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Diversity, regeneration status, and population structures of gum and resin producing woody species in Borana, Southern Ethiopia

Authors:
  • Ethiopian Environment and Forest Research Institute, Addis Ababa, Ethiopia
  • Botswana University of Agriculture and Natural Resources (BUAN)
  • Targeted Technology Institute

Abstract and Figures

Severe drought and large-scale ecosystem degradation are the two major threats exacerbating livelihood vulnerability of the pastoral and agropastoral communities in Borana Zone, southern Ethiopia. Strategic integration and sustainable management of the vast gum and resin bearing dry forests offer significant socioeconomic and ecological opportunities to enhance adaptation of these communities to adverse climatic variability, while enhancing ecosystem resilience. This study was carried out to investigate the diversity, abundance, distribution, and population structure of gum and resin bearing species in Borana drylands. Surveys were carried out in two districts: Arero and Yabello. Seventy-five (20 × 20 m) quadrats were established at 500 m intervals along transects in seven localities. Forty-six woody species distributed in 16 families and 25 genera were encountered. Gum and resin producing species comprised about 42 and 61% of the total number of species, 49 and 68% of the density ha, and 73 and 84% of the total basal area at Arero and Yabello, respectively. Regeneration and diameter class distribution showed clear signs of healthy populations, except for a small number of species, which exhibited bell-shaped diameter class distribution patterns. The results revealed that Borana Zone hosts more diverse commercial gum and resin bearing species compared to the northern part of the country, where organized production and marketing of gum and resin are well developed, and other relatively similar places, such as Middle Rift Valley and the neighbouring Somali region in Ethiopia. Such diversity, abundance, and the overall positive regeneration status of most of the gum and resin bearing species in Borana make up a solid and healthy basis for promoting the sustainable management of woodland resources through organized production and commercialization of high value oleo-gum resins.
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Diversity, regeneration status, and
population structures of gum and resin
producing woody species in Borana,
Southern Ethiopia
Adefires Worku
a
, Demel Teketay
b
, Mulugeta Lemenih
c
&
Masresha Fetene
d
a
Ethiopian Institute of Agricultural Research, Forestry Research
Center, P.O. Box 30708, Addis Ababa, Ethiopia
b
Eco Mark Africa, African Eco-Labelling Mechanism Secretariat,
4th Floor, International House, P.O. Box 41607-00100, Nairobi,
Kenya
c
Wondo Genet College of Forestry and Natural Resources, P.O. Box
128, Shashemene, Ethiopia
d
Addis Ababa University, Science Faculty, Biology Department,
P.O. Box 31819, Addis Ababa, Ethiopia
Version of record first published: 23 Aug 2012
To cite this article: Adefires Worku, Demel Teketay, Mulugeta Lemenih & Masresha Fetene (2012):
Diversity, regeneration status, and population structures of gum and resin producing woody species
in Borana, Southern Ethiopia, Forests, Trees and Livelihoods, DOI:10.1080/14728028.2012.716993
To link to this article: http://dx.doi.org/10.1080/14728028.2012.716993
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Diversity, regeneration status, and population structures of gum and
resin producing woody species in Borana, Southern Ethiopia
Adefires Worku
a
, Demel Teketay
b
*, Mulugeta Lemenih
c
and Masresha Fetene
d
a
Ethiopian Institute of Agricultural Research, Forestry Research Center, P.O. Box 30708, Addis
Ababa, Ethiopia;
b
Eco Mark Africa, African Eco-Labelling Mechanism Secretariat, 4th Floor,
International House, P.O. Box 41607-00100, Nairobi, Kenya;
c
Wondo Genet College of Forestry
and Natural Resources, P.O. Box 128, Shashemene, Ethiopia;
d
Addis Ababa University, Science
Faculty, Biology Department, P.O. Box 31819, Addis Ababa, Ethiopia
Severe drought and large-scale ecosystem degradation are the two major threats
exacerbating livelihood vulnerability of the pastoral and agropastoral communities in
Borana Zone, southern Ethiopia. Strategic integration and sustainable management of
the vast gum and resin bearing dry forests offer significant socioeconomic and
ecological opportunities to enhance adaptation of these communities to adverse
climatic variability, while enhancing ecosystem resilience. This study was carried out
to investigate the diversity, abundance, distribution, and population structure of gum
and resin bearing species in Borana drylands. Surveys were carried out in two districts:
Arero and Yabello. Seventy-five (20 £ 20 m) quadrats were established at 500 m
intervals along transects in seven localities. Forty-six woody species distributed in 16
families and 25 genera were encountered. Gum and resin producing species comprised
about 42 and 61% of the total number of species, 49 and 68% of the density ha
-1
, and 73
and 84% of the total basal area at Arero and Yabello, respectively. Regeneration and
diameter class distribution showed clear signs of healthy populations, except for a
small number of species, which exhibited bell-shaped diameter class distribution
patterns. The results revealed that Borana Zone hosts more diverse commercial gum
and resin bearing species compared to the northern part of the country, where organized
production and marketing of gum and resin are well developed, and other relatively
similar places, such as Middle Rift Valley and the neighbouring Somali region in
Ethiopia. Such diversity, abundance, and the overall positive regeneration status of
most of the gum and resin bearing species in Borana make up a solid and healthy basis
for promoting the sustainable management of woodland resources through organized
production and commercialization of high value oleo-gum resins.
Keywords: dry woodland; density; frequency; dominance; Importance Value Index;
climate change adaptation
Introduction
Among the different agro-ecological zones existing in Ethiopia, drylands (super arid, arid,
semi-arid and dry, subhumid areas) cover the largest landmass proportion of the country,
estimated at over 70% (Georgis et al. 2010). Drylands in Ethiopia spread from 124 m below
sea level to 1,500 m above sea level, with rainfall ranging from 100 to 700 mm annually
(Georgis et al. 2010). These ecosystems host vast dry forest resources and are home for a
diverse flora and fauna and for unique endemic species (FAO 2010; Eshete et al. 2011).
ISSN 1472-8028 print/ISSN 2164-3075 online
q 2012 Taylor & Francis
http://dx.doi.org/10.1080/14728028.2012.716993
http://www.tandfonline.com
*Corresponding author. Email: dteketay@yahoo.com
Forests, Trees and Livelihoods
iFirst article, 2012, 1–12
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Dry forest resources are adapted to the pastoralist and agropastoralist land use systems and
to the harsh environment (Dalle et al. 2005). However, overgrazing, increasing population
pressure, and climate change have resulted in a severe degradation of these forests, making
them vulnerable to desertification (Teketay 2004 2005; Kassahun et al. 2008).
Dry forest and woodland resources in Ethiopia, as elsewhere in Africa, are important
components of the livelihoods of pastoralists and agropastoralists (Lemenih et al. 2003;
Woldeamanuel 2011; Worku et al. 2011). The complex socioeconomic and ecological
conditions of these communities and their ecosystems call for studies that facilitate
mainstreaming dry forest resources in development and conservation efforts (Lemenih and
Teketay 2004; Teketay 20042005; Worku et al. 2011).
Borana Zone, where this stud y was conducted, is located in southeastern Ethiopia.
In this zone, most of the landmass (69.1%) is characterized as arid and semi-arid (
Solomon et al. 2007). As described in Worku et al. (2011), Borana Zone houses several
valuable species in the genera Acacia, Commiphor,a and Boswellia, principal sources of
commercial gums and resins. These species are also often used for fodder and provide
herbal medicine (Dalle et al. 2005; Worku et al. 2011).
Despite the growing ecological and socioeconomic recognition of the dry woodland
resources in general, very little research has been done to understand the ecological and
population status of the dry woodland vegetation in Ethiopia (e.g., Eshete et al. 2005;
Lemenih et al. 2007; Abiyu et al. 2010; Eshete et al. 2011). In particular, detailed
information on the diversity and population status of gum and resin producing species is
scanty in the southern and southeastern parts of the country, although it is of crucial
importance for an integrated and sustainable management of these versatile resources.
The objectives of this study were to provide quantitative information on the species
diversity, abundance, regeneration status, and distribution of gum and resin bearing woody
species in Borana drylands, southern Ethiopia, and thereby to contribute to the ongoing
efforts to better integrate these resources in livelihood development and ecosystem
management in these dry woodlands.
Materials and methods
Study areas
Borana Zone (hereafter referred to as Borana) lies at the most south ern and southeastern
edges of the Oromia National Regional State, southern Ethiopia, between 36
0
42’ 38”’ to
39
0
45’ 15”’ E and 3
0
31’ 31”’ to 6
0
35’ 37”’ N (Figure 1). Most of the area falls under the
dry climatic regime with marginal or no agricultural potential. The mean annual rainfall
ranges between 400 and 600 mm (Dalle et al. 2005). The rainfall distribution is bimodal
with a short rainy season occurring between April and May and a major dry season
occurring between December and February (Dalle et al. 2005). The small monthly rainfall
is associated with a high evapo-transpiration rate, which makes the rainfall unabl e to
sustain good livestock and agricultural production (Sabine 2004). The human population
of Borana is estimated at about 400,000 (Dalle et al. 2005). The people of the study area
are called Borana, the eldest branch of the Oromo ethnic group in Ethiopia, and derive
their subsistence from livestock husbandry and small-scale traditional farming practices.
Most communities are dependent on the collection of various non-timbe r forest products
to generate income (Dalle et al. 2005; Worku et al. 2011).
The two districts (Arero and Yabello) where this study was conducted are covered with
woodlands dominated by an Acacia-Commiphora formation.
2 A. Worku et al.
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Data collection
In the Arero district, seven key informants were asked to list potential sites based on the
availability of gum and resin bearing species and the gum and resin collection history.
The informants were two elderly men representing local communities, two middlemen,
and three experts, one from the natural resources management department, one from a
local nongovernmental organization, and one from a gum and resin marketing company.
Seven potential sites were identified and four localities (Buno, Wachu Taka, Boji, and
Welensu) were randomly selected for vegetation assessment. A similar procedure was
applied in the Yabello district, where three localities (Harweyu , Adegeljet, and Ofuu) were
finally selected from the listed five localities.
To assess the diversity and population status of woody species, 75 (20 £ 20 m)
quadrats (43 at Arero and 32 at Yabello) were laid down at intervals of 500 m along
north-south transects. Transects were 500 m apart from each other. We used a similar
number of quadrats in each locality. In each quadrat, the identities of all woody species, as
well as the numbers of all individuals, including seedlings, were recorded. In addition, the
diameter at breast height (DBH) for individuals $ 2.5 cm diameter was measured.
Plant identification was mostly made in the field and, for those species which could not
be identified in the field, herbarium voucher specimens were collected and identification
was made at the National Herbarium at Addis Ababa University.
Figure 1. Map of Ethiopia showing location of the study areas.
Diversity of woody species 3
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Data analyses
The collected data were used to com pute species richness, diversity, evenness, similarity,
density, frequency, basal area, Importance Value Index (IVI), and population structure of
woody species in each study district. The species richness of woody plants was determined
from the total number of woody species recorded. The diversity of woody species was
determined using the Shannon-Wiener Diversity Index (H) and Evenness or Equitability
Index (E) (Magurran 1988). The similarity in woody species composition of the two
districts was computed using Jaccard’s Similarity Coefficient (S
j
) (Magurran 1988).
Density of woody species was determined by converting the total number of
individuals of each woody species encountered in all the quadrats to the equivalent number
per hectare. Relative density was calculated as the percentage of the density of each
species divided by the total stem number of all species ha
-1
.
Frequency, which refers to the degree of dispersion of individual species in an area,
was expressed as the ratio of the number of quadrats in which a species occurred to the
total number of quadrats, whereas relative frequency was computed as the ratio of the
frequency of the species to the sum total of the frequency of all species (Kent and Coker
1992).
The dominance of the woody species was determined from basal area (BA) for all
woody species with DBH . 2.5 cm. Relative dominance was calculated as the percentage
of the total basal area of a species out of the total basal areas of all species.
The IVI (Kent and Coker 1992) is used to give an overall indication of the importance
of a plant species in a plant community. It is the sum of the values of relative frequency,
relative density, and relative dominance of the speci es.
Biodiversity Professional Version 2 Software Program (Niel 1997) was used to run the
analyses of the vegetation data.
Results
Species richness
Forty-six woody species (41 at Arero and 23 at Yabello) representing 16 families and 25
genera were recorded (Table 1). Burseraceae and Fabaceae were the most diverse families,
each represented by 12 (26%) and 11 (24%) species, respectively. Commiphora and
Acacia, two of the genera with gum and resin producing species, were the first and second
most diverse genera, represented by 10 and 6 species, respectively. In total, 18 (39%)
species (17 at Arero and 14 at Yabello) were identified as sources of gums and resins.
However, according to respondents, three of these species, namely Acacia oerfota, Lannea
rivae, and Sterculia stenocarpa, were only occasionally visited and their gums collected
and mixed with other types of commercial gum.
Diversity, evenness, and similarity
The diversity of all woody species in Arero and Yabello were 3.22 and 2.77, respective ly,
while the corresponding values of evenness were 0.87 and 0.78, respectively. Similarly,
the diversity of gum and resin bearing woody species in Arero and Yabello were 2.6 and
2.23, respectively, while the corresponding values of evenness were 0.88 and 0.82.
The two sites shared 18 woody species in common, of which 13 were gum and resin
bearing species (Table 1). The similarity of all woody species (S
j
¼ 0.39) was low, while
that of gum and resin bearing species (S
j
¼ 0.72) was relatively very high.
4 A. Worku et al.
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Table 1. List of species encountered in the study quadrats at Arero and Yabello.
Arero Yabello
Scientific name Family RDE RFR RBA IVI RDE RFR RBA IVI
Grewia tembensis Fresen.
S
Tiliaceae 12.35 4.1 1.25 17.70
Grewia villosa Willd.
S
Tiliaceae 8.72 3 0.50 12.22 7.65 4.82 0.77 13.24
Boswellia neglecta S. Moore
*
T/S
Burseraceae 7.72 (15.0) 6.9 16.25 30.87 4.97 (4.3) 5.70 7.50 18.18
Acacia senegal (L.) Willd.
*
T/S
Fabaceae 7.58 (23.0) 6.5 2.50 16.58 9.18 (12.7) 7.89 4.75 21.82
Commiphora africana (A. Rich.)
Engl.
*
T/S
Burseraceae 7.10 (23.3) 6.9 5.00 19.00 6.50 (10.5) 6.15 5.97 18.63
Grewia bicolor Juss.
S
Tiliaceae 4.48 1.9 0.38 6.76 13.47 4.82 0.15 18.44
Blepharispermum sp.
S
Asteraceae 3.72 1.6 0.50 5.82
Harmsia sidoides K. Schum.
S
Sterculiaceae 3.72 1.9 0.25 5.87 2.60 0.88 0.46 3.94
Ipomoea donaldsonii Rendle
S
Convolvulaceae 3.72 1.8 0.50 6.02
Commiphora erythraea (Ehrenb.)
Engl.
*
T
Burseraceae 3.38 (4.0) 5.7 12.50 21.58 3.37 (1.1) 4.39 4.75 12.50
Commiphora confusa Vollesen
*
T
Burseraceae 2.86 (1.1) 5 7.50 15.36 10.71 (5.8) 10.96 21.44 43.11
Commiphora myrrha (Nees)
Engl.
*
T
Burseracea 2.81 (7.8) 3.7 2.50 9.01
Boswellia microphylla Chiov.
*
T/S
Burseraceae 2.67 (2.6) 3 3.75 9.42
Commiphora habessinica (Berg)
Engl.
*
T/S
Burseraceae 2.48 (1.5) 4.1 5.00 11.58 5.05 (4.9) 6.14 7.81 19.0
Acacia bussei Harms ex Sjo
¨
stedt
T
Fabaceae 2.34 4.2 7.50 14.04 2.60 4.82 6.13 13.55
Commiphora kua (R. Br. ex
Royle) Vollesen
*
T/S
Burseraceae 2.24 (1.1) 3.7 3.75 9.69 3.60 (3.8) 4.82 4.90 13.32
Acacia mellifera (Vahl) Benth.
*
T/S
Fabaceae 2.10 (6.5) 3.5 1.25 6.85 5.66 (12.9) 7.02 2.60 15.29
Dodonea angustifloia L. f.
T/S
Sapindaceae 2.00 0.7 0.25 2.95
Commiphora terebinthina
Vollesen
*
T/S
Burseraceae 1.72 (3.1) 3.2 2.50 7.42
Commiphora boranensis
Vollesen
*
T/S
Burseraceae 1.67 (2.9) 2.8 1.25 5.72 0.99 (0.9) 1.75 0.92 3.66
Diversity of woody species 5
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Table 1 continued
Arero Yabello
Scientific name Family RDE RFR RBA IVI RDE RFR RBA IVI
Commiphora schimperi (Berg)
Engl.
*
T/S
Burseraceae 1.43 (3.4) 2.7 1.25 5.38 1.84 (3.2) 3.07 1.99 6.90
Vernonia cinerascens Sch. Bip.
S
Asteraceae 1.29 0.5 0.38 2.16
Indigofora volkensii Taub.
S
Fabaceae 1.24 0.5 0.25 1.99
Lanea rivae (Chiov.) Sacl.
*
T
Anacardiaceae 1.19 (1.7) 3.5 5.00 9.69 1.22 (2.0) 3.51 2.91 7.64
Kirkia burgeri Stannard
S
Simaroubaceae 1.14 1.8 2.50 5.44
Premna schimperi Engl.
S
Verbenaceae 1.05 1.1 0.25 2.40
Acacia tortilis (Forssk.) Hayne
T
Fabaceae 1.05 1.8 2.50 5.35 3.14 5.7 6.89 15.73
Lanea triphylla (A. Rich.) Engl.
T
Anacardiaceae 0.95 0.5 0.50 1.95
Delonix ellata (L.) Gamble
T
Fabaceae 0.91 2.8 5.00 8.71
Plectranthus igniarius
(Schweinf.) Agnew
S
Lamiaceae 0.86 0.5 0.13 1.48
Commiphora corrugata Gillett &
Vollesen
*
T/S
Burseraceae 0.57 (0.7) 1.8 0.50 2.87
Sterculia stenocarpa
H. Winkler
*
T
Sterculiacea 0.48 (0.7) 2.3 2.50 5.28 0.54 (1.3) 1.32 1.07 2.93
Acacia oerfota (Forssk.)
Schweinf.
*
S
Fabaceae 0.48 (1.4) 0.7 0.38 1.55 2.30 (12.9) 3.91 0.31 5.67
Erythria melanacantha Taub. ex
Harms
T
Fabaceae 0.48 1.2 1.25 2.93
Maerua triphylla A. Rich.
T/S
Capparindaceae 0.43 0.5 0.38 1.30
Terminalia prunioides Laws.
T/S
Combretaceae 0.38 1.1 0.38 1.86
Delonix baccal (Chiov.) Bak. f.
T
Fabaceae 0.19 0.7 1.25 2.14
Sesamothamus rivae
T
Pedaliaceae 0.19 0.9 0.25 1.34
Terminalia brownii Fresen.
S
Combretaceae 0.14 0.2 0.25 0.59
Ormocarpum trichocarpum
(Taub.) Engl.
S
Fabaceae 0.14 0.4 0.13 0.67
Hibiscus crassinervius Hochst. ex
A. Rich.
S
Tiliaceae 0.05 0.4 0.13 0.57
Acacia seyal Del.
*
T
Fabaceae 10.71 (23.7) 8.34 17.0 36.05
6 A. Worku et al.
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Table 1 continued
Arero Yabello
Scientific name Family RDE RFR RBA IVI RDE RFR RBA IVI
Dicrostachys cinerea (L.) Wight
& Arn.
T/S
Fabaceae 1.30 0.88 0.15 2.33
Grewia tenax (Forssk.) Fiori
S
Tiliaceae 0.99 1.32 0.15 2.47
Balanites aegyptiaca (L.) Del.
T/S
Balanitaceae 0.54 1.75 0.92 3.20
Boscia mossambicensis Klotzsch
T
Capparidaceae 0.23 0.88 0.46 1.57
Total 100 100 100 300 100 100 100 300
Total density ha
-1
2,098 (805) 1,307 (331)
Total frequency 566 230
Total basal area 8 6.53
Note: RDE (%) ¼ relative density (figures in parentheses are seedlings); RFR (%) ¼ relative frequency; RBA (%) ¼ relative basal area; IVI ¼ Importance Value Index; S ¼ shrub;
S/T ¼ shrub/tree; T ¼ tree.
*
Gum and resin producing species.
Diversity of woody species 7
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Density, frequency, and dominance
The densities of all woody species, including seedlings, were 2,098 and 1,307 stems ha
-1
at
Arero and Yabello, respectively (Table 1). Of these, the gum and resin bearing species
accounted for 1,017 (about 49% of total) and 882 (about 68% of total) stems ha
-1
at Arero
and Yabello, respectively (Figure 2). A few species dominated the woody vegetation at the
two districts. For instance, five species, namely Boswellia neglecta, Acacia senegal,
Commiphora africana, Grewia tembensis , and G. villosa, contributed to 44% of the total
density at Arero, while Grewia bicolor, Commiphora confusa, Acacia seyal, A. senegal,
and G. villosa contributed to 53% of the total density at Yabello. Acacia senegal was the
only species with relatively high densities in the two study districts.
The three most abundant gum and resin producing species were B. neglecta, A. seneg al,
and C. africana at Arero, with 162, 159, and 149 individuals ha
-1
, respectively, and C.
confuse, A. seyal, and A. senegal, with 151, 140, and 120 individuals ha
-1
, respectively, at
Yabello. At Arero, the highest frequency (91%) was recorded for B. neglecta and C.
africana, each recorded in 39 out of the 43 quadrats, followed by A. senegal (86%),
recorded in 37 quadrats. Commiphora confusa and A. seyal were the most frequently
recorded gum and resin bearing species at Yabello, with frequencies of 78% and 59%,
respectively, followed by A. senegal and A. mellifera, each with 56 and 50% (Table 1). At
Arero, the minimum frequency was observed for A. oerfota (16%), while at Yabello it was
S. stenocarpa (9%). The total basal areas of woody species were 8.0 and 6.5 m
2
ha
-1
,in
Arero and Yabello, respectively, including 5.9 (73%) and 5.5 (84%) m
2
ha
-1
for gum and
resin bearing species (Table 1).
Importance Value Index
Gum and resin bearing species accounted for about 63 and 75% of the IVI at Arero and
Yabello, respectively. The species with the highest IVI were B. neglecta, C. erythraea,
C. Africana, and A. seneg al at Arero, and C. confusa, A. seyal, and A. senegal at Yabello
(Table 1).
Regeneration status and population structure
The total seedling density of gum and resin producing species were 344 and 152
individuals ha
-1
at Arero and Yabello, respectively. Species with the highest seedling
density were C. africana, A. seneg al, and B. neglecta at Arero, and Acacia seyal,
A. mellifera, A. senegal, and C. africana at Yabello (Table 1).
Figure 2. Proportion of the density (stem number) ha
1
of gum and resin bearing and associated
species at Arero and Yabello districts, respectively, Borana drylands, southern Ethiopia.
8 A. Worku et al.
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The population structure of the entire woody species showed higher stem densities in
the lower diameter classes and progressively declining stem densities with increasing
diameter classes at both districts (Figures 3a & 3b).
Based on their population structures, the gum and resin producing species can be
categorized into two diameter class distribution patterns. Group I contained species with a
progressively declining numbers of trees with increasing diameter (e.g., C. africana)
(Figure 3c). This group was comprised of A. mellifera, A. senegal, A. oerfota, C. africana,
C. myrrha , and C. schimperi at Arero and A. mellifera, A. senegal, A. oerfota, and
C. africana at Yabello. Group II was comprised of all other species from both
districts with a bell-shaped or irregular distribution (e.g., B. neglecta and C. confusa)
(Figures 3d & 3e).
Figure 3. Diameter size class distribution of the entire vegetation at Arero (a) and Yabello (b)
districts and three selected species (c e) in the Borana drylands and southern Ethiopia (diameter class
in cm: class 1 ¼ 04 cm, 2 ¼ 4–8, 3 ¼ 8 12, 4 ¼ 1216, 5 ¼ 1620, 6 ¼ 20 24, 7 ¼ 24 28 and
8 ¼ . 28).
Diversity of woody species 9
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Discussion and conclusions
The woodlands of Borana support diverse woody species, many of which produce gums
and resins of high socioeconomic importance, with good stocking density an d
considerable horizontal distribution (frequency). The Borana rangelands have also been
reported to house high floristic diversity with over 327 plant species (Dalle et al. 2005).
The richness in gum and resin bearing species in Borana is much higher than in other
woodlands in the country. For instance, only nine (Gebrehiwot 2003; Eshete et al. 2011),
two (Argaw et al. 1999), and seven (Lemenih et al. 2003) gum and resin bearing species
have been reported from northern, central, and southeastern Ethiopia, respectively,
compared with the 18 species reported here from Borana. In addition, the genus
Commiphora is represented by only one resin producing species, namely C. africana,in
northern Ethiopia (Gebrehiwot 2003; Eshete et al. 2011), compared with the ten species
reported here. Similarly, fewer gum and resin bearing species were reported from Eritrea
(Ogbazghi et al. 200 6) than those reported here.
The relatively high species richness, diversity, and abundance of gum and resin
bearing species in Borana indicate the existence of yet untapped resources that could be
used as viable options either for organized production and marketing by the local pastoral
and agropastoral communities to diversify their livelihoo ds and/or local, national, and/or
international private investments to develop the gum-resin subsector value chain.
Many authors use one form or another of the IVI to rank species in terms of their
ecological importance in the functioning of a plant community (e.g., Le
´
vesque et al. 2011;
Sunil et al. 2011). The fact that several of the gum and resin bearing species are among
those with the highest IVIs suggests that they are also among the most ecologically
important species. Most of the gum and resin bearing species are also multipurpose in
nature (Worku et al. 2011), for instance for improving soil condi tions or as sources of
fodder. This supports their integration into current initiatives to ensure food security,
combating desertification and mitigating climate change in the study areas (Lemenih and
Teketay 2004).
The population structure of woody species can help understand the regeneration status
of species and forest stands (Tesfaye et al. 2010; Zegeye et al. 2011). Reverse J-shaped
distributions such as those shared by Group I species in this study indicate a healthy and
stable regeneration (Harper 1977; Silvert own 1982). In contrast, bell-shaped distributions
(Group II species in this study) suggest hampered regeneration. This may be inherent to
the biology of the species or due to external factors, which require further investigation.
Despite indications of hampered regeneration, most of the species in Group II had a
considerable number of individuals in the middle diameter classes that could be managed
sustainably to improve their regeneration and produce gums and resins.
Generally, regeneration of the woody species was better at Arero compared with
Yabello, which might be attributed to more permanent settlements of people and farming
activities at Yabello, which are exerting continuous pressure on the woody vegetation
resources. As indicated by Dalle et al. (2005) and Worku et al. (2011), gum and resin
bearing species are among the main fodder species in Borana. Seedlings of some of the
Commiphora, Boswellia, and Sterculia species are browsed by small calves, goats, sheep,
and wild animals, which might have contributed to their poor regeneration compared to the
high seedling densities of Acacia species. Grazing was also mentioned as a major
detrimental factor for tree regeneration elsewhere in dry forests of the tropics (Miles et al.
2006; Staver et al. 2009). Commiphora corrugata, C. confuse, C. kua, and S. stenocarpa at
Arero and S. stenocarpa, C. erythraea, C. boranensis, and L. rivae at Yabello need special
10 A. Worku et al.
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attention since they were represented with only a few individuals of seedlings.
Commiphora corrugata showed the least IVI among the gum and resin bearing species.
The fact that it has the lowest density and frequency values suggests a patchy distribution,
and, thus, the need for measures to facilitate its regeneration.
Recurrent drought and severe degradation of rangelands in Borana drylands have made
subsistent livestock production and crop farming unpredictable and unable to support
livelihoods (Dalle et al. 2005; Worku et al. 2011). Food shortage is a common event, even in
normal seasons (Sabine 2004). Hence, income generated from the sale of gums and resins
has been identified as an important safety net during recurrent drought periods (Worku et al.
2011). In Borana, the need for environmentally friendly alternative strategies that help
diversify the livelihoods of pastoralists and agrop astoralists is more important than ever. In
this regard, our findings revealed that there is a huge potential for the sustainable
management and strategic integration of the gum and resin resources with other initiatives
targeting socioeconomic development and environmental conservation in Borana.
Further in-depth research is required to understand the biology and ecology of gum and
resin bearing species, mainly in view of their response to alarming climate and land-use
changes and to encourage their inclusion in plantation and domestication schemes. It would
also be beneficial to develop suitable tapping, processing, and handling technologies that
could add value to the products. Particular attention is required to address the hampered
regeneration of some of the species. With successful management and development,
promoting the integration of the gum and resin resources in Borana with the other ongoing
initiatives, through the active involvement of local communities, could be an appropriate
pathway to socioeconomic development and environmental conservation, as well as climate
change adaptation and mitigation.
Acknowledgements
This study was conducted with the financial support from Ethiopian Institute of Agricultural
Research (EIAR). The materials and facility support from Forestry Research Center is highly
acknowledged. We are very grateful to Temesgen Yohans, Dagnew Yebeyen, Dr. Wubalem
Tadesse, Dr. Deribe Gurmu, Dr. Abeje Eshete, Anteneh Belayneh, Alemayehu Negasa, Abel Gizaw,
Adane Girma, Worku Zewide, and Mengstie Kindu for their support.
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... In addition, recent studies (e.g. [5,11,12] reported existing opportunities to produce trade volume of gum karaya from Sterculia species in different parts of the country. Professional estimates show that Ethiopia has over 3.5 million ha of woodlands and bushlands with an estimated annual production potential of 270,000 tons of gums and resins [4]. ...
... Despite the diverse woody species harbored by the Combretum-Terminalia and Acacia-Commiphora vegetation resources and their huge socio-economic and ecological importance, these resources are under increasing anthropogenic and natural pressures [8,12,13]. This has resulted in severe degradation of habitats, soil and water resources as well as decline of biodiversity in the drylands of the country where these resources are common. ...
... Generally, species richness, abundance, dominance, frequency and IVI describe the floristic characteristics of an area. The numbers of woody plant species recorded at the study sites (18 at Sherkole and 23 at Kurmuk) are comparable to those reported from Aberegelle, northern Ethiopia (22 spp.; [5]) and Yabello, southern Ethiopia (23 spp.; [12]), where gum-and resin-bearing species are also common. However, the species richness values at the current study sites are far lower than those reported from Combretum-Terminalia forests in Metema, northern Ethiopia (78 spp.; [20]) and Acacia-Commiphora woodlands in Arero, southern Ethiopia (41 spp.; [12]). ...
Article
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Diversity, population structures, and regeneration status of gum- and resin-producing woody species, were assessed in 116 sample plots, each measuring 400 m2 and established along line transects. The data were collected in two selected districts, namely, Sherkole and Kurmuk in Benishangul-Gumuz National Regional State, one of the gums and resin belts in western Ethiopia. The gum- and resin-producing woody species had 1.04 and 0.7 diversity and 0.576 and 0.49 evenness values at Kurmuk and Sherkole districts, respectively. They accounted for 26% and 46% of the density, 51% and 58% of the basal area, and 32% and 53% of the Importance Value Index of all the woody species, respectively. The gum- and resin-bearing woody species exhibited three patterns of population structure. The first pattern suggests good reproduction abilities of the species coupled with a good recruitment of seedlings and their subsequent continuous growth to replace older individuals over time, indicating stable regeneration. About 61% of the gum- and resin-bearing woody species fall under this category. The other two patterns indicate the hampered regeneration status of the woody species. Heavy grazing, conversion to cropland by small-scale farming, gold mining, recurrent fire, and climate change were mentioned as major bottlenecks of natural regeneration and recruitment. Policy, extension, and research recommendations are discussed.
... Similar number of woody species recorded in similar dry forest in Metema area [16]. Similarly, approximated numbers of woody species were recorded from Borena dry land vegetation [17]. ...
... According to Work [17], classification the upper story is taken as tree height >2/3 of top height, middle story as tree height between 1/3 -2/3 of the top height and the lower story as tree height <1/3 of the top height. The top height attained in Higelely dry forest was 18 m; therefore, the upper story of this forest was 13 -18 m, middle story 7 -12 m and lower story <7 m. ...
... Some of the species such as Acacia bussei and Acacia mellifera encountered in the upper story are also encountered in the middle and lower story. Such kinds of species are considered to be "species with a regular vertical distribution" [17]. ...
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Dry forests are potentially contributed for the local community livelihood, microclimate stability and biodiversity conservation. However, appropriate emphasis has not given for its sustainability management. Our study aims to study the woody species diversity, vegetation structure, and recruitment and regeneration status in Higelely dry forest of Somali National Regional State of Ethiopia for the purpose of conservation priority. Systematic sampling following the transect lines and sample plots employed to collect all necessary data. Data were analyzed using access software which was designed for the purpose of forest genetic resource conservation database and data analysis tool. Forty two woody species belongs to 21 genera and 15 families were recorded. The richest families were Fabaceae and Burseraceae (represented by 11 and 7 species each). 1112.97 individuals of woody species per ha was recorded in Higelely forest. Acacia oerfota and Acacia mellifera were the top specie with higher stem numbers per ha. More than 67% of the individuals in the forest had DBH/DSH ≤ 7.5 cm and 90% of the individuals had a height ≤ 5 m. The most ecologically important species in Higelely forest were Acacia oerfota, Acacia mellifera, and Acacia bussie. Whereas, Ipomoea donaldsonii, Commiphora africana, and Acacia drepanolobium were the most threatened species in all criteria's of IVI, population structure and regeneration status and are the first prioritized for conservation measures. The total density of 1047.3 seedling and 3033.77 sapling individuals per ha was recorded in Higelely forest. In general, the vegetation structure, population recruitment and regeneration status of some species indicates, Higelely forest is under poor conservation status. Therefore, for the conservation of woody species in Higelely dry forest, appropriate conservation measures such as in-situ (to allow natural regeneration) and cold room seed storage methods are recommended.
... It was noted that in areas accessible to the public, the density tends to be low (Phama et al., 2014). Anthropogenic activities in communal areas can drive a vegetation into patchiness or narrow distribution of plant species (Worku et al., 2012;Nasrullah et al., 2015). A study by Sadiki et al., (2018) on Pterocarpus angolensis population in a protected area revealed a density of 9.62 individuals, per hectare. ...
... Similar results were recorded by Cousins et al., (2014); Kflay & Kitessa, (2014) who also observed high numbers of individuals in the middle classes compared to the number of individuals in both low and high stem-size classes. A bell-shape curve shows a hampered regeneration because of external factors (Worku et al., 2012). The decrease of adult trees and lack of regeneration showed a decline in the population of plant species (Bayen et al., 2015). ...
... Drylands of Ethiopia host forests that are comprised of the largest proportion of forest resources which accounts for about 48% of the total land mass (WBISPP, 2004). These forest lands are endowed with the major gum and resin producing genera of Acacia, Boswellia and Commiphora vegetations which have contributing cultural, economic and ecological importance (Worku et al., 2012). Gums and resins are the most widely used and traded NTFPs other than items consumed directly as food, fodder and medicine (Lemenih and Teketay 2003a). ...
... C. africana, B. coriacea, A. schimperiana, O. americanum, Lannea schimperi, and Commiphora boranensis were among the species with relatively high IVI at study area, which shows that these species were among the best adapted, dominant and with more or less good population status in the area. Similar results were also reported from Arero and Yabello districts in Borana Zone where woody species contributed relatively high IVI, respectively (Worku et al., 2012). Also Issango (2004) showed that woody species with high resistance to anthropogenic disturbance and those with efficient regeneration capacity have relatively high chance of remaining the dominant and important species at an area. ...
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Boswellia neglecta which is among the resin bearing species is dominantly found in the dry Acacia–Commiphora woodlands of the South and South Eastern parts of the country. It is a small tree that produces commercially important oleo-resin known as frankincense. This frankincense has been used for varied purposes, and it is a source of income for rural households in southern and south-eastern Ethiopia. Among this incense of B. neglecta is widely used in Ethiopia, and traded as ‘Borena type’ olibanum. The Borana-type frankincense is produced from B. neglecta growing in the Southern and South-Eastern part of the country ( it is locally named as “tikuretan” (meaning: black incense). Internationally the resin/frankincense is an important commodity as it is a source of essential oils, cosmetic and pharmaceutical industries. Above all, B. neglecta is one of economically important tree species with higher density and higher IVI in study area but has a poor regeneration status. Therefore, there should be an improved management activity on woodland and appropriate tapping technology for a sustainable resin production. Also, more research is recommended to see the market value and to identify biological activities of essential oil in the agro-chemical industry.
... The evenness (E) values of all forage species were in between 0.78 and 0.86 across the sampled plots (Table-2). The numbers of forage plant species recorded at the study sites are comparable to those reported from Gambella, southwestern Ethiopia [16] and Yabello, southern Ethiopia [17]. 21 ), RDE ¼ relative density (%), FR ¼ absolute frequency (%), RFR ¼ relative frequency (%), DO ¼ absolute dominance (m 2 ), RDO ¼ relative dominance (%) and IVI ¼ Importance Value Index. ...
... The forage plant species reported from Guba are among the woody species with relatively high ecological importance, which is clearly reflected in their contribution to the overall IVI of the study sites. Similar results were also reported from Metema districts in Amhara Regional State where woody species contributed 65% and 75% of the total IVI, respectively [17]. ...
... In the low grazed area, IVI values ranged from 5.27 (Vachellia nilotica) and 53.39 (Vachellia tortilis) ( Table 1). The IVI value is directly related to abundance, basal area, density and frequency distribution, and is an important parameter indicating the ecological significance of a species in a given ecosystem (Worku et al., 2012;Tsegay et al., 2017). The species with high IVI values are considered more important than those with low IVI values for conservation program and managements by the community and other stakeholders before the disappearance (Tsegay et al., 2017). ...
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... m 2 ha -1 reported by Jha and Singh (1990) for several dry tropical communities in India. Similarly, the overall population structure of woodlands can help understand the status of the forest stand (Tesfaye et al., 2010;Worku et al., 2012). Reverse J-shaped distributions such as those shared by Group I species in the Gemed site indicate more or less a healthy or stable regeneration. ...
Thesis
Full-text available
A major problem being faced by human society is the rising of global temperature mainly due to human activity that emit carbon dioxide to the atmosphere. The problem of increasing atmospheric carbon dioxide can be addressed in a number of ways. One of such actions is forestry development and forest management undertakings. Sustainable forest management and development is believed to be an asset for increasing societal adaptive capacity to climate anomalies. This paper examined the potential of the dry western woodlands of Ethiopia for carbon sequestration in response to woodland cover changes. The study was based on the assumption that increasing societal adaptive capacity is possible through asset building from financial earnings obtained from carbon trading and non-timber forest products, especially gum and resin from Boswellia papyrifera woodland. GIS and RS were used to determine the LULCC. To estimate the amount of carbon stocked in dry land forests; vegetation inventory including dead wood, litter and herbaceous biomass collection were conducted in the 36 sample plots across the three districts of the study area namely: Kafta-Humera 17 plot, Metema 9 plot and Sherkole 10 plot. The sample plots were taken in transects line method in the two categories of woodlands, untapped and tapped Boswellia papyrifera. A total of 24 species were recorded. The soil samples were taken from 0-30 cm soil depth to determine the potential of soil carbon sequestration. To analyze the total woodland carbon stock, allometry equations were used to determine the aboveground, belowground and dead woods biomasses; litter and herbaceous biomasses were determined using direct harvesting method; and the SOC was estimated using standard methods. The result showed, the estimated mean carbon stocks of the aboveground, belowground and the dead wood biomasses for the UW in the Lemlem Terara site were significantly higher (P < 0.05) than that of the Adi Goshu site. In the Gemed site, the mean HBC stock was 1.2 Mg ha-1, which is significantly highest (P=0.0207) than the other two study sites (Lemlem Terara, 0.42 Mg/ha and Adi Goshu, 0.45 Mg/ha) for the TW. In UW, the mean soil carbon stock of the Lemlem Terara site (58.19 Mg/ha) was significantly (P=0.0019) higher than that of Adi Goshu (33.61 Mg/ha). However, no statistical variation (P=0.8884) was observed between the mean soil carbon stocks across sites in the tapped stratum. In the case of the total carbon stocks in UW stratum, for the Adi-Goshu site the carbon stock was estimated to be about 55.26 Mg/ha while 96.74 Mg/ha for Lemlem Terara. In the TW stratum, however, the total carbon of Adi-Goshu, Lemlem-Terara and Gemed sites were 65.93, 68.77 and 71.01 Mg/ha respectively. The results of LULCC analysis showed that in all study sites the classes of agricultural and bare land have been increased at an average rate of 2,322.94 and 726.58 ha/year, respectively; while the woodland coverage in the three district was decreasing at an average rate of 2,833.77 ha/year during the last 25 years (1985-2010). The woodland coverage was converted mainly to agriculture at an average rate of 2,057.9 ha/year. Despite the rapid decline in the woodland coverage, the existing wood land has a huge potential for carbon sequestration, which calls for the promotion of sustainable woodland management in this climate sensitive areas. From the view of points of woodland management in a sustainable manner, the study suggested that the NGPME and the regional government should made fundamental thinking in the policy of woodland management in such a way of promoting carbon trading for additional financial incentive to the local community who are depending on the woodland resource. The data obtained from the current study can be used as a baseline data set of carbon stock to make inferences about the carbon stocking in the areas where the study was conducted.
... Population structure of species can help in understanding the regeneration patterns of species and forest stands (Worku et al., 2012). Population structures, characterized by the presence of a sufficient population of seedlings, saplings, and young trees, indicate a successful regeneration of forest species (Saxena and Singh, 1984). ...
Article
Full-text available
The species composition in the aboveground vegetation and soil seed bank (SSB) were described for the dry Afromontane forest patches of Northwestern Ethiopia. Plots (30 × 30 m) were established to collect the vegetation and environmental data. Soil samples were collected for the soil bank study from the small plots measuring 10 cm × 10 cm from four soil layers. Shannon Weiner index and evenness were used to assess the species diversity and richness of the forest. Density, DBH, basal area, frequency, and importance value indices (IVI) of woody species were computed to characterize the vegetation structure of the forest. Results indicate the presence of 176 plant species belonging to 80 families. The Shannon diversity index and evenness values of the study area were 2.79 and 0.95, respectively were medium, compared to other dry Afromontane forests of Ethiopia. The total basal area and density of woody species were 51.42 m² ha⁻¹ and 2679.33 individual ha⁻¹, respectively. The most dominant species as and indicated by their important value index (lVI) was Prunus africana (17.97). A total of 2133 seedlings belonging to 44 species and 27 families were identified from the soil seed bank, with a viable seed density of 4636.95seeds/m2. The species composition of the seed bank was dominated by 29 herb species (65.9%) compared to 2 tree species, which accounted for only 4.54% of the total number of species. The highest number of species density was recorded in the litter and the upper 3 cm layer of the soil and gradually decreased with increasing depth. The Similarity between soil seed bank species composition and aboveground vegetation was low and conclude that the regeneration potential of the forest from seed bank is limited. Redundancy analysis (RDA) showed that emerged seedlings from the soil seed bank were significantly influenced by elevation and soil cation exchange capacity. The natural regeneration process of soil seed bank should be assisted through transplanting indigenous tree species in to the forests to accelerate the restoration of the vegetation and conservation and sustainable utilization of the reaming of forest patches is a necessity.
... In contrast, the relatively higher density of individuals in higher diameter size-classes might be explained by the fact that mature trees are purposely conserved in the fields for food, fuel, or timber. The Importance Value Index (IVI) calculated from the relative density, relative frequency and relative dominance of species indicates the ecological importance of species in a given ecosystem (Worku et al., 2012;Premavani et al., 2014). It is a conservation tool that allows knowing the species requiring urgent conservation needs (low IVI value) and those requiring enhanced monitoring efforts on their population (high IVI value) (Gurmessa et al., 2012). ...
Article
Parkia biglobosa (Jacq.) G. Don, Pterocarpus erinaceus Poir, Milicia excelsa (Welw.) C. C. Berg, Prosopis africana (Guill., Perrot. and Rich.) Taub., Afzelia africana Sm. and Khaya senegalensis (Desv.) A. Juss. are the most highly valued indigenous tree species in the agroforestry systems of the Ouémé catchment area. However, information on the population structure of these species is lacking, thus limiting the development of their sustainable conservation, utilization and restoration strategies. This study addressed this gap. It assessed the population structures and regeneration status of the six species from Don, Tan-Houègbo, Atchabita, Bétékoukou, Glazoué, Tchaorou, Zagnanado, Tévèdji, Sinaou and Bétérou along the catchment. Data were collected from 78 permanent rectangular plots (50 × 30 m) randomly installed within 10 provenances. Dendrometric data including diameter at breast height (dbh) of adult trees (dbh ≥ 10 cm), collar diameter, total height of seedlings and saplings, number of individuals per species according to adult, sapling and seedling were recorded. The population structure was described using ecological and dendrometric parameters (relative frequency, importance value index (IVI), mean densities, basal area, mean height), and diameter size-class distributions. Seedling:sapling and sapling:adult ratios were also computed and analyzed for determining regeneration patterns. Based on IVI, Parkia biglobosa (95.85%) and Khaya senegalensis (65.92%) were the most represented species in the catchment area. The analysis of variances showed that dendrometric parameters of the six species varied significantly between provenances. Seedling:sapling and sapling:adult ratios were
... The ecological significance of species in a given ecosystem can be described by their important value index (Worku et al., 2012). High IVI values of a species implies more ecologically important than low IVI values of the species (Zegeye et al., 2011). ...
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