woody species at both study sites.
In the absence of long-term demographic data on population
trends, the use of diameter class distributions of woody sp
om a single survey has been shown to be a potential and reli-
able tool to reveal status of population structures and regenera-
tion of woody species as well as predict responses of the spe-
cies to disturbance and resultant changes in population structure
(Condit et al., 1998; Lykke, 1998; Obiri et al., 2002; Sokpon &
Biaou, 2002; Teketay, 2005a, 2005b; Feeley et al., 2007; Tabuti,
2007; Mwavu & Witkowski, 2009a; Tesfaye et al., 2010;
Venter & Witkowski, 2010; Sop et al., 2011; Helm & Wit-
kowski, 2012; El-Sheikh, 2013). A population size structure is
simultaneously the outcome of past demographic events and an
indicator of its demographic future (Wilson & Witkowski, 2003;
Kalema, 2010).
Based on the assessment of diameter class distributions, the
population structure patterns
om Shorobe and Xobe were categorized into five groups. The
species in the first group exhibited reverse J-shaped distribution,
which is widely acknowledged to indicate stable population
structure, naturally replacing senesced individuals with seed-
lings and saplings (Condit et al., 1998; Lykke, 1998; Obiri et al.,
2002; Teketay, 1997a; 2005a, 2005b; Tabuti, 2007; Mwavu &
Witkowski, 2009a; Tesafye et al., 2010; Sop et al., 2011; Helm
& Witkowski, 2012; El-Sheikh, 2013). This appeared to be the
case for about 20 and 15% of the woody species recorded at
Shorobe and Xobe, respectively. Typical examples are A. erio-
loba, A. tortilis and C. mopane at Shorobe and C. albopunc-
tatum and G. senegalensis at Xobe. The species in the second
group exhibited relatively good recruitment (of seedlings/cop-
pices) but the regeneration is negatively affected as evidenced
from the absence of individuals in progressively higher classes.
This may be attributed to either natural- or human-induced
hampered regeneration. Pole-sized and mature individuals may
have been cut by the local people for various purposes. This
group was comprised of about 10 and 19% of the woody spe-
cies recorded at Shorobe and Xobe, respectively. The species in
the other groups exhibited both naturally- and human-induced
disturbances leading to their hampered regeneration. This ap-
Copyright © 2013 SciRes.
peared to be the case for about 70% and 66% of the woody
species recorded at Shorobe and Xobe, respectively. In parti-
cular, the species in the fifth group, represented by about 27%
and 11% of the woody species recorded at Shorobe and Xobe,
respectively, exhibited a very serious problem of regeneration
with individuals only in the first diameter class.
Some of the causes for the hampered regeneration of the
woody species include clearing of the woody vegetation for
es and cutting of trees of woody spe-
species (Tables 1 and 2) are most
The results revealed Xobe together house
46 different woody specde the local communi-
that indi-
e. Also, relatively low evenness indices, which were
e problems described above.
ing the
regulate or promote the type, diameter and height
ltivating crops both by molapo (Figure 2(A)) and dry land
(Figure 3(B)) farmers, heavy grazing pressure, cutting of stems
and lopping of branches of woody species for fencing of farms
(Figures 2(A) and (B), 3(B)), kraals (Figure 3(A)) and house
compounds and fuel wood. A land use assessment carried out
by the University of Botswana on the basis of satellite images
found that of the 48,900 ha cleared for cultivation in Ngamiland,
75% consist of dryland fields and 25% of fields in temporarily
inundated floodplains (VanderPost, 2009). VanderPost (2009)
also indicated that molapo farming takes place on small fields
separated by strips of “natural” floodplain, and wholesale land-
clearing does not usually occur, although removal of some
vegetation takes place.
The major impact of the molapo farming results from the
heavy lopping of branch
es used for fencing the farms. The heavy lopping of branches
of woody species will negatively affect the production of
fruits/seeds in enough qunatities required for the stable recruit-
ment and regeneration of the species. However, the major im-
pact was observed from the clearing and grazing (Figure 3(B))
of considerable areas of woody vegetation for the purpose of
establishing and fencing rain-fed dry land farming (Figure
3(B)). In addition, the free grazing system in the study sites in
particular and Botswana in general leads to the browsing and
trampling of seedlings of woody species. At Shorobe, H. peter-
siana was categorized in the fifth group based on its population
structure. The trees of this species are cut down at about 30 cm
above the ground for tapping the stem sap, which is, then, proc-
essed by the local people to produce palm wine (Babitseng &
Teketay, 2012). This traditional wine tapping method, which
leads to the destruction of the stems of trees, is responsible for
the obvious population structure (Figure 5(e)) and, hence,
hampered regeneration.
The socio-economic survey carried out at the two study sites
revealed that 15 woody
eferred for fencing, especially molapo farms (Chimbari et al.,
unpublished). Of these, 10 and five species recorded at Shorobe
and Xobe, respectively, belong to the last three groups of
population structure patterns. Six of the species recorded at
Shorobe belong to the fifth group of the population structure
pattern. This suggests that cutting of woody species for fenicng
is contributing to the observed hampered regeneration of the
species. If it is not properly managed, clearing of woody vege-
tation, cutting and lopping trees excessively, coupled with an-
nual recurrent fires common in the study sites and elsewhere in
Botswana, will affect the population structure of woody species
negatively and, hence, reduce or prevent their potential of re-
generation and, therefore, perpetuation. This will, in turn, result
in the decline or loss of biodiversity ultimately. Whelan (1995)
argues that frequent fire outbreak can affect population struc-
ture through elimination of certain classes or a delay in the
whole recruitment process. Though information on fire toler-
ances for woody species is not available, fire might have caused
the poor representation of individuals of some of the woody
species since farmers use fire to clear woody vegetation for
grazing and for farming.
that Shorobe and
ies, which provi
s with various goods and services. Despite the apparent im-
pacts from humans, domestic animals and recurrent annual fires,
some of the woody species exhibited desirable values of density,
frequency, dominance, IVI, population structures and regenera-
tion status. Shorobe Village exhibited higher values of species,
genus and family richness as well as relatively high diversity
and overall density of woody species than Xobe Village. This
may be attributed to the difference in the edaphic factors, espe-
cially the big difference in the soil types and moisture availabil-
ity, as well as the relatively higher human- and domestic ani-
mal-induced disturbances at Xobe than Shorobe. The similari-
ties of woody species in terms of richness of species, genera
and families were medium suggesting that each site has its own
characteristic species, genera and families. This is particularly
important to consider when planning activities aimed at the
responsible management, sustainable utilization and conserva-
tion of the woody vegetation at the study sites.
At both sites, the frequency of woody species was relatively
low with the exception of a few species, suggesting
duals of the species are thinnly or very thinnly spread hori-
zontally. This is also evident from the medium evennes values
recorded from the two study sites. Some of the woody species,
especially those categorized in population structure Groups 3-5,
exhibited negatively affected popultion structures and, as a
result, hampered regeneration, which requires special attention
and appropriate management intervention by the concerned
The results revealed relatively low diversity and overall den-
sity at Xob
used by the sparse to very sparse horizontal distribution of
individuals, were recorded at both sites. Many of the woody
species exhibited low values of densities, basal areas and IVI
values, unstable population structure and hampered regenera-
tion at both study sites. These results indicate the need for at-
tention and appropriate management interventions by the rele-
vant national authorities at various levels, including the Kgosi
(Chiefs), Village Development Committees and local commu-
nities of the study sites.
The following are a few examples of feasible management
interventions to address th
1) Reduction of the pressure on regeneration of the woody
species from the uncontrolled grazing through match
rrying capacity of the study sites with appropriate numbers of
2) Introduction of management plans and appropriate tech-
nologies that
asses, and number of individuals of the available woody spe-
cies to be harvested for the various needs of the communities.
To this effect, we are also undertaking an experiment focusing
on the effect of cutting diameter and height on the re-sprout-
ing/coppicing ability of selected woody species at the study
sites (Neelo et al., unpublished) with the aim of determining the
optimal cutting diameter size(s) and height(s) for maximum
re-sprouting ability of the species. Once promising results are
achieved, it is hoped that the optimal cutting diameter(s) and
Copyright © 2013 SciRes. 147
height(s) will be demonstrated and disseminated to the local
communities to promote desirable regeneration of the woody
species with appropriate and sustainable utilization.
3) Establishment of rotational exclosures (Mengistu et al.,
2005; Birhane et al., 2006; Aerts et al. 2009) of the areas cov-
h hampered re-
ructures, regeneration and perpetuation of
Authors are graDevelopment Re-
search Centre (IDl support for this
Aarrestad, P. A., Masu, Pitlagano, M. L.,
Marokane, W., & Ska of soil, tree cover and
ed with woody species at both sites, from both human and
animal disturbances, so that the species will get enough time
and appropriate environmental conditions to recover from the
heavy grazing that affected their regeneration.
4) Research on the life-cycle and propagation (both sexual
and asexual) methods of the woody species wit
neration to promote their assisted regeneration, e.g. through
enrichment planting.
5) Creation of awareness of the local communities on the
status of population st
e woody species in their localities so that they can promote
responsible management and utilization as well as conservation
of the species.
teful to the International
RC) for providing financia
udy through the Botswana Ecohealth Project. We are thankful
to Kgosi (Chiefs), Village Development Committees and local
communities of the study sites, field technicians and Transport
Section of the Okavango Research Institute (ORI), University
of Botswana, community research assistants and Peter Smith
University of Botswana Herbarium (PSUB). We are grateful to
Chenamani Ntogwa for allowing us to use his compass and
caliper and Amanda Tas for her voluntary help to collect, or-
ganise and analyse our data. We would also like to thank ORI
and its management for its logistical support.
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