Journal of the
Drylands
ISSN 1817 - 3322
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JOURNAL OF THE DRYLANDS 3(1): 165-180, 2010
Floristic Diversity and Structure of Nechisar National Park, Ethiopia.
Samson Shimelse1*, Tamrat Bekele2 and Alemayehu Mengistu3
Samson Shimelse, Tamrat Bekele and Alemayehu Mengistu. 2010. Floristic Diversity and Structure of Nechisar
National Park, Ethiopia. Journal of the Drylands 3(1): 165-180
A study was conducted in Nechisar National Park, Ethiopia with the objectives of investigating the floristic
composition and structure of the Park. Representative sites at an altitudinal range of 1150m – 1440m were selected
with stratified random sampling design and a total of 70 plots with the size of 20m x 20m at an interval of 150m to
200m were laid along the established transect lines. For the assessment of herbaceous biomass, five sub quadrants
each with the size of 1m x 1m were established at four corners and center of every quadrant. The cover abundance
values, density and diameter at breast height and list of species were recorded in each plot. Two hundred eight species
belonging to 56 families and 124 genera were identified and documented. Analysis of vegetation data reveled 5
homogeneous clusters. The density of trees is 887 individuals ha-1. The basal area is about 49.45m2 ha-1. The
population structures of tree species were assessed and these had clearly signaled the occurrence of cutting of selected
diameter classes of ecologically, economically and medically important tree species for various purposes, particularly
for fuel wood and species like Sterculea setigera have poor reproductive capacities of its old individuals so the
regeneration ecology and reproductive biology of this and the other species should be investigated in studies.
Key words/phrases: Nechisar National Park, Floristic composition, Population structure and Vegetation.
1
Mekelle University, PO Box 231, Mekelle, Ethiopia.
Email. samshimelse@yahoo.com.
2
Department of Biology, Faculty of Science, Addis Ababa University, PO Box 3434, Addis Ababa,Ethiopia.
3
PO Box Urael Branch, 62291 Addis Ababa, Ethiopia. Email. alemayehumengistu@yahoo.com
Corresponding author’s address: Email: samshimelse@yahoo.com
Received October 20, 2009, Accepted May 15, 2010.
INTRODUCTION
Ethiopia is one of the countries in the world that
posses a unique characteristic fauna and flora
with a high level of endemism (Tewoldebirhan,
1989). The topographic features that range from
110 meters below sea level to 4620 meters above
sea level has created quiet diverse ecological
conditions in the country. This wide range of
ecological
variation
coupled
with
the
corresponding diverse socio-culture has made the
country to be one of the important diversity rich
areas in the world. Large species of trees, shrubs,
herbs, cultivated plants and their wild relatives are
found in the different agro-ecological zones of the
country (Tadesse, 2003; Alemayehu et al., 2005).
According to Hedberg (2009), there are about
6,000 species of higher plants included in the
Ethiopian flora. Of these, about 10% are endemic
species (Vivero et al., 2006). Due to this reason,
Ethiopia is the fifth major country in tropical
Africa in terms of the diversity of flora (Ensermu,
et al., 1992). In addition, it is known worldwide as
one of the global centers of biodiversity so that
much of this biodiversity is associated with forest
resources (Yonas, 2004). However, the wildlife
resources and their natural habitats in Ethiopia are
facing various problems due to population
pressure, poverty, inappropriate farming systems,
climatic changes and other related problems
(Shibru, 1995; Tesfaye, 1997).
Copyright © Journal of the Drylands 2010
ISSN 1817-3322
Nechisar NP was proposed in 1967 and the
boundaries were designated and the Park was
established in 1974 because the area has
considerable natural beauty and large number of
wild animals, all of which survive to present day
except for the African Buffalo. However, this Park
is not yet gazetted. The problems are more
intensified and the wildlife population has
gradually declined from time to time. Some of the
major problems that contribute to the destruction
of natural habitats, and hence wildlife in NNP
were overgrazing by livestock, deforestation for
agricultural expansion and harvesting fuel wood
(charcoal and firewood) (NNP annual report,
2010).
For effective management and conservation
of this unique ecosystem of the country, there is
an urgent need to develop a sound management
plan, and this, in turn, required detailed baseline
information on the ecology of the area. However,
the floristic composition, plant community and
structural analysis of the NNP have not previously
investigated in detail except limited study made
by Tamrat in (2001) that covers some parts of the
Park. Therefore, the present study was conducted
with the objective of determining the floristic
composition; identify plant communities and
carryout structural analysis of NNP. Which is the
main component and that should be studied for the
well being of the Park and healthiness of the
165
games that it supports and contribute a lot to the
effort being made in the development of a sound
management plan for effective conservation of the
park resources.
MATERIAL AND METHODS
The study area
The study was conducted in NNP (also spelled as
Nech Sar) is one of the National Parks of
Ethiopia. Located at about 510 km away from
Addis Ababa, in the Amaro Special Woreda and
Arbaminch Zuria Woreda of the Southern Nation
Nationalities and Peoples Regional State
(SNNPRS). It is situated to the east of Arbaminch.
Its 514 square kilometers of territory include the
"Bridge of God" (an isthmus between Lakes
Figure 1. Map showing the study area
The annual rainfall is bimodal with a long rainy
season during April to June and short rainy season
from September to November. The mean annual
rainfall is 919.08 mm. Annual maximum and
minimum temperature are 30.520C and 17.30C,
respectively (Fig. 2).
NNP lies within the Somalia - Massai
Regional Center of Endemism vegetation
description (White, 1983). Out of the 2,500 plant
species of this regional center of endemism,
around 800 -1000 species are estimated to be
found around the NNP (Evans et al., 1992). The
undulating hills between the lakes and the
highlands on the western and eastern escarpments
of the Rift Valley, which are within the premises
of the Park, are covered by diverse vegetation
types. The Park habitats can be grouped under
four major types of vegetation, the SomaliaMassai Acacia-Commiphora deciduous bush land
and Thicket, the Somalia-Massai edaphic
grassland, the Somalia-Massai riverine forest and
herbaceous freshwater swamp and aquatic
vegetation (Bolton, 1970; White, 1983; Kirubel,
1985; Duckworth, 1992; Evans et al., 1992;
Hillman, 1993). Among these, only the mix of two
Copyright © Journal of the Drylands 2010
ISSN 1817-3322
Abaya and Chamo), and the Nechisar (English:
white grass)
The Park is situated at 50 51`- 60 10` N and
0
37 32`-370 48` E (Fig. 1) with altitude ranges of
1108 masl at Lake Chamo and 1690 masl at the
peak of Geda hill. The Park covers an area of 514
km2 of which 436 km2 is covered by land. The
remaining area, 78 km2 is water. The Park is
located in the very scenic part of the Rift Valley
floor between the two lakes, Lakes Abaya and
Chamo (NNP Annual Report, 2010). The rugged
mountainous parts of the Park have a brown
calcareous loamy soil derived from volcanic
rocks. The plains of the NNP have black cotton
soil with high proportion of clay (Bolton, 1970;
Kirubel, 1985; Svitálek, 2007).
Figure 2. Climadiagram (after Walter, 1985)
showing rainfall distribution and
temperature variation from 1996 - 2009 at
Arbaminch meteorological station
Source: Raw data obtained from NMSA
(2010)
vegetation types, the Somalia-Massai edaphic
grassland (cover large proportion of the Nechisar
plains and highly dominated by common grass
species) and the dispersed Somalia-Massai
Acacia-Commiphora deciduous bushland and
thicket (cover small proportion of the Nechisar
plains, which is composed of thicket forming low
bushy trees and scattered shrubs set in and around
the plains) (Kirubel, 1985; Duckworth, 1992;
Evans et al., 1992; Yihsehak et al., 2007).
Dichrostachys cinerea and Acacia melifera
are the species responsible for the ongoing bush
encroachment seen in the Nechisar plains
(Svitálek, 2008). So clearly the encroachment
decreases the cover of the savanna grassland
reported by Bolton in 1970. The current status of
the Nechisar plains vegetation has not been well
studied quantitatively. It is believed that the
habitat has been degraded, especially in Dache
and there is ongoing bush encroachment on the
plain areas due to the impact of various activities
in connection to agriculture, cattle grazing and
unsustainable firewood collection by people living
in and around the Park (Yisehak, et al., 2007;
166
Svitálek, 2008). Details of the vegetation type
from this study in NNP are given in Table 1.
NNP harbors a variety of mammalian, avian,
amphibian, reptilian and fish fauna. There are 332
species of birds, belonging to 71 families of 22
orders reported from NNP areas. There are 84
species of mammals in NNP belonging to 27
families of 10 orders. Among the mammalian
fauna, four species are endemic to Ethiopia. One
of the endemic mammalian sub-species of the
Park is the Swayne's hartebeest (Alcelaphus
buselaphus swaynei). Out of the 84 species of
mammals in the Park, 10 species belong to the
Family Bovidae of the Order Artiodactyla
(Hillman, 1993).
Site selection and sampling design
A reconnaissance survey was carried out from 5 to
31 of August 2009, in order to have an impression
of the sampling sites and to determine the
sampling methods to be used for vegetation data
collection and physiognomy of the vegetation.
The field work was done with three subsequent
study trips, September 10 - October 25, 2009,
November 20 - December 10, 2009 and February
6 - 27, 2010. Since the area has different
formation types stratified random sampling
design, as described by Kent and Coker (1992)
was used to collect data on vegetation. Based on it
the following representative sites were selected: 1)
Scrubland, bush land and thicket, 2) Grassland, 3)
Shore (freshwater swamp and aquatic vegetation)
and 4) Riverine forest (woodland) were selected
by visual observation on the bases of homogeneity
in floristic composition. A total of 70 plots were
established in the different vegetation type. Each
vegetation stand was sampled using a systematic
sampling method. Quadrants of 20m x 20m
(400m2) were placed next to each other at the
interval of 150m to 200m. Altitude at each
quadrant was measured using Geographical
Positioning System (GPS) Garmin 72.
Vegetation data collection
A complete list of herbs (plants whose stem does
not produce woody, persistent tissue), shrubs
(woody plants having several stems at or near the
base of the plant and less than 3 m tall), climber
(woody plants which use trees and other means to
climb over the canopy) and trees (woody plants
having a dominant stem and more than 6 m tall)
were made in each plot. The percentage cover
abundance of all the vascular plants in each
quadrat were estimated and rated according to the
1-9 modified Braun- Blanquet scale (Van der
Maarel, 1979).
For all trees and shrubs, individuals taller
than 2 m and more than 2 cm in diameter were
measured for Height and Diameter at Breast
Height (DBH). In cases where a tree/ shrub bole
Copyright © Journal of the Drylands 2010
ISSN 1817-3322
branched at breast height or below, the diameter
was measured separately for the branches and
averaged as one DBH and in cases where
tree/shrub boles buttressed, DBH measurement
was undertaken from the point just above the
buttresses. In each sample plot, the total number
of individuals of woody species with diameter at
breast height (DBH) greater than 2 cm was
recorded. Within the main major plot of 400m2,
five sub- plots each 1m x 1m (1m2) were set up
one from the center and the rest from each corner
to be representative of the whole plot. These plots
were used to collect data on cover of herbaceous
species and the mean of the five sub-plots were
used in the analysis.
Plants in the vicinity but absent in the sample
plot were noted for floristic completion. Voucher
specimens of all plants in the study area were
collected, pressed, dried and identified at the
National herbarium of Ethiopia referring to the
published volumes of Flora of Ethiopia and
Eritrea. The nomenclature of plant names follows
the published volumes of flora of Ethiopia and
Eritrea (Hedberg and Edwards, 1989; Edwards et
al., 1995; Hedberg and Edwards, 1995; Edwards
et al., 1997; Edwards et al., 2000; Hedberg et al.,
2003; Hedberg et al., 2004; Hedberg et al., 2006),
and by comparing with authenticated specimens at
the National herbarium (ETH), Addis Ababa
University.
Data analysis
The Shannon diversity (H’) and evenness (E’)
indices were calculated as a measure to
incorporate both species richness and species
evenness. Both indices were calculated using the
software analysis package in PAST version 1.62
(Hammer et al., 2001). Vegetation data was
subjected to hierarchical cluster analysis
(classification) was made by using PC- ORD V
5.0 (McCune and Mefford, 1999) software. The
analysis was based on the abundance data of the
species. The Relative Euclidian Distance (RED)
measures using Ward’s method was used. The
Euclidian Distance was used because it eliminates
the difference in total abundance among sample
units; and the Ward’s method was used because it
minimizes the total within group mean of squares
or residual sum of squares (McCune and Grace,
2002). The identified groups were tested for the
hypothesis of no difference between the groups
using MRPP (Multi-Response Permutation
procedures) technique.
To analyze the population structure of the
vegetation, height and diameter frequency
distribution of all tree and shrub species was
employed using the measure of Height and DBH
for each species in all quadrats. Population
structure of tree stem diameter distribution has
been used to infer past disturbances, regeneration
167
patterns and successional trends in tree
populations (Tamrat, 1994; Demel et. al., 1997).
To determine the population structure, individuals
of each species encountered were grouped into ten
diameter class (2-10, 11-20, 21-30, 31-50, 51-70,
71- 90, 91- 110, 111-13, 131- 150 and > 150cm)
and height with a 3m after Tamrat, (1993) and
Haile et. al., (2008) and structure of the species
were depicted using frequency histogram of both
diameter and height class distributions following
Peters (1996). The resulted frequency histograms
of the study species, in particular were then
interpreted as an indication of regeneration status.
The following structural parameters were
calculated for some species following MuellerDombois and Ellenberg (1974) and Martin (1995).
% Frequency=
Number of plots a species occur
x 100
Total numbers of plots
Frequency of
Relative Frequency a spp. in the sample
=
x 100
(RF)
Total frequency of
all spp. in the sample
.
The No of individuals of that spp.
Density of a spp. =
Area sampled
No. of individuals of
a spp. in the sample
Relative Density =
x 100
Total No. of individuals of
all spp. in the sample
Basal area (m2) = (DBH/200)2 π
Where:
DBH = the diameter at breast height.
π = 3.14
Density of a species =
Total basal area
Area sampled
Dominance = Total basal area / area sampled
Area occupied by
a spp. in the sample (m2)
Relative
=
x 100
Total cover of
Dominance
all spp. in the sample (m2)
Relative
Importance Relative
Relative
=
+
+
Value Index Density Dominance Frequwncy
RESULTS AND DISSCUSSION
Floristic composition
A total of 208 vascular plant species belonged to
56 families and 124 genera were identified in this
study indicating that the area was more rich in its
plant diversity even from the afromontane forests
(Table 1) such as Jibat Forest (Tamrat, 1993)
Dakata Valley Forest (Demel, 1995a) Chilimo
Forest (Tadesse, 1998), Dodola Forest (Kitessa,
2003), Denkoro Forest (Abate, 2003), Mena
Angetu Forest (Ermias, 2005) and Yayu Forest
(Tadesse et al., 2008). The dominant families
occurring in the area were Fabaceae representing
26 (13 %) of species in 10 genera, and Poaceae by
Copyright © Journal of the Drylands 2010
ISSN 1817-3322
24 (12 %) in 18 genera (Table 1). Out of the total
plant species identified, about 91 species (44%)
were found to have ethnomedicinal use in
different study areas and their detailed
ethnomedicinal descriptions are already reported
(Ermias, 2005; Haile et al., 2007; 2008b; Tinsae,
2009).
Concerning the growth habits of the identified
species, 81 (39%) species were herbs, 78 (38%)
shrubs, 40 (19%) trees, 7 (3%) lianas and 2 (1%)
herbaceous climbers. Floristic composition of
given vegetation can be described in terms of its
richness in species, abundance, dominance, and
frequency (Lamprecht, 1989). Aloe otallensis was
found to be endemic to Ethiopia. The area also
contained major commercial indigenous tree
species indicated in EFAP, 1994. This tree species
include Celtis africana, Croton macrostachyus,
Prunus africana and Syzygium guineense.
Plant community types
Analysis of vegetation data using PC- ORD V-5
(McCune and Mefford, 1999) revealed five
clusters that could be recognized as plant
community types. Five plant community types
were also derived from the hierarchical cluster
analysis of SYN-TAX 2000 software. Community
groups in this dendrogram were determined at
70% dissimilarity level (Fig. 3). The data matrix
contained 70 plots and 118 woody species and the
analysis was done with PC- ORD V-5 software.
The decision on the number of groups was based
on the MRPP (Multi-Response Permutation
procedures) technique (no difference hypothesis)
and the ecological interpretation of the groups.
The test stastics T value for the groups were 38.095 (P < 0.001) and agreement statistics A was
0.0943. The test stastics T described the
separation between the groups. The more negative
T was, the stronger the separation. The agreement
statistics A describes within group homogeneity,
and falls between 0 and 1. When all items within
groups are identical, A=1 and 0 when the groups
are heterogeneous. In community ecology, values
of A (agreement) are commonly below
0.1(McCune and Mefford, 1999). In the result, a
species with a significant indicator value at P <
0.05 was considered as an indicator species of the
group (Table 2).
Community names employed below were
derived from species that had indicator values of
highest value, and which distinguished the
community by their high relative abundance and
relative frequency (Table 2). The description and
altitudinal distribution of this plant community
types is given below. Unfortunately this study did
not address analyses of a range of possible
environmental variables except altitude that could
shape the distribution of identified plant
communities.
168
Table 1. List of plant species with their family, botanical name and habit.
S.No
FAMILY
SPECIES
1.
Malvaceae
Abutilion bidentatum (Hochst.)A. Rich.
2.
Malvaceae
Abutilion fruticosum Guill. & Perr.
3.
Malvaceae
Abutilion longicuspe Hochst. ex A.Rich
4.
Malvaceae
Abutilon anglosomaliae Cufod
5.
Malvaceae
Abutilon figarianum Webb
6.
Malvaceae
Abutilon ramosum Guill. & Perr.
7.
Fabaceae
Acacia albida Del.
8.
Fabaceae
Acacia brevispica Harms
9.
Fabaceae
Acacia dolichocephala Harms
10.
Fabaceae
Acacia drepanalobium Harms ex Sjosted
11.
Fabaceae
Acacia lahai Steud. & Hochst.ex Benth.
12.
Fabaceae
Acacia mellifera (Vahl) Benth.
13.
Fabaceae
Acacia nilotica (L.) Willd. ex Del.
14.
Fabaceae
Acacia oerferta (Forssk.) Schweinf.
15.
Fabaceae
Acacia polyacantha Willd.
16.
Fabaceae
Acacia senegal (L.) Willd.
17.
Fabaceae
Acacia seyal Del.
18.
Fabaceae
Acacia tortilis (Forssk.) Hayne
19.
Euphorbiaceae
Acalypha fruticosa Forssk.
20.
Amaranthaceae
Achyranthes aspera L.
21.
Poaceae
Acrachne racemosa (Roem. And Schult.)Ohwi.
22.
Actinopteridaceae
Actiniopteris dimorpha Pic. Serm
23.
Apocynaceae
Adenium obesum (Forssk.) Roem. & Schult.
24.
Amaranthaceae
Aerva javanica (Burm.f.) Schultes
25.
Amaranthaceae
Aerva lanata (L.) Juss.ex.J.A.Schuletes
26.
Agavaceae
Agave sisalana Perrine ex Engl.
27.
Sapindaceae
Allophyllus rubifolius (Hochst.ex A.Rich).Engl.
28.
Aloaceae
Aloe otallensis Baker
29.
Aloaceae
Aloe rugosifolia Gilbert & Sebsebe
30.
Fabaceae
Alysicarpus glumaceus (Vahl) DC
31.
Amaranthaceae
Amaranthus spinosus L.
32.
Combretaceae
Anogeissus leiocarpa (A. DC.) Guill. & Perr.
33.
Rubiaceae
Anthospermum herbaceum L. f.
34.
Poaceae
Aristida kenyensis Henr.
35.
Asteraceae
Aspilia africana (Pers.) Adams
36.
Balanitaceae
Balanites aegyptiaca (L.) Del.
37.
Balanitaceae
Balanites rotundifolia (Van Tieghem) Blat.
38.
Acanthaceae
Barleria acanthoides Vahl
39.
Acanthaceae
Barleria eranthemoides R. Br. ex C.B. Clarke
40.
Acanthaceae
Barleria steudneri C.B. Clarke
41.
Rhmnaceae
Berchemia discolor (Klotzsch) Hemsl.
42.
Asteraceae
Bidens pilosa L.
43.
Poaceae
Brachiaria serrata (Thunb.) Stapf
44.
Euphorbiaceae
Bridelia micrantha (Hochst.) Baill.
45.
Capparidaceae
Cadaba farinosa Forssk.
46.
Capparidaceae
Cadaba rotundifolia Forssk.
Copyright © Journal of the Drylands 2010
ISSN 1817-3322
HABIT
Shrub
Herb
Shrub
Shrub
Herb
Herb
Tree
Shrub
Tree
Shrub
Shrub
Shrub
Tree
Shrub
Tree
Shrub
Tree
Tree
Shrub
Herb
Herb
Herb
Shrub
Shrub
Herb
Herb
Tree
Herb
Herb
Herb
Herb
Tree
Herb
Herb
Herb
Tree
Shrub
Shrub
Shrub
Herb
Tree
Herb
Herb
Shrub
Shrub
Shrub
S.No
47.
48.
49.
50.
51.
52.
53.
54.
55.
56.
57.
58.
59.
60.
61.
62.
63.
64.
65.
66.
67.
68.
69.
70.
71.
72.
73.
74.
75.
76.
77.
78.
79.
80.
81.
82.
83.
84.
85.
86.
87.
88.
89.
90.
91.
92.
FAMILY
Capparidaceae
Capparidaceae
Capparidaceae
Capparidaceae
Capparidaceae
Capparidaceae
Apocynaceae
Malpighiaceae
Ulmaceae
Ulmaceae
Ulmaceae
Poaceae
Menespermaceae
Menespermaceae
Vitaceae
Vitaceae
Capparidaceae
Araceae
Combretaceae
Combretaceae
Combretaceae
Combretaceae
Combretaceae
Combretaceae
Burseraceae
Burseraceae
Burseraceae
Burseraceae
Boraginaceae
Boraginaceae
Capparidaceae
Asteraceae
Amaryllidaceae
Amaryllidaceae
Fabaceae
Euphorbiaceae
Cucurbitaceae
Poaceae
Poaceae
Poaceae
Cyperaceae
Poaceae
Fabaceae
Fabaceae
Fabaceae
Amaranthaceae
169
SPECIES
Cadaba sp.
Capparis cartilaginea Decne.
Capparis erythrocapos Isert
Capparis fascicularis DC
Capparis sepiaria L.
Capparis tomentosa Lam.
Carissa spinarum Forssk. Vahl.
Caucanthus auriculatus (Radlk.) Niedenzu
Celtis africana Burm. f.
Celtis toka (Forssk.) Hepper & Wood
Celtis zenkeri Engl.
Cenchrus ciliaris L.
Cissampelos mucronata A. Rich.
Cissampelos pareira L.
Cissus quadrangularis L.
Cissus rotundifolia (Forssk.) Vahl
Cleome hirta (Klotzsch) Oliv.
Colocasia rueppellii Sch.Bip
Combretum collinum Fresen
Combretum hereroense Schinz.
Combretum molle R.Br.ex G.Don
Combretum panculatum Vent.
Combretum sp.1
Combretum sp.2
Commiphora africana (A.Rich) Engl.
Commiphora albiflora Engl.
Commiphora bruceae Chiov.
Commiphora terebinthina Vollesen
Cordia africana Lam.
Cordia monoica Roxb.
Crateva adansonii DC
Crepis rueppellii Sch. Bip.
Crinum abyssincum Hochest.ex A.Rich
Crinum macowanii Baker
Crotolaria incana L.
Croton macrostachyus Del.
Cucumis dipsaceus Eherenb.ex.Spach.
Cymbopogon commutatus (Steud.) Stapf
Cynodon dactylon (L.) Pers.
Cynodon plectostachyus (K. Schum.) Pilg.
Cyperus niveus Retz.
Dactyloctenium aegypticum (L.) Willd.
Dalbergia lacteal Vatke
Dalbergia microphylla Chiov
Dicrostachys cinerea (L.)Wight and Arn.
Digera muricata (L.) Mart.
HABIT
Shrub
Shrub
Shrub
Shrub
Shrub
Shrub
Shrub
Liana
Tree
Tree
Tree
Herb
Liana
Liana
Liana
Liana
Herb
Herb
Tree
Shrub
Tree
Liana
Shrub
Shrub
Tree
Shrub
Shrub
Tree
Tree
Shrub
Shrub
Herb
Herb
Herb
Herb
Tree
Herb
Herb
Herb
Herb
Herb
Herb
Shrub
Shrub
Shrub
Herb
Table 1. Continued
S.No
FAMILY
93.
Poaceae
94.
Poaceae
95.
Ebenaceae
96.
Flacourtiaceae
97.
Acanthaceae
98.
Poaceae
99.
Boraginaceae
100. Pontederiaceae
101. Celastraceae
102. Poaceae
103. Poaceae
104. Poaceae
105. Poaceae
106. Euphorbiaceae
107. Ebenaceae
108. Ebenaceae
109. Euphorbiaceae
110. Euphorbiaceae
111. Euphorbiaceae
112. Euphorbiaceae
113. Moraceae
114. Moraceae
115. Euphorbiaceae
116. Guttiferae
117. Tiliaceae
118. Tiliaceae
119. Tiliaceae
120. Tiliaceae
121. Tiliaceae
122. Tiliaceae
123. Simaroubaceae
124. Boraginaceae
125. Boraginaceae
126. Poaceae
127. Malvaceae
128. Fabaceae
129. Malvaceae
130. Malvaceae
131. Phytolaccaceae
132. Celastraceae
133. Fabaceae
134. Fabaceae
135. Fabaceae
136. Convolvulaceae
137. Acanthaceae
138. Acanthaceae
Copyright © Journal of the Drylands 2010
ISSN 1817-3322
SPECIES
Digitaria abyssinica (Hochst. ex A. Rich.) Stapf
Digitaria velutina (Forssk.) P. Beauv.
Diospyros abyssinica (Hiern) F.White
Dovyalis abyssinica (A. Rich.) Warb.
Dyschoriste multicaulis (A. Rich.) O. Kuntze
Echinocloa pyramidals (Lam.) Hitchc. & Chase
Ehretia cymosa Thonn.
Eichornia crassipes (Mart.)Solms in A.DC
Elaeodendron buchananii (Loes.) Loes.
Eragrostis ciliaris (L.) R. Br.
Eragrostis japonica (Thunb.)Trin.
Eragrostis paniciformis (A. Br.) Steud.
Eragrostis sp.
Erythrococca trichogyne (Muell. Arg.) Prain
Euclea divinorum Hiern
Euclea racemosa Murr.
Euphorbia indica Lam.
Euphorbia inaequilatera Sond.
Euphorbia polyacantha Boiss.
Euphorbia tirucalli L.
Ficus sycamorus L.
Ficus vasta Forssk.
Flueggea virosa (Willd.) Voigt
Garcinia livingstonia Oliver
Grewia bicolor Juss.
Grewia ferruginea Hochst. ex A. Rich
Grewia mollis A. Juss.
Grewia tenax (Forssk.) Fiori
Grewia velutina (Forssk.) Vahl
Grewia villosa Willd.
Harrisonia abyssinica Oliv.
Heliotropium rariflorum Stocks
Heliotropium somalense Vatke
Heteropogon contortus (L.) Roem. & Schult.
Hibiscus aponeureus Sprague & Hutch.
Hibiscus cannabinus L.
Hibiscus micranthus L. f.
Hibiscus palmatus Forssk.
Hileria latifolia (Lam.) H.Walter.
Hippocratea africana (Wild) Loes.
Indigofera arrecta Hochst. ex A. Rich.
Indigofera schimperi Jaub. & Spach.
Indigofera sp.
Ipomoea aquatica Forssk.
Isoglossa laxa Oliv.
Justicia anagalloides (Nees) T. Anders.
HABIT
Herb
Herb
Tree
Shrub
Herb
Herb
Shrub
Herb
Shrub
Herb
Herb
Herb
Herb
Shrub
Shrub
Shrub
Herb
Herb
Shrub
Tree
Tree
Tree
Shrub
Shrub
Shrub
Shrub
Shrub
Shrub
Shrub
Shrub
Shrub
Herb
Herb
Herb
Herb
Herb
Herb
Herb
Herb
Liana
Herb
Shrub
Herb
Herb
Herb
Herb
S.No
139.
140.
141.
142.
143.
144.
145.
146.
147.
148.
149.
150.
151.
152.
153.
154.
155.
156.
157.
158.
159.
160.
161.
162.
163.
164.
165.
166.
167.
168.
169.
170.
171.
172.
173.
174.
175.
176.
177.
178.
179.
180.
181.
182.
183.
184.
FAMILY
Acanthaceae
Acanthaceae
Crassulaceae
Crassulaceae
Bignoniaceae
Asteraceae
Verbenaceae
Verbenaceae
Lamiaceae
Poaceae
Capparidaceae
Capparidaceae
Capparidaceae
Capparidaceae
Capparidaceae
Sapotaceae
Celastraceae
Celastraceae
Asteraceae
Molluginaceae
Acanthaceae
Moringaceae
Cactaceae
Anacardiaceae
Asclepiadaceae
Poaceae
Sapindaceae
Asteraceae
Poaceae
Poaceae
Asclepiadaceae
Euphorbiaceae
Euphorbiaceae
Rosaceae
Amaranthaceae
Anacardiaceae
Fabaceae
Fabaceae
Euphorbiaceae
Poaceae
Draceanaceae
Convolvulaceae
Poaceae
Malvaceae
Malvaceae
Solanaceae
SPECIES
Justicia caerulea Forssk.
Justicia heterocarpa T. Anders.
Kalanchoe densiflora Rolfe
Kalanchoe sp.
Kigelia africana (Lam.) Benth.
Kleinia odora (Forssk.) DC.
Lantana camara L.
Lantana virburnoides (Forssk} Vahl
Leucas abyssinica (Benth.) Briq.
Loudetia flavida (Stapf) C.E. Hubb
Maerua aethiopica (Fenzl.) Oliv.
Maerua angolensis DC.
Maerua crassifolia Forssk.
Maerua oblongifolia (Forssk.) A. Rich.
Maerua triphylla A.Rich
Manilkara butugi Chiov.
Maytenus arbutifolia (A.Rich) Wilczek
Maytenus undata (Thunb.) Blakelock
Microglossa pyrifolia (Lam.) O. Kuntze
Mollugo nudicaulis Lam.
Monechma debile (Forssk.) Nees
Moringa stenopetala (Bak.f.) Cuf.
Opuntia ficus-indica (L.) Miller
Ozoroa insignis Del.
Pachycymbium gilbertii (Plowes) M.G.Gilbert
Panicum maximum Jacq.
Pappea capensis Eckl. & Zeyh.
Parthenium hysterophorus L.
Paspalum sp
Pennisetum mezianum Leeke
Pentatropis nivalis (J.F.Gmel) D.V.Field & J.R.I.Wood
Phyllanthus maderaspatensis L.
Phyllanthus pseudoniruri Muell. Arg.
Prunus africana (Hook. f.) Kalkm.
Puplia lappacea (L.) A.Juss.
Rhus natalensis Bern. ex Krausse
Rhynchosia malacophylla (Spreng.)Boj
Rhynchosia minima (L.) DC.
Ricinus communi L.
Rostaria cristata (L.) Tzvelev.
Sansevieria forskaoliana (Schult.f.) Hepper & Wood
Seddera Arabica (Forssk.) Choisy
Setaria acromelaena (Hochst.) Th. Dur. & Schinz
Sida ovata Forssk.
Sida schimperiana Hochst. ex A. Rich.
Solanum anguivi Lam.
170
HABIT
Herb
Herb
Herb
Herb
Tree
Shrub
Shrub
Shrub
Shrub
Herb
Shrub
Shrub
Shrub
Shrub
Shrub
Tree
Shrub
Shrub
Shrub
Herb
Herb
Tree
Shrub
Shrub
Herb
Herb
Tree
Herb
Herb
Herb
Herbacious Climber
Herb
Herb
Tree
Herb
Shrub
Herb
Herbacious Climber
Shrub
Herb
Herb
Herb
Herb
Herb
Shrub
Shrub
Table 1. Continued
S.No
FAMILY
185.
Solanaceae
186.
Poaceae
187.
Poaceae
188.
Apiaceae
189.
Sterculiaceae
190.
Myrtaceae
191.
Fabaceae
192.
Rutaceae
193.
Fabaceae
194.
Fabaceae
195.
Combretaceae
196.
Combretaceae
197.
Combretaceae
198.
Ulmaceae
199.
Meliaceae
200.
Moraceae
201.
Asteraceae
202.
Asteraceae
203.
Asteraceae
204.
Asteraceae
205.
Asteraceae
206.
Olacaceae
207.
Rhmnaceae
208.
Rhmnaceae
SPECIES
Solanum incanum L.
Sporobulos africanus (Poir.) Robyns & Tournay
Sporobulos spicatus (Vahl) Kunth
Steganotaenia araliacea Hochst. ex A. Rich.
Sterculia setigera Del.
Syzygium guineense (Willd.) DC.
Tamarindus indica L.
Teclea nobilis Del.
Tephrosia fulvinervis Hochest. ex.A. Rich.
Tephrosia linearis (Willd.) Pers.
Terminalia brownii Fresen.
Terminalia schimperiana Hochst.
Terminalia sp.
Trema orientalis (L.) Blume
Trichilia dregeana Sond.
Trilepisium madagascariense DC.
Vernonia adoensis Sch.Bip.ex Walp
Vernonia cinerascens Sch. Bip.
Vernonia hochsterreru Sch.Bip.ex Walp
Vernonia hymenolepis A.Rich
Vernonia uncinata Oliv. & Hiern
Ximenia americana L.
Ziziphus mucronata Willd.
Ziziphus spina-christi (L.) Desf.
HABIT
Shrub
Herb
Herb
Tree
Tree
Tree
Tree
Shrub
Shrub
Herb
Tree
Tree
Shrub
Tree
Tree
Tree
Shrub
Shrub
Shrub
Shrub
Herb
Tree
Tree
Tree
Table 2. Indicator values (% of perfect indication) of some species for each group (five groups) and the
Monte Carlo test (p*) of significance observed for species. These values were obtained by combining the
relative abundance and relative frequencies of species
Species
Acrachne racemosa
Cleome hirta
Crateva adansonii
Rhus natalensis
Balanites aegyptiaca
Capparis cartilaginea
Dovyalis abyssinica
Aristida kenyensis
Cenchrus ciliaris
Tamarindus indica
Acacia mellifera
Acacia lahai
Microglossa pyrifolia
Justicia heterocarpa
Syzygium guineense
Capparis sepiaria
Adenium obesum
Panicum maximum
Cadaba farinosa
Acacia brevispica
Ziziphus spina-christi
Acalypha fruticosa
Flueggea virosa
Erythrococca trichogyne
Hibiscus cannabinus
Elaeodendron buchananii
Mollugo nudicaulis
Manilkara butugi
Acacia albida
Maytenus undata
Pachycymbium gilbertii
Dalbergia microphylla
Dactyloctenium aegypticum
Lantana camara
Barleria acanthoides
Monechma debile
Terminalia brownii
Copyright © Journal of the Drylands 2010
ISSN 1817-3322
Number of plots
1
11
Community
2
3
16
24
4
11
5
8
95
89
0
0
1
1
0
0
0
1
14
7
4
0
3
0
16
9
2
3
1
0
9
5
0
12
6
0
2
0
12
0
0
7
2
0
1
0
0
81
81
74
0
1
1
41
0
0
0
0
40
1
7
0
1
0
42
46
6
3
0
0
9
10
9
45
2
1
7
1
0
0
1
5
0
1
0
1
0
0
18
68
47
0
0
1
6
0
0
0
2
1
0
2
1
0
5
0
0
7
4
0
2
27
3
0
22
0
12
2
36
1
0
0
0
1
2
5
0
0
88
83
64
59
58
57
55
54
52
52
49
46
46
36
28
28
25
25
25
24
24
23
22
20
18
18
18
17
0
2
0
15
20
79
70
14
2
1
2
0
0
1
3
4
3
1
29
0
0
0
0
4
0
0
0
2
1
6
2
3
27
2
0
0
1
p*
0.0062
0.0052
0.0002
0.0002
0.0022
0.0032
0.0032
0.0012
0.0072
0.0012
0.0002
0.5711
0.3002
0.0342
0.0062
0.0062
0.2802
0.4313
0.0042
0.0002
0.0354
0.6543
0.1002
0.0092
0.0122
0.0140
0.0412
0.0118
0.0034
0.5002
0.0012
0.0018
0.0466
0.0842
0.041
0.0262
0.0602
171
Figure 3. Dendrogram output of the cluster analysis showing the five communities and respective plots
I. Acrachne racemosa - Cleome hirta type
The community type distributed between the
altitudinal ranges of 1210 m and 1300 m above
sea level. In this community, A. tortilis is the
dominant species in the tree layer, while D.
abyssinica is the characteristic species in the tree
layer. A. nilotica, G. villosa and A. oerferta are the
major browsable in the woody layer. A. racemosa
and C. hirta is dominant species in the field layer.
Other herbaceous dominating the field layer
include Actiniopteris dimorpha and Justicia
caerulea.
II. Crateva adansonii - Rhus natalensis–
Balanites aegyptiaca type
The community type distributed between the
altitudinal ranges of 1270 m and 1350 masl. In
this community B. aegyptiaca, A. tortilis, A.
leiocarpa and A. albida are the major browse
species in the tree layer. Other species in the tree
layer include X. americana, Z. mucronata and Z.
spina-christi are also preferable browse species.
Kigelia africana is the characteristic species in the
tree layer. Crateva adansonii, Rhus natalensis and
A. brevispica is also browsable species in the
shrub layer. In this type, Cissus quadrangularis
occurs in dense clumps. Other species dominating
the field layer include Cenchrus ciliaris, D.
abyssinica and J. heterocarpa.
III.Capparis cartilaginea – Dovyalis abyssinica
type
The community type distributed between the
altitudinal ranges of 1150 m and 1380 masl. In
this community, A. seyal and C. molle are the
major browse species in the tree layer. C.
cartilaginea, D. abyssinica is also the browsable
species in the shrub layer. In this type, A. senegal,
Copyright © Journal of the Drylands 2010
ISSN 1817-3322
Ozoroa insignis and Harrisonia abyssinica is the
dominant species in the field layer. Other species
in the field layer preferable for grazing include
Heteropogon contortus
and
Cymbopogon
commutatus.
IV. Aristida keyensis – Cenchrus ciliaris type
The community type distributed between the
altitudinal ranges of 1300 m and 1440 masl. In
this community, C. erythrocapos, D. abyssinica
and M. undata are the major browse species in the
shrub layer. T. brownii and E. tirucalli is also the
browsable in the tree layer. In this type, C.
quadrangularis and C. rotundifolia is the
dominant woody climber species in the field layer.
Other species preferred for grazing in the field
layer include A. keyensis, C. ciliaris, D. velutina,
Abutilon figarianum, Indigofera arrecta and C.
commutatus.
V.Tamarindus indica – Acacia mellifera type
The community type distributed between the
altitudinal ranges of 1190 m and 1225 masl. In
this community, S. guineense, T. indica and A.
lahai are the major browse species in the tree
layer. Z. spina-christi is also the preferable browse
in the tree layer. In this type, Adenium obesum, A.
brevispica, Acalypha fruticosa, C. farinosa, C.
sepiaria and Microglossa pyrifolia is the
dominant species in the field layer. Other species
in the field layer include J. heterocarpa and
Panicum maximum are preferable for grazers.
According to (Clements, 1916; 1992 as cited
in Kent and Coker, 1992), plant community had
seen as clearly recognizable and definable entities
which repeated themselves with great regularity
over a given region of the earth’s surface. This
study assessed whether there were or not a
172
repetition of these five community types of NNP
with other previously reported community types
from other dryland parts of Ethiopia. And it was
found that the community types of NNP were
completely different from community types so far
discovered in other dryland parts of the country.
For instance, Gemedo, et al., (2005) was
identified eight plant communities: from Borana
lowland. Haileab, et al., (2006) also identified
nine community types from the Rift Valley area.
Even from the past research that have done in
NNP by Tamrat, (2001) in the plain grass land of
the six community types.
This may suggest that NNP is an isolated
system of its own because of the past and present
interactions of local biotic and abiotic factors such
as temperature, edaphic, rainfall, anthropogenic,
faunal, topographic and geographic factors.
However, community type IV of this study A.
keyensis – C. ciliaris showed similarity with two
communities out of the six community types
identified by Tamrat, (2001). C. ciliaris – B.
aegyptiaca type according to this report, B.
aegyptiaca and A. tortilis were the dominant
species in the tree layer similarly, of C. adansonii
– R. natalensis– B. aegyptiaca type (Community
type II) B. aegyptiaca and A. tortilis were the
dominant species in the tree layer
This similarity finding further ratifies the
earlier suggestion in that in both studies there is
relative similarity except the sites where plots
taken for data collection and time gap between the
two studies made them a bit similar in their
emerged plant associations as compared to Borena
and Rift Valley areas, which are not relatively
located in proximity with NNP. Even from the
two sites the study in Borena has relatively a bit
similar species dominating in some community
types. This implied that the further we went to the
closer geographical location, the more probability
we would have in finding similar associations of
plant communities. The complex interaction of
environmental variables along spatial gradients
will form a complex environmental gradient that
characterizes the nature and distribution of
communities along landscapes (Begon et al.,
1996; Urban et al., 2000; Tuomisto et al., 2003).
Communities 1, 2, 3, 4 and 5 were found to
accommodate about 45, 44, 58, 34, and 28
ethnomedicinal plant species, respectively
(Ermias, 2005; Haile et al., 2007; 2008; Tinsae,
2009). Altitude has been investigated in a number
of studies (e.g., Sebsebe, 1988; Tamrat, 1993;
Miehe and Miehe, 1994; Demel, 1995b; Abate,
2003; Ermias, 2005; Haile et al., 2008a; Tadesse
et al., 2008) as one of the major environmental
gradients that could shape the species composition
and distribution of plant communities. This
environmental variable seems to have significant
contribution in the current study area in
Copyright © Journal of the Drylands 2010
ISSN 1817-3322
determining plant community compositions and
zones despite the presence of overlaps with some
community types.
Similarity, diversity and evenness of
community types
Generally, as seen from Table 3 all five
community types showed good diversity in
Shannon-Wiener index. There were also fair
evenness and small dominance in all types. Owing
to their difference in numbers of quadrants,
species richness and diversity of the five
communities were different. The highest species
richness was observed in community three also
community three is more diverse and community
four is the least diverse but the evenness is
opposite and community four is more even and
community three is the least (Table 3).
Table 3. Species richness, dominance, diversity and
evenness of five community types
Communities
C1
C2
C3
C4
C5
Species
Richness
56
63
87
49
58
Dominance
D
0.03
0.04
0.03
0.04
0.03
Shannon
H'
3.65
3.59
3.86
3.53
3.68
Evenness
e^/S
0.69
0.57
0.54
0.7
0.69
The Shannon diversity index of Nechisar
National Park was found to be 3.66 reflecting
good diversity. The 208 species encountered in
the area were distributed evenly with the Shannon
evenness value of 0.64 and small dominancy
(0.03). Moreover, the number of species across
quadrants showed that species richness across
quadrants was good with 34 mean numbers of
species. In other words, there was a good share of
diversity among all quadrants. According to Kent
and Coker (1992), the Shannon-Weiner diversity
index normally varies between 1.5 and 3.5 and
rarely exceeds 4.5. And low Shannon evenness is
an indication of the existence of unbalanced
distribution of the individuals of species
encountered at a given study areas. However, it
can be said that the area is with good diversity and
more or less even representation of individuals of
all species encountered in the studied quadrants.
Density, diameter, height and population
structure of woody species.
Species-abundance measures are ways of
expressing not only the relative richness but also
evenness and thereby assessing diversity (Barnes
et al., 1998). A total of 1976 individuals of woody
plants (886.78 individuals ha-1) of woody plants
were encountered. A. leiocarpa, Z. spina-christi,
Z. mucronata and B. aegyptiaca were the most
abundant species while species like K. africana,
C. africana and T. orientalis were rarely recorded
in this regard. This densities are low compared to
173
some other studies in different forests of Ethiopia,
for example Kimphee Forest (3059 stems ha-1)
(Feyera and Demel, 2003), Masha-Andercha
Forest (1709) stems ha-1) (Kumulachew and Taye,
2003) and Dindin Forest (1750 stems ha-1) (Simon
and Girma, 2004). This could be attributed to
variation in landscape topographic gradients as
well as habitat qualities linked to ecological
requirements of component tree and shrub species
in the respective forests. The density of trees and
shrubs at DBH > 10cm was 572 individuals ha-1
accounting for 64.5 % of the total density of trees
and shrubs and that’s of DBH > 20cm was 342
individuals ha-1 (Table 4). This was actually
greater than density of tree species of many
forests in Ethiopia as seen in the Table 4. The
ratio of density at DBH class >10 cm to density at
DBH class >20cm was 1.67. These comparisons
indicated that in the park the small-sized
individuals are more dominant. The major reason
for this is selective cutting of medium sized
individuals for a variety of purposes. Similar
conditions are reported from other forests as seen
in the table and the ratio is relatively small in
Dodola and Highest in Chillimo Forest (Table 4).
Table 4. Comparison of tree densities with DBH between 10 and 20 cm (a) and tree density with DBH >
20 cm (b) From NNP with 11 other forests in Ethiopia
Forests
Menagesha
Chillimo
Donkoro
Masha Andaracha
Dodola
Dindin
Magada
Mena Angetu
Gura ferda
Adelle
Boditi
Alata Bolale
NNP
a
484
638
526
385.7
521
437
608
292
500
413
256
365
572
Density
B
208
250
285
160.5
351
219
332
139
263
164
114
219
342
Ratio
a/b
2.33
2.55
1.85
2.40
1.48
2.00
1.83
2.10
1.90
2.52
2.25
1.67
1.67
Ten woody species with the highest density
were Z. spina-christi (116.42 ind. ha-1), R.
natalensis (66.48 ind. ha-1), D. abyssinica (48.29
ind. ha-1), X. americana (46.18 ind. ha-1), A. seyal
(39.65 ind. ha-1), A. brevispica (30.69 ind. ha-1),
Z. mucronata (30.32 ind. ha-1), A. tortilis (30.24
ind. ha-1), A. leiocarpa (29.94 ind. ha-1), and B.
aegyptiaca (29.68 ind. ha-1).
The general pattern of diameter classes’
distribution pattern resulted in a reverse-J-shape
(Fig. 4). It revealed as there was a very high
decrease in density of diameter greater than 70
cm. The density of woody individuals generally
decreased with increasing diameter classes and
78% of the total individuals are less than 30 cm.
(Fig. 4). Similarly, the density distribution of
woody individuals in different height classes also
showed a similar pattern with diameter classes a
reverse-J-shape (Fig. 5). There was a very high
decrease in density of species greater than 12 m.
Generally, it showed a decrease in density with
increasing height classes (Fig. 5). According to
the reports of Feyera et al. (2007) and Getachew
and Abiyot, (2006), an Inverted J-shape height
class distribution pattern was considered as a
normal type of distribution indicating continuous
or good regeneration revealed by stable
population. The population structure of selected
species from Nechisar National Park fell into one
of four general diameter class distribution
Copyright © Journal of the Drylands 2010
ISSN 1817-3322
Sources
Tamrat Bekele, 1994
Tamrat Bekele, 1994
Abate Ayalew et al., 2006
Kumelachew Yeshtela and Taye Bekele, 2003
Kitessa Hundera, 2007
Simon Shibru and Girma Balcha, 2004
Genene Bekele, 2005
Ermias Lulekal et al., 2008
Dereje Denu, 2007
Haile Yineger et al., 2008a
Haile Yineger et al., 2008a
Woldeyohannes Enkossa, 2008
Present study
patterns. These are: 1) Bell-shape, (Gaussian type)
2) Inverted-J-shape, 3) J-shape, 4) Interrupted Ushape.
Information on population structure of a tree
species indicates the history of the past
disturbance to that species and the environment
and hence, used to forecast the future trend of the
population of that particular species (Tamrat,
1994; Demel, 1997). The frequency distribution of
individuals in the various diameter and height
class is not uniform (Figs. 4 and 5) as the DBH
size increases, the number of individuals gradually
decreases and showed a slight increase in the last
class (Fig. 4). Similar trend is seen in frequency
distribution of height of woody species (Fig. 5).
Figure 4. Diameter class frequency distribution
of woody species in Nechisar National Park
174
Figure 5. Height class (m) distribution of
woody species in Nechisar National Park
According to previous studies made by
Silvertown (1982), Silvertown and Doust, (1993),
Tamrat, (1993), Mekuria et al. (1999), Alemnew,
(2001), Alemayehu, (2002), Getachew et al.
(2002), Ensermu and Teshome, (2008) and Haile
et al., ( 2008a). B. aegyptiaca was depicted in
Bell-shape (Gaussian type) distribution pattern.
This is the reflection of a discontinuous or
irregular recruitment. This species is one of the
most economically important species. This might
be one of the most important reasons that made
the species retard from its normal recruitment
status. Five species shows this pattern: S.
guineense, T. orientalis, M. stenopetala, F.
sycamorus and D. abyssinica. This pattern
indicates a poor reproduction, but we can only
speculate about the reason for the decline in the
number of big sized trees. A reverse J-shape
distribution pattern was considered as an
indication of stable population status or good
regeneration status but a bad recruitment.
However, both cumulative diameter class
distribution of individual woody plants and
selected species were resulted in patterns showing
a good regeneration profiles but a bad recruitment.
The cumulative one showed a nearly reverse Jshape with a very high decrease in density of
diameter greater than 20 cm. This revelation tells
us that as there had been a selective removal of
medium to big sized diameter class individuals
either by local dwellers around the Park for some
purpose (e.g. for fencing and fuel wood), or by
livestock (trampling or browsing), or may be other
biotic impairments like termite attack.
In most cases, this diameter class is the most
susceptible and palatable age of individuals and
this may be the reason behind that made
individuals unable to cope up with any
disturbance encountered. A. leiocarpa, Z. spinachristi and A. seyal were depicted in an Inverse Jshape. A. leiocarpa was revealed a very high
decrease in density at diameter class five and six,
and totally miss diameter class seven while Z.
spina-christi and A. seyal decreases continuously
towards the higher DBH class without any miss.
This may due to some reasons that explained for
the case of cumulative diameter class distribution.
Copyright © Journal of the Drylands 2010
ISSN 1817-3322
S. setigera was fallen in J-shape distribution
pattern which is considered to be a reflection of a
severe limitation on the regeneration for some
reason (Peters, 1996). This study noted that S.
setigera was one of the most important
multipurpose tree species used for fodder,
construction, fence and others; In addition, the
peels of this species used as chewing gum by kids.
These may be some of the reasons that made the
species to be such a severely hampered
regeneration status. Other species showing such
pattern are T. indica, T. brownii, X. americana and
C. farinosa. These species were, thus, with the
poorest regeneration status than the others. This
might have happened may be also due to the poor
reproductive capacities of its old individuals.
C. africana showed an Interrupted U-shape with
complete absent of individuals in diameter class
five and six. The frequencies are high in the
lowest and highest DBH classes with more or less
very low in the intermediate classes resulting in a
U- shape. This pattern vividly shows that selective
cutting and removal of medium sized individuals
have taken place. Only one species C. africana
belongs to this type.
Basal area, frequency and importance value
index (IVI)
The basal area of all woody species was 49.45m2
per hectare. Basal areas of NNP are less than
reported forests in the country, for example, WofWasha Forest (about 102 m2ha-1), Jibat Forest
(about 50 m2ha-1) (Tamrat, 1993), Mana Angetu
Forest (94 m2ha-1) (Ermias, 2005) and it is greater
than Denkoro Forest (45 m2ha-1) (Abate, 2003) ,
Chilimo Forest (about 30 m2ha-1) (Tamrat, 1993),
Adelle Forest (about 26 m2ha-1) and Boditi Forest
(about 23 m2ha-1) (Haile et al., 2008a). Basal
area provides the measure of the relative
importance of the species than simple stem count,
species with largest contribution in dominance
value could be considered as the most important
species in the study vegetation. Otherwise, in
most cases shrubs could be the dominant species
if only we consider density as a measure to
indicate the overall dominance of the species
(Simon and Girma, 2004; Adefires, 2006).
The following species made the largest
contribution to the basal area: B. aegyptiaca
(13.23 %), A. leiocarpa (11.02 %), S. setigera
(10.64 %), B. rotundifolia (9.14 %), C. africana
(8.74 %), C. africana (7.28%), F. sycamores
(7.28%), D. cinerea (6.53%), C. molle (6.47%),
M. stenopetala (6.31%) and C. collinum (4.27%).
But the other remaining species contributed to
only 9.1 % (Table 6). This implies that the above
mentioned eleven species are the most
ecologically important woody species in NNP.
Table 5 summarizes the top woody plants with
highest frequency in the park. The five most
175
frequent woody plants were A. seyal, Z.
mucronata, A. leiocarpa, B. aegyptiaca and Z.
spina-christi. Frequency reflects the pattern of
distribution and gives an approximate indication
of the heterogeneity of a stand (Lamprecht, 1989;
Haileab et al., 2006).
Table 5. Frequency (%) of the most frequent woody species in Nechisar National Park
Species
Acacia seyal
Ziziphus mucronata
Anogeissus leiocarpa
Balanites aegyptiaca
Ziziphus spina-christi
Ximenia americana
Dovyalis abyssinica
Maytenus undata
Acacia brevispica
Terminalia brownii
Cadaba farinosa
Euphorbia tirucalli
Cissus rotundifolia
Acacia albida
Rhus natalensis
Acacia tortilis
Syzygium guineense
Dicrostachys cinerea
Cordia africana
Acacia mellifera
Carissa spinarum
Tamarindus indica
Frequency (%)
55.71
55.71
52.86
45.71
44.29
42.86
40.00
40.00
32.86
27.14
25.71
25.71
24.29
21.43
21.43
20.00
20.00
17.14
12.86
11.43
11.43
10.00
Table 6. Importance value indices for woody species. First 10 IVI ranked species are labeled in bold
Frequency, RD – Relative Density, RDO - Relative Dominance, IVI- Importance Value Index
Species
Acacia albida
Acacia brevispica
Acacia mellifera
Acacia seyal
Acacia tortilis
Acalypha fruticosa
Anogeissus leiocarpa
Balanites aegyptiaca
Balanites rotundifolia
Bridelia micrantha
Cadaba farinosa
Cadaba rotundifolia
Capparis sepiaria
Carissa spinarum
Celtis africana
Cissus rotundifolia
Combretum collinum
Combretum molle
Commiphora africana
Cordia africana
Dalbergia lactea
Dicrostachys cinerea
Dovyalis abyssinica
Euphorbia tirucalli
Ficus sycamorus
Grewia bicolor
Maytenus undata
Moringa stenopetala
Rhus natalensis
Sterculia setigera
Syzygium guineense
Tamarindus indica
Terminalia brownii
Trema orientalis
Ximenia americana
Ziziphus mucronata
Ziziphus spina-christi
Total
Copyright © Journal of the Drylands 2010
ISSN 1817-3322
RF
2.96
4.54
1.58
7.69
2.76
0.59
7.30
6.31
0.39
0.59
3.55
0.99
1.18
1.58
0.99
3.35
0.59
0.20
0.20
1.78
0.99
2.37
5.52
3.55
0.79
0.20
5.52
0.39
2.96
0.59
2.76
1.38
3.75
0.39
5.92
7.69
6.11
100.00
RD
2.63
3.94
2.02
4.65
3.74
1.62
3.74
3.64
1.21
0.91
3.24
1.52
1.11
1.82
1.11
4.45
1.01
0.51
0.61
1.31
3.24
1.21
5.86
4.85
0.51
0.30
3.54
0.81
6.98
2.12
1.42
0.71
1.72
0.20
5.16
3.84
12.74
100.00
RDO
0.57
0.42
0.38
0.38
0.53
0.04
11.02
13.23
9.14
0.02
0.24
0.00
0.00
0.00
0.28
0.00
4.27
6.47
7.28
8.74
0.02
6.53
0.16
0.42
7.28
0.28
0.00
6.31
0.36
10.64
0.47
1.42
2.29
0.36
0.12
0.14
0.18
100.00
IVI
6.15
8.90
3.98
12.73
7.03
2.25
22.06
23.18
10.75
1.52
7.03
2.50
2.30
3.40
2.38
7.80
5.87
7.17
8.08
11.83
4.24
10.11
11.55
8.83
8.57
0.78
9.06
7.51
10.30
13.35
4.64
3.50
7.75
0.96
11.20
11.68
19.04
300.00
RF- Relative
IVI Rank
24
14
28
5
23
34
2
1
10
35
22
31
33
30
32
18
25
21
17
6
27
12
8
15
16
37
13
20
11
4
26
29
19
36
9
7
3
176
The result of frequency showed as there were
relatively fair presences of species in most of
quadrants. Scores of frequency were shared
among species, so the highest frequency became
low. In other words, it can be concluded as there
were fairly presences of many species in most of
the quadrants. These may be due to the fact that
these species might have a wide range of seed
dispersal mechanisms like by wind, wild animals,
birds and the like. According to Lamprecht
(1989), stands that yield more or less the same
Importance Value Index (IVI) for the
characteristic species indicate the existence of the
same or at least similar stand composition and
structure, site requirements and
comparable
dynamics among species but few species in NNP
shows this character clearly.
The relative ecological significance and / or
dominance of tree species in a forest ecosystem
could best be unraveled from analysis of IVI
values (Curtis and Mcintosh, 1950). Our results of
the calculation of IVI thus helped to identify the
dominant species in NNP (Table 5).
B.
aegyptiaca exhibited the highest IVI (about 23)
followed by A. leiocarpa and Z. spina-christi. G.
bicolor was the least dominant species with the
least relative dominance, relative density and
relative frequency.
CONCLUSIONS
The study concludes that
Urgent research and/or development action to
circumvent and address the problems faced by
especially by those species poorly scored and low
importance value index and reproductive biology
and regeneration ecology of poorly regenerating
and other species should be investigated in the
study and other similar areas in the country.

In line with the above recommendation,
research on seed viability of the problematic
species, their seed raining mechanisms and
problems,
their seedling establishment
mechanisms and problems, soil seed bank analysis
and other possible ways to identify specific
problems of the species that made them unable to
regenerate should be done.

Devising
environmentallyfriendly
strategy for effective scaling up of products and
productivity of those economically important tree
species growing in the Park. So that this in turn
will contribute to the conservation and sustainable
use of species in the area because management
strategies that focus on multiple-use conservation
approach is better.
ACKNOWLEDGMENTS
The Horn of Africa Regional Environment Center
and Network (HoA-REC/N) is gratefully
acknowledged for provision of financial support
through the Demand Driven Action Research
Copyright © Journal of the Drylands 2010
ISSN 1817-3322
(DDAR) program. Here, we would like to extend
our deepest thanks to members of National
Herbarium, Addis Ababa University for their
immense support throughout plant identification
time and the National Metrological Service
Agency was the source of the climate data without
which construction of the climadiagram would
have been impossible.
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