PRIME Project
ASSESSMENT OF CARBON STOCK OF RANGELAND
SYSTEMS IN SELECTED PASTORAL AREAS OF SOMALI,
AFAR AND OROMIA REGIONS
Kibebew Kibret (PhD) and Tesema Toru
i
Haramaya University
2014
PRIME PROJECT
HU
Assessment of Carbon Stock of Rangeland
Systems in Selected Pastoral Areas of Somali,
Afar and Oromia Regions
A Draft Report
By
Kibebew Kibret (PhD)
Tesema Toru
November 2014
Haramaya University
ACKNOWLEDGMENTS
The authors would like to express their sincere gratitude to all those
who contributed, directly or indirectly, to the successful start and
completion of this project. The technical, financial support and
facilitation of all the field work by the PRIME project is highly
acknowledged. The support provided, in every aspect, by the
Haramaya University PRIME project management during the field
work deserves special gratitude. The authors also express their
indebtedness to the cluster level PRIME staff and staff members of
the PRIME project partners who were actively involved in selection of
the study sites, assignment of local staff as a guide and facilitation of
the field work at the respective clusters. Without their true dedication
and commitment, and also involvement in the actual field work, the
difficult field work would not have been completed successfully.
The cooperation of the pastoral communities during the field work is
also highly appreciated. Worth mentioning among these is the
amazing hospitality the authors received during the field work at
Harshin where the team’s vehicle was stuck in a mud and had to
spend the night there. Long live to the Harshin community. The
authors are also grateful to Mr. Kassaw Asfaw and Mr. Yitages Tamiru
for their unreserved contribution in the collection of vegetation and
soil samples, and laboratory analysis of the samples.
Last but not least by any means, the authors greatly acknowledge
the support provided by pertinent local government offices by
assigning staff members to facilitate the field work when needed.
EXECUTIVE SUMMARY
Pastoralism in Ethiopia is a direct source of livelihood to more than 7
million people who live in the vast lowlands and drought-prone areas.
These areas make up about 40% of the total land area of the
country. Despite living in the most fragile ecosystems, pastoralists
and pastoralism make significant contribution to the national
economy through livestock products. However, significant areas of
these lands are affected by degradation. Climate change is predicted
to have even a larger impact on these fragile ecosystems. On the
other hand, the great potential of these lands for carbon
sequestration has been highlighted. Their management can help in
mitigating climate change. Different rangeland management
practices have been tried over the years. Nevertheless, the impacts
of these management practices on the rehabilitation of rangelands
and their carbon stock have not been assessed to provide
quantitative information to inform policy in these areas. PRIME
project
has
started
implementing
participatory
rangeland
management scheme in pastoral areas of Somali and Afar regional
states, and Borena and Guji zones of Oromia region. It is imperative
to have baseline carbon stock information to evaluate the difference
this management scheme might bring about after five years. This
study was conducted to achieve this grand objective.
This study was conducted at three PRIME project target clusters,
namely east cluster, Afar cluster, and south cluster with the objective
of assessing carbon stock of grazing systems that are put under
participatory rangeland management scheme. The East cluster
encompasses the Somali Regional state, while the South cluster
includes Borena and Guji zones of Oromia region. Harshin, Daketo,
Mulu, and Afdem grazing systems were included from the East
cluster; Mollale, Halydege, and Dudub grazing systems were selected
from the Afar cluster; Malbe and Dire grazing systems from Borena
zone, and Dida Dheda and Golba Genale grazing systems from Guji
zone were selected from the South cluster. Both vegetation and soil
samples were collected from field and analyzed for their carbon
content. The results of the study reveal that the studied grazing
lands in pastoral areas have immense potential to serve as carbon
sinks both in soils and living vegetation. The results obtained in this
study can help decision makers to guide their policy towards
rangelands in pastoralist areas.
LIST OF ACRONYMS
ABTB
AD
AD
AGB
AGWV
BD
BGB
CSA
CV
DBH
DDH
DE
DH
DK
DM
EBL
EGL
FAO
GB
GB
GDP
GG
HD
HG
HS
HV
IFPRI
ILRI
IPCC
IR
IRIN
JJ
KL
LEAD
MC
ME
MS
MSP
MSUP
NGO
Aboveground Tree Biomass
Andido at Halydege
Arbala Dida at Malbe
Aboveground biomass
Aboveground Woody Vegetation
Bulk Density
Belowground biomass
Central Statistical Authority
Coefficient of Variation
Diameter at Breast Height
Dida Dheda in Guji
Dire Ella in Afdem
Dida Haya at Malbe
Dubuluk at Dire
Dida Medhecho at Dire
Elbahey Bush Land
Elbahey Grassland
Food and Agriculture Organization of the United Nations
Gointa Birka
Guduba Burure in Golba Genale
Gross Domestic Product
Golba Genale in Guji
Hudud at Dudub
Halydege village
Hussein Semane
Herbaceous Vegetation
International Food Policy Research Institute
International Livestock Research Institute
Intergovernmental Panel on Climate Change
Irrebeto at Dudub
Integrated Regional Information Networks
Jejeba in Mulu
Kulmeye in Mulu
Leadership for Environment and Development
Mucho in Golba Gonale
Mecha in Mulu
Motor Sefer at Dudub
Meesa Protected at Dida Dheda
Meesa Unprotected at Dida Dheda
Non-governmental Organization
Acronyms (Continued)
OAU
PRIME
RC
SS
StD
STP
STUP
UNEP
WOCAT
WRI
Organization of African Unity
Pastoralist Areas Resilience Improvement through
Market Expansion
Rare Chebicha at Dire
Siselu in Afdem
Standard Deviation
Siminto Protected at Dida Dheda
Siminto Unprotected at Dida Dheda
United Nations Environment Program
World Overview of Conservation Approaches and
Technologies
World Resources Institute
TABLE OF CONTENTS
ACKNOWLEDGMENTS
iii
EXECUTIVE SUMMARY
iv
LIST OF ACRONYMS
v
LIST OF TABLES
ix
LIST OF FIGURES
x
LIST OF PLATES
xii
ABSTRACT
xiv
1. INTRODUCTION
1
1.1. Background
1
1.2. Overall Objectives and Expected Result Linkage
4
2. METHODOLOGY
4
2.1. General Description of the Study Areas
4
2.2. Sampling Site Selection
5
2.3. Field layout for above ground vegetation sampling
7
2.4. Estimation of vegetation carbon stock
8
2.5. Soil Sampling and Preparation for Soil Carbon Stock Assessment
9
2.6. Estimation of Soil Carbon Stock
10
2.7. Estimation of Terrestrial Carbon Stock and Carbon Dioxide Equivalent
11
3. KEY FINDINGS
12
3.1. East Cluster
12
3.1.1. Terrestrial Carbon Stock of Harshin Grazing System
12
3.1.1.1. Overview of the grazing system
12
3.1.1.2. Results and discussion
14
3.1.2. Terrestrial Carbon Stock at Daketo Grazing System
16
3.1.2.1. Overview of the grazing system
16
3.1.2.2. Results and discussion
17
3.1.3. Terrestrial carbon stock of the Mulu grazing system
19
3.1.3.1. Overview of the grazing system
19
3.1.3.2. Results and discussion
21
3.1.4. Terrestrial Carbon Stock of the Afdem Grazing System
22
3.1.4.1. Overview of the system
22
3.1.4.2. Results and discussion
24
3.2. The Afar Cluster
27
3.2.1. Terrestrial carbon stock of Gewane Grazing System
27
3.2.1.1. Overview of the grazing system
27
3.2.1.2. Results and discussion
28
3.2.2. Terrestrial carbon stock of Halaydege grazing system
29
3.2.2.1. Overview of the system
29
3.2.2.2. Results and discussion
31
3.2.3. Terrestrial carbon stock of the Dudub grazing system
32
3.2.3.1. Overview of the system
32
3.2.3.2. Results and discussion
34
3.3. South Cluster
36
3.3.1. Terrestrial carbon stock of Malbe Grazing System
36
3.3.1.1. Overview of the system
36
3.3.1.2. Results and discussion
38
3.3.2. Terrestrial carbon stock of Dire grazing system
40
3.3.2.1. Overview of the system
40
3.3.2.2. Results and discussion
42
3.3.3. Terrestrial carbon stock of the Dida Dheda grazing system
44
3.3.3.1. Overview of the system
44
3.3.3.2. Results and discussion
46
3.3.4. Terrestrial carbon stock of the Golba Genale grazing system
48
3.3.4.1. Overview of the system
48
3.3.4.2. Results and discussion
49
4. CONCLUSIONS
52
5. RECOMMENDATIONS
54
REFERENCES
55
LIST OF TABLES
Table 1. Study sites selected for carbon stock assessment and
their basis characteristics
Table 2. Terrestrial carbon stock and its carbon dioxide
equivalent (t ha-1) at the Hussein Semane sub-grazing
system in Harshin, Somali region
Table 3. Terrestrial carbon stock of the Elbahey grazing subsystem in Daketo grazing system of Somali region
Table 4. Terrestrial carbon stock at three grazing sub-systems in
Mulu grazing system, Somali region
Table 5. The terrestrial carbon stock and its carbon dioxide
equivalent at two grazing sub-systems in Afdem grazing
system, Somali region
Table 6. Soil carbon stock and its carbon dioxide equivalent at
Mollale grazing sub-system Gewane, Afar region
Table 7. Terrestrial carbon stock and its carbon dioxide
equivalent at the Halydege grazing system in Afar
region
Table 8. Terrestrial carbon stock and its carbon dioxide
equivalent at the Dudub grazing system in Afar region
Table 9. Terrestrial carbon stock and its equivalent carbon
dioxide at Malbe grazing system, Borena zone of
Oromia region
Table 10. Terrestrial carbon stock and its carbon dioxide variation
with soil depth at three sites in Dire grazing system,
Borena Zone
Table 11. Terrestrial carbon stock and its carbon dioxide
equivalent at some grazing site in Dida Dheda grazing
system, Guji zone of Oromia region
Table 12. Terrestrial carbon stock and its carbon dioxide
equivalent at Golba Genale grazing system in Guji zone
of Oromia region
6
15
19
21
25
29
31
34
39
42
47
50
LIST OF FIGURES
Figure 1. Location map of sampling sites at the different grazing
systems in the three clusters. Error! Bookmark not defined.
Figure 2. Carbon stock and CO2e (t ha-1) variation with soil depth
at the Hussein Semane grazing sites in Harshin grazing
system, Somali region (HS = Hussein Semane).
16
-1
Figure 3. Carbon stock and CO2e (t ha ) variation with soil depth
for selected grazing sites in Dakato grazing system (EBL
= Elbahey bush land; EGL = Elbahey graa land).
19
Figure 4. Carbon stock and CO2e (t ha-1) variation with soil depth
at selected grazing sites in Mulu grazing system (ME =
Mecha; KL = Kulmeye; JJ = Jejeba).
22
Figure 5. Variation of soil carbon stock and the corresponding CO 2e
with soil depth at selected grazing sub-systems in
Afdem, Somali region (DE = Dire Ella; SS = Siselu).
25
Figure 6. Mean terrestrial carbon stock and its carbon dioxide
equivalent (t ha-1) at four pastoral area grazing systems
in Somali region.
26
Figure 7. Soil carbon stock and its carbon dioxide equivalent
distribution with soil depth at Mollale sub-grazing
systems in Gewane, Afar region.
29
Figure 8. Soil carbon stock and its carbon dioxide equivalent
variation with soil depth at selected sites in Halydege
grazing system, Afar region (AD = Andido; HG =
Halydege; GB = Gointa Birka).
32
Figure 9. Soil carbon stock variation with soil depth at selected
sites in Dudub grazing system in Afar region (IR =
Irrebeto; HD = Hudud; MS = Motor Sefer).
35
-1
Figure 10. Mean terrestrial carbon stock and its CO2e (t ha ) at
selected grazing systems in Afar region.
35
Figure 11. Soil carbon stock and equivalent carbon dioxide
variation with soil depth at the Malbe grazing system in
Borena zone of Oromia region (AD = Arbala Dida; DH =
Dida Haya; P = protected; up = unprotected).
39
Figure 12. Soil carbon stock and its carbon dioxide equivalent
distribution with dept at selected site in Dire grazing
system of Borena Zone, Oromia region (DK = Dubuluk;
RC = Rare Chebicha; DM = Dida Medhecho).
43
LIST OF FIGURES (Continued)
Figure 13. Mean terrestrial carbon stock and its carbon dioxide
equivalent for Malbe and Dire grazing systems in Borena
Zone of Oromia region.
Figure 14. Soil carbon stock and the corresponding carbon dioxide
equivalent variation with soil depth at selected sites in
Dida Dheda grazing system, Guji zone of Oromia region
(MSP = Meesa protected; MSUP = Meesa unprotected;
STP = Siminto protected; STUP = Siminto unprotected).
Figure 15. Soil carbon stock and its carbon dioxide equivalent
distribution with soil depth at Golba Genale grazing
system, Guji Zone of Oromia region (GB = Guduba
Burure; MC = Mucho).
Figure 16. Mean terrestrial carbon stock and its carbon dioxide
equivalent at two grazing systems in Guji Zone, Oromia
region (DDH = Dida Dheda; GG = Golba Genale).
44
47
50
51
LIST OF PLATES
Plate 1. Partial view of the Hussein Semane sub-grazing system
sampling sites, nature of vegetation cover, and stocking
density in Harshin grazing system.
Plate 2. Partial view of the Elbahey sub-grazing system in Daketo; A
and B show the upper smapling plot dominantly occupied by
cactus and Lanthana camara, and B and C show the second
sampling site in Daketo valley with annual herbaceous
vegetation.
Plate 3. Nature of vegetation, vegetation data (measuring tree
diameter and weighing fresh biomass of herbaceous
vegetation), vegetation and soil sample collection activities
at the three grazing sub-systems in Mulu grazing system.
Plate 4. Partial view of the highly degraded vegetation and soil in
Afdem grazing system at Dire Ella and Siselu, and the
livestock that are desperate to get some feed from these
highly degraded grazing lands.
Plate 5. The partial view of the Mollale sub-grazing system in
Gewane. Prosopis juliflora is being cleared from this field
(bottom) and the soil was devoid of any other vegetation.
Plate 6. The extensive grazing lands located at the low lying areas in
Halydege were devoid of grass vegetation at the time of
sampling. However, Prosopis juliflora is still proliferating at
some of the sites.
Plate 7. Some features of the grazing lands in Dudub grazing system.
The soil is bare except the scattered bushy vegetation cover
and is highly prone to wind erosion.
Plate 8. The nature of the extensive plain grass land at Arbala Dida
(upper), soil and vegetation sampling activities (bottom left),
and protected and adjacent unprotected grazing land
(bottom last two) at Dida Haya at Elwaye sub-grazing system
in Malbe. Note that the Arbala Dida grazing land is also home
to some wild animals such as ostrich.
Plate 9. Partial view of the three sub-grazing systems and their
status of vegetation cover at the Dire grazing system. Near
the hills, the Dubluk sub-system is home to some wild
animals like zebra.
13
17
20
23
28
30
33
37
41
LIST OF PLATES (Continued)
Plate 10. Partial view of the sampling sites at Meesa (upper) and
Siminto (lower) sub-systems at Dida Dheda grazing system.
The upper and bottom left photos indicate the protected
kallos at both sub-systems, while the adjacent ones indicate
the unprotected grazing lands.
45
Plate 11. Partial view of the sampled forest at Guduba Burure
(upper), active participation of local partners in the study
(bottom left), and nature of some trees at Mucho sampling
site in Golba Genale grazing system.
49
ABSTRACT
A study on carbon stock assessment in pastoral PRIME target areas was
conducted in Somali, Afar, and Oromia Regions. The baseline carbon
stock was assessed based on measurements made on vegetation and
soil samples collected from selected sites in grazing systems.
The baseline mean terrestrial carbon stock and its carbon dioxide
equivalent in Harshin grazing system was 73.924±26.426 and
271.301±96.984 t ha-1, respectively. The corresponding values for the
Daketo system were 90.203±42.837 and 331.045±157.210 t ha-1,
respectively. At Mulu grazing system, the baseline mean carbon stock
and the corresponding baseline mean CO2e were 160.536±31.477 and
589.166±115.521 t ha-1. At Afdem the stock was relatively low
(58.622±9.296 and 215.143±34.118 t ha-1 of carbon and equivalent
carbon dioxide, respectively).
At Mollale in Gewane, the carbon source was only the soil and it was
33.43 tha-1. The baseline mean value of the carbon stock and its carbon
dioxide equivalent for the Halydege grazing system was 45.628±3.463
and 167.456±12.708 t ha-1, respectively. The corresponding values for
Dubluk system were 29.519±17.771 t ha-1 carbon with equivalent
carbon dioxide of 108.335±65.220 t ha-1.
The mean terrestrial carbon stock and the corresponding carbon dioxide
equivalent for the Malbe system were 60.962±14.110 and
223.729±51.785 t ha-1, respectively, while the corresponding values at
Dire, Dida Dheda, and Golba Genale were, respectively, 81.697±20.248
and 303.498±74.312, 67.687±17.585 and 248.411±64.537, and
138.026±11.350 and 506.556±41.656 t ha-1.
Comparison of the carbon stock in protected and unprotected grazing
lands at Malbe and Dida Dheda grazing systems indicates that the
contribution from herbaceous vegetation is higher in the protected than
it is in the unprotected grazing lands. However, due to intensive grazing
after protection and relatively short duration of the protected
vegetation, this difference was not clearly reflected in the soil carbon
stock. This clearly indicates that implementing participatory rangeland
management practice in combination with controlled grazing and
stocking could improve the contribution of both vegetation and soil to
the total carbon stock of the grazing systems. This will in turn improve
the productivity of the grazing systems through the favorable effects of
organic carbon on soil properties, improve productivity of livestock
through improving feed supply and eventually increase the resilience of
the pastoral community to climate change impacts. Furthermore, the
results obtained in this study suggest that management of grazing
systems in pastoral areas could be among the options to mitigate
climate change impacts as these areas are vast in their extent and have
high potential to store carbon in live vegetation and soils.
1. INTRODUCTION
1.1. Background
Livestock production, the main land use in pastoral areas and a source of
livelihood for over 1 billion people (World Bank, 2007), can be found on
two thirds of global drylands (Clay, 2004; Nori et al., 2005). About 60%
of the 690,000 poor people living in sub-Saharan Africa rely on livestock
for some part of their livelihood (Thornton et al., 2002). On the other
hand, the report of IFPRI and ILRI (2000) indicate that 25 million
pastoralists and 240 million agro-pastoralists living in sub-Saharan Africa
depend on livestock as their primary source of income. The dedication of
about 40% of Africa’s land to pastoralism highlights the importance of
livestock to the livelihood of Africans (IRIN, 2007).
Livestock products, being the main outputs of grazing lands, have become
among the fastest growing agricultural subsector globally. The World
Bank (2007) report indicates that the contribution of the livestock sector
accounts for 50-80% of some developing countries’ GDP, while the share
in sub-Saharan Africa is estimated at 12.5%. This indicates the social and
economic importance of livestock to rural livelihoods, and thus the
sustainable management of the natural resources base that supports
them should stand high on the agenda.
Estimates made by various studies (WRI, 2002; UNEP, 2006) indicate that
drylands, which are predominantly used for livestock production, occupy a
significant 41 per cent of the earth’s land area and are home to more
than 2 billion people. Nevertheless, these expansive lands are particularly
sensitive to land degradation, with 10–20 percent of them already
degraded (Millennium Ecosystem Assessment, 2005). In connection with
this, the report released by WOCAT (2009) indicates that an estimated 73
percent of the 3.4 billion ha of rangelands, most of which are located in
drylands, worldwide are affected by soil degradation.
Climate change, through its effects on desertification that has resulted in
the loss of 12-18 billion tons of carbon, is predicted to have even a more
significant impact on these impoverished and vulnerable but important
ecosystems (Muñoz-Rojas et al., 2012a; 2012b; 2013). It is feared that,
if continued unabated, climate change and variability will continue to pose
serious threats to the often vulnerable and impoverished people living in
these hostile environments and their livelihood assets, the livestock. On
the other hand, there are evidences (e.g. United Nations, 2011;
FAO/LEAD, 2006; IPCC, 2007) that show that these areas might play a
key role in mitigation of climate change effects through their great
potential for sequestration of carbon in soils and living vegetation. Since
carbon losses from drylands are associated with loss of vegetation cover
and soil erosion, management interventions that slow or reverse these
processes can simultaneously achieve carbon sequestration and, thus,
help in climate change mitigation. Thus, reversing land degradation in
extensive
dryland
areas through improved pasture
and rangeland
management would contribute to restoring the soil and vegetation carbon
sink while also improving livestock-based livelihoods.
As a result, the potential of extensive areas of semi-arid and arid
rangelands to sequester C has been receiving increasing attention
because of the very large global extent of such environments (Glenn et
al., 1993; Conant et al., 2001; Howden et al., 2001; Moore et al., 2001;
Burrows et al., 2002; Dener et al., 2006; Harper et al., 2007). Efforts
have been and are being made to estimate carbon sequestration potential
of the drylands by several workers (Smith et al., 2008; Lal, 2001, 2003,
2004; Campbell et al., 2008; UNEP, 2008; IPCC, 2001; White et al.,
2000; Grace et al., 2006; Squires et al., 1995; Keller and Goldstein,
1998).
Pastoralism in Ethiopia is a direct source of livelihood to more than 7
million people who inhabit the vast lowland and drought-prone territories,
which make up about 40% of the total land area of the country (Helland,
2006). It produces 80% of the total annual milk supply (CAPE OAU/IBAR,
2014) and contributes 19% of the GDP with annual returns to capital from
livestock (through the production of milk, meat, skin, hides, etc)
estimated at around 2.1-2.6 billion USD (Behnke, 2010). This makes the
sector an important source of indigenous livestock for export markets and
urban consumption.
Given the size of the C pool in grazing lands, it is important to improve
understanding of the current and potential effects of grazing land
management on soil carbon sequestration and storage (Schuman et al.,
2002). There is, therefore, a growing interest in assessing the carbon
sequestration potential of such strategies quantitatively. Real and
accurate carbon data is scarce. Much of the available data is often based
on limited assessment of carbon stocks in a specified range unit, which
fails to capture the spatial and temporal heterogeneity that characterizes
pastoral ecosystems (Dabasso et al., 2014).
Furthermore, limited data regarding soil carbon (C) sequestration
potential
and
biosequestration
potential
in
arid
and
semi-arid
environments is an impediment to appropriate policy formulation directed
at greenhouse gas abatement (Witt et al., 2011). Also, unavailability of
such data has resulted in exclusion of carbon accumulation in grazing
lands from existing international carbon trading mechanisms, such as the
Clean Development Mechanism. Such carbon stock data can, therefore,
provide baseline information to determine if pastoral grazing management
can be engaged for carbon credit trading.
Nevertheless, the carbon stock and carbon sequestration potential of the
extensive grazing areas in pastoral and agro-pastoral areas of Ethiopia
has not been assessed in a comprehensive way. Furthermore, impacts of
participatory rangeland management practices on carbon stock of grazing
systems have not been evaluated. It is imperative to generate such
quantitative information in order to provide evidence-based guide to
policy decisions in pastoral areas.
1.2. Overall Objectives and Expected Result Linkage
The research was conducted with the following main objectives:
 Assess the status of carbon stock of rangelands in PRIME intervention
clusters and their contribution to climate change mitigation,
 Compare the carbon stock of selected managed and unmanaged
rangelands and its implication to climate change mitigation, and
 Extract policy briefs that will direct policy makers on rangeland
management in pastoralist areas for climate change mitigation
2. METHODOLOGY
2.1. General Description of the Study Areas
The study was conducted in selected PRIME intervention areas of East,
Afar and South clusters during 2014. The East cluster is primarily found in
Ethiopian Somali Region and Babile woreda of Oromia Region; the Afar
cluster denotes the Afar Region and the South cluster encompasses
pastoral areas of Borena and Guji zones of Oromia Region. From the East
cluster four grazing systems (Harshin, Daketo, Mulu, and Afdem) were
selected. From the Afar cluster, three grazing systems, namely Mollale
(Gewane), Halydege, and Dudub were selected for the study. Similarly,
from the South cluster Malbe and Dire from Borena zone, and Dida Dheda
and Golba Genale grazing systems from Guji zone were considered. The
selected grazing systems, the sub-systems within them, and important
features of the specific sites from where samples were collected are
discussed under each system. Figure 1 shows the location of sampling
sites at different grazing systems in the three clusters.
Figure 1 Location map of sampling sites at the different grazing systems
in the three clusters.
2.2. Sampling Site Selection
Sites for collection of vegetation and soil samples were selected
systematically in consultation with None Governmental Organizations
(NGOs) operating in each grazing systems. To this end, the study sites in
the East cluster were selected together with AVECO and ACPA. In Afar
cluster, sites were selected in consultation with CARE Ethiopia. Grazing
systems in South cluster were selected jointly with CARE and MERCY
CORPS. As there was no information about the size of the grazing
systems and sub systems, the sample plots were located randomly taking
into account differences in topography and vegetation type within the
selected sites in the systems.
Since there were no grazing systems that were put under protection
before this study in East and Afar clusters, only three sites from Borena
and Guji zones were used for comparison of carbon stock under protected
and unprotected grazing lands. One of these (Dida Haya in Sarite from
Malbe) was under traditional system of rangeland protection called the
Kallo system, while the remaining two (Andereka in Meesa and Haro
Areero in Siminto) were under participatory rangeland management
scheme for the last 3 to 4 years. Table 1 describes some basic features of
the sampling sites within the selected grazing systems.
Table 1. Study sites selected for carbon stock assessment and their basis
characteristics
Cluster
Grazing
system
Harshin
Hussein
Samane
Plot No.
Special characteristics
1
Heavily degraded grazing land
with
patches
of
perennial
grasses
Heavily degraded rangeland with
patches of perennial grass and
shrub
Forest land with no undergrowth
Upper part of Daketo valley
dominated
by
cactus
and
Lanthana camara
Lower part of Daketo valley and
wetland covered by grass and
annual herbaceous plants
Mixed grazing land with acacia
trees, cactus and perennial
grasses
Mixed grazing land with acacia
trees, cactus, shrubs, and grass
Mixed grazing land with Acacia
and perennial grasses bordering
Ethiopian Somali and Oromia
regions
Open grazing land dominated by
perennial grasses and patchy
2
Elbahi
3
4
Elbahi
5
Jejeba
6
Kulmeye
7
Mencha
8
Siselu
9-11
East
Daketo
Sub-system
Mulu
Afdem
Cluster
Grazing
system
Mollale
Bonketto
Afar
Halydege
Dudub
Sub-system
Plot No.
Dire Ella
12
Mollale
13
Gonita Birka
14
Halydege
Village
15
Andido
16
Motor Sefer
17
Irribeto
18
Hudud
Elwaye
Arbela)
(Dida
19
18-19
(Dida
20-21
Malbe
South
Elwaye
Haya)
Soda
22
Dida Medhicho
23
Dubluk
24
Dire
Siminto
Golba
Genale
Miessa
plots)
(two
25-27
Siminto
plots)
Muche
Guduba
Bururie
(two
28-29
30
31
Special characteristics
bushes
Stony and heavily degraded with
scattered acacia trees
Newly cleared from Prosopis
juliflora
An open grazing land with
encroaching
prosopis
and
perennial
grass
production
potential
Degraded grazing land with
patches of perennial grasses and
scattered prosopis plants
Vast grazing sub system devoid
of vegetation with cracking soil
type
Degraded, stony and scattered
Acacia trees
An area newly cleared from
Prosopis and have scattered
bushes
Have sparsely distributed bush
Vast
grazing
system
with
perennial and annual grasses
and wildlife potential
Protected
and
unprotected
grazing land
Mixture of grass and woody
perennials with wildlife potential
Protected
area
with
good
regeneration of grass and other
vegetation
Heavily grazed area with wildlife
potential
Rangeland
passing
through
several
phases
(protection,
Damage and again protection)
Rangeland composed of both
protected and unprotected areas
Rangeland with dense vegetation
Rangeland with vegetation
2.3. Field layout for above ground vegetation sampling
A ‘nested’ sampling approach (Hairiah et al., 2011) was followed,
assessing large diameter trees (with a stem diameter above >30 cm) in
rectangular plots of 100 m x 20 m, and trees and shrubs with DBH 2.530 cm in subplots of 40 m x 5 m. As there were no big trees with DBH >
30 cm, samples were taken from a rectangular plot of 40 m X 5 m. All
trees and shrub with DBH and height of trees greater than 2.5 cm within
the 40 m X 5m plot were recorded on pre-prepared registration sheet. A
1m X1m quadrat was laid at the four corners and center of the 40 m X 5
m plot for herbaceous plants, undergrowth vegetation and litter sample
collection. All herbaceous plants and woody undergrowth vegetation with
DBH < 2.5 cm were cut at the ground level and their fresh weight was
measured together with litter collected from the same plot using weighing
balance. A sub-sample of 300 g fresh mass was taken from the composite
sample for laboratory analysis. The samples were oven dried at 80 ⁰C for
24 hours until the mass of the sample remained constant. The diameter of
trees was measured using caliper, while the height was measured using
clinometer.
2.4. Estimation of vegetation carbon stock
The following allometeric equation was used to estimate the aboveground
biomass and carbon stock of trees:
ABGTB (kg tree1 )  exp 1.996  2.32l(D)
[1]
where: ABTB = aboveground tree biomass; D = diameter of tree
Then after, the carbon stock was calculated as:
C s toc k 
Biomass
2
[2]
Estimation of carbon stock of root biomass
Non-destructive (conservation) method was employed for calculation of
carbon stock in the root system. As suggested by Santantonio et al.
(1977) and MacDicken (1997), the below ground biomass (root) of a plant
is close to 20 percent of the total aboveground biomass. Accordingly, the
root biomass of trees was estimated using the following formula:
BGB  0.20  AGB
[3]
where BGB is below ground biomass, AGB is above ground biomass
Total carbon stock = Carbon stock of above ground biomass + Carbon
stock of below ground biomass
2.5. Soil Sampling and Preparation for Soil Carbon Stock
Assessment
Soil samples were collected from the four corners and center of the 40 m
X 5 m plots from 0-10, 10-20, and 20-30 cm depths and mixed
thoroughly on an aluminum tray to make one composite sample per depth
per plot. Accordingly, three composite samples were collected per plot for
laboratory analysis of soil organic carbon. The collected samples were
properly labeled and transported to Haramaya University Soil Science
laboratory.
The samples were then air-dried by spreading them on paper in a
ventilated soil sample preparation room. The total mass of the air-dried
samples was recorded before crushing the samples to pass them through
a 2 mm sieve diameter. Visible coarse fragments, such as gravel, were
separated before crushing the samples. Following this, the samples were
gently crushed with mortar and sieved. The mass of the coarse fragments
that did not pass through the 2 mm sieve and those that were separated
before grinding were recorded for each sample.
Undisturbed soil samples were also collected from the respective depths
using soil cores that were inserted into a metallic cylindrical core that is
prepared for this purpose. For all the plots, the undisturbed samples were
collected from centers of the plots only.
The soil organic carbon content was determined following the WalkleyBlack oxidation method (Walkley and Black, 1934). The dry bulk density
of the soils was determined using the core method as described in Blake
and Hartge (1986) in which case the core samples were dried in an oven
set at a temperature of 105 C to a constant weight. The dry bulk density
was calculated using the following equation:
BD(g/cm3 ) 
MO DS(g)
Vt (cm3 )
[4]
where:
MODS
=
mass of the oven-dry soil (g)
Vt
=
total volume of the soil core calculated from:
Vt  πr 2h
r is the internal radius of the cores measured using a caliber (cm), and h
is height of the cores measured using a hand tape. After oven drying the
core samples, any coarse fragment that did not pass through the 2 mm
sieve diameter was separated and the fine earth (< 2 mm) weighed and
used as mass of the oven dry soil.  is a constant which is equal to 22/7.
2.6. Estimation of Soil Carbon Stock
The organic carbon content of soils obtained from laboratory analysis was
used to calculate carbon stock per unit area of land. The carbon stock for
each layer per hectare was calculated as:
Ci (ton/ha)  BDi 1  CFi  di  OCi 10
[5]
where:
BDi
=
bulk density of the ith layer (i =1-3) (kg/m3)
CFi
=
coarse fragment content of the ith layer (fraction)
di
=
thickness of the ith layer (m)
OCi
=
organic matter content of the ith layer (fraction)
10
=
conversion factor from kg/ha to ton/ha
The total carbon stock for the 0-30 cm depth was calculated as:
3
C tot (t/ha)   Ci
i1
[6]
2.7. Estimation of Terrestrial Carbon Stock and Carbon
Dioxide Equivalent
Finally, the terrestrial (total) carbon stock (ton/ha) of a given site was
obtained from:
Ctotalstock  Csoil  CA GWV  CHV  CBGB
[7]
where:
Csoil
=
soil carbon stock
CAGWV
=
carbon stock of above-ground woody vegetation
CHV
=
carbon stock of herbaceous vegetation
CBGB
=
carbon stock of below ground biomass
As 1 tone of soil OC = 3.67 (44/12-ratio of molecular weight of CO2 to
carbon) tons of CO2 (sequestered or emitted) (Pearson et al., 2007; Craig
et al., 2010), the equivalent CO2 sink (tons/ha) in a given site was
estimated from:
CO2e  3.67 * Ctotal
[8]
3. KEY FINDINGS
The results obtained from field measurement and laboratory analysis are
discussed on grazing system basis. Furthermore, comparisons among
carbon stock of sub-systems within a grazing system is made. The
detailed discussions are presented here under.
3.1. East Cluster
3.1.1. Terrestrial Carbon Stock of Harshin Grazing System
3.1.1.1. Overview of the grazing system
Harshin grazing system is found in Harshin Woreda of the Somali Regional
State of Ethiopia. Harshin is bordered on the south by the Degehabur
zone, on the west by Kebri Beyah, and on the northeast by Somalia.
According to the 2007 census, the total population of the Woreda was
80,244 of which about 49% were pastoralists (CSA, 2007). The Woreda is
inhabited by the Arap and Habar Awal subclans of the Somali Isaac clan.
The Hussein Semane sub-system was selected as it was believed to be
representative of the whole grazing system and has high potential for
rehabilitation and/or change. The sub-grazing system comprises of
grassland, grass land mixed with patches of herbaceous shrub locally
called Gahadi, and woody vegetation dominated by acacia species of
different types. The dominant livestock in the area are sheep, goats, and
camel. The grassland is highly degraded due to overgrazing. As a result,
there are places with only bare soil. The woody vegetation is also devoid
of any undergrowth. The understory is completely bare soil with no other
vegetation type of any sort. Plate 1 indicates the partial view of the three
sampling sites, the nature of their vegetation cover, and the intensity of
grazing.
Plate 1. Partial view of the Hussein Semane sub-grazing system sampling
sites, nature of vegetation cover, and stocking density in Harshin
grazing system.
The soils are mainly sandy loam to sandy clay loam in texture with
relatively high surface bulk density (1.85-1.90 g cm-3) that shows the
existence of compaction. This compaction is the result of repeated animal
trampling. The disadvantage of this high bulk density is its effect on
infiltration of rain water into the soil system. It results in low infiltration
rate and high runoff generation from a given rainfall event. This, in turn,
results in low water storage in the soil system for plants. Furthermore,
the soils are strongly alkaline (Tekalign, 1991) in reaction with pH that
ranged from 8.75 to 8.92. Soils with such a high pH are likely to contain
excess amount of sodium on the exchange complex. This cation has
unfavorable effect on soil structure resulting in dispersion of soil
aggregates. The high bulk density could be related to this dispersion in
addition to the effect of repeated animal trampling.
Three sample plots were laid in the sub-grazing system based on
differences in vegetation and topography. The first plot was laid on a
heavily degraded grazing land with patches of perennial grasses. The
second plot was on a heavily grazed but with patches of perennial grasses
and a shrub locally called Gahadi, which is browsed mostly by camel. The
third plot was laid within the woody forest of the sub-grazing system.
Unlike most woody forest based grazing systems, the Hussein Semane
sub-grazing system is devoid of undergrowth vegetation and grasses.
The sample collection was done during April, 2014, which was a rainy
season for almost large part of the Somali region.
3.1.1.2. Results and discussion
The terrestrial carbon stock of the Hussein Semane sub-system is
indicated in Table 2. In the first two sites with mainly degraded grassland,
significant proportion of the carbon stock (99.99%) was contributed by
the soil. On the other hand, at the site with woody forest, the vegetation
contributed for 44.15% (46.08 t ha-1) of the terrestrial carbon stock,
while the soil carbon stock accounted for 55.85% (58.29 t ha-1) of the
total carbon stock for the sub-system. The carbon dioxide equivalent
(CO2e), which indicates the carbon dioxide emitted or sequestered,
ranged from 208.951 at the second site with degraded grass and patches
of herbaceous bush to 383.038 t ha-1 at the woody forest site.
Since it was not possible to find the total area of the Harshin grazing
system, it was not possible to estimate the total terrestrial carbon stock
and its CO2e for the whole system. However, it is possible to put an
average value for the whole system based on the results obtained from
this baseline assessment. Accordingly, the baseline mean terrestrial
carbon
stock
of
the
Harshin
grazing
system
can
be
taken
as
73.924±26.426 t ha-1 with coefficient of variation of 35.75%, which
actually indicates the existence of high variability within the system.
Similarly, the corresponding mean CO2e of the system can be taken as
271.301±96.984 t ha-1.
The results obtained clearly indicate the contribution of the soil and
vegetation sinks and their relative importance. As it has always been true,
combined management of both soil and vegetation would contribute for
better carbon sequestration and, thus, climate change mitigation.
Table 2. Terrestrial carbon stock and its carbon dioxide equivalent (t ha-1)
at the Hussein Semane sub-grazing system in Harshin, Somali
region
Plot
AGW HV
V
1
0.004
2
0.003
3
38.4
Mean ±StD
Carbon stock (t ha-1) in
BGB
Soil
Total
0.003
0.002
7.68
60.46
56.93
58.29
58.56±1.78
60.467
56.935
104.37
73.924±26.426
CO2e (t ha-1)
221.914
208.951
383.038
271.301±96.984
AGWV = above-ground woody vegetation; HV = herbaceous vegetation; BGB = belowground biomass; StD = standard deviation
The contribution of the soil varied with soil depth (Figure 2). At all the
three sites, the carbon stock consistently decreased with soil depth.
Nevertheless, the difference was the highest at site 1 compared with the
other two. This could be attributed to the fact that, in grasslands, most of
the contribution is limited to the upper few centimeters of the soil. The
CO2e also varied in accordance with the variation in soil organic carbon
stock. Nevertheless, the variability in soil carbon stock among the three
sites was relatively low with a coefficient of variation of 3.04%.
The results indicate that management of grazing systems in pastoral
areas could enhance the carbon sequestration potential of both soil and
vegetation. The improvement will help in mitigating climate change
impacts through directly reducing the amount of CO2 emitted from these
systems and indirectly improving the productivity of both vegetation and
soil.
Figure 2. Carbon stock and CO2e (t ha-1) variation with soil depth at the
Hussein Semane grazing sites in Harshin grazing system,
Somali region (HS = Hussein Semane).
3.1.2. Terrestrial Carbon Stock at Daketo Grazing System
3.1.2.1. Overview of the grazing system
The Daketo grazing system is located within Babile woreda of Ethiopian
Somali Region and Babile woreda of Oromiya region, thus connecting two
regional states. Babile woreda, which is part of the Jijiga zone, is
bordered on the west by the Oromia region, on the north by Gursum, and
on the east and south by Fiq zone. Census conducted in 2007 indicates
that the Woreda has a total population of 77,317, of 22.68% are
pastoralists. The Woreda is inhabited by the Karanle Hawiye clan of the
Somali people, as well as the Babille Oromo.
However, this study was conducted in Babile woreda of Ethiopian Somali
region in the Daketo valley and its surrounding called Elbahey. The upper
part of the valley is covered with cactus and Lanthana camara vegetation
with poorly growing annual grass. The valley bottom, on the other hand,
is a marshy area covered with perennial grasses and herbaceous
vegetation of different types. Samples were collected from two separate
plots one each at the upper and lower (valley) parts of the Elbahey subsystem. Plate 2 shows the nature of vegetation at the two sampling sites.
A
C
B
D
Plate 2. Partial view of the Elbahey sub-grazing system in Daketo; A and
B show the upper smapling plot dominantly occupied by cactus
and Lanthana camara, and B and C show the second sampling
site in Daketo valley with annual herbaceous vegetation.
The soils of the area had high bulk density values, which ranged from
1.90-1.93 g cm-3 at the surface 0-10 cm soil depth to 1.95-2.01 g cm-3 in
the subsurface layers, which indicate the presence of high compaction. As
already stated, this high compaction, caused presumably by repeated
animal trampling, is likely to affect the water economy of the root zone by
increasing runoff and reducing infiltration into the soil system. This is a
disadvantage in pastoral areas where rainfall is most of the time torrential
and erratic in its distribution. The textural class of the soils ranges
between loamy fine sand and sandy clay, which also indicates the
inherently low water holding capacity of the soils. On the other hand, the
pH of the soils (8.23-8.35) indicates the strongly alkaline nature of the
soils (Tekalign, 1991).
The main livestock kept are a mixture of camel, goats, sheep, and cattle.
Furthermore, significant area of this system is under crop production. In
this system, therefore, both pastoralism and agro-pastoralism are being
practiced.
3.1.2.2. Results and discussion
At both sites, there were no woody vegetation to be sampled. The results
indicate that the contribution of the herbaceous vegetation, as compared
to that of the soil, was almost insignificant. Accordingly, at the upper part
where cactus and Lanthana camara are the dominant vegetation cover,
99.998% (120.49 t ha-1) of the carbon stock was from the soil sink. This
clearly indicates the importance of the soil as a carbon sink in this
degraded grazing system. At the valley where the second site is, the
trend is almost the same in that 99.997% (59.91 t ha-1) of the organic
carbon is stored in the soil (Table 3). Comparing the two sites, the site
dominantly covered by cactus and Lanthana camara had by far the largest
carbon stock than that covered by herbaceous vegetation and grass. This
might be attributed to the intensive grazing, particularly by cattle, of the
herbaceous vegetation and grass, which leaves very little organic input
into the soil system. Furthermore, the Daketo valley is a grazing system
that most pastoralists in the area use during the dry season.
The corresponding CO2e ranged from 219.881 t ha-1 in the valley to
442.209 t ha-1 in the upper part of the sub-grazing system. The Daketo
grazing system is a very extensive system dominated mainly by sparsely
populated trees of acacia species, cactus and Lanthan camara. The
topography of the system is also characterized by hills and valleys with
extensive rock outcrops covering the hills. The two plots are assumed to
represent majority of the grazing system, though.
The variation of the carbon stock followed almost consistent trend with
soil depth at the upper part of the grazing system, while it remained
equal in all the depths in case of the grazing system in the valley (Figure
3). The top 10 cm of the soil layer seems to store most of the organic
carbon stock. This might be attributed to the distribution of organic
matter sources in the soil system. Furthermore, there was high variability
in organic carbon stock between the two soils with a coefficient of
variation of 47.49%. This indicates that the relatively high terrestrial
carbon stock variability within the Daketo system is mainly due to
differences in soil carbon stock.
On the basis of this assumption, therefore, the baseline carbon stock of
the system was taken as 90.203±42.837 t ha-1 with coefficient of
variation of 47.49%, which also shows the high variability within the
system. The corresponding baseline mean CO2e of the system was
331.045±157.210 t ha-1.
Table 3. Terrestrial carbon stock of the Elbahey grazing sub-system in
Daketo grazing system of Somali region
Plot
Carbon stock (t ha-1) in
CO2e (t ha-1)
AGWV
HV
BGB
Soil
Total
1
0.002
0.001
120.49
120.493
442.209
2
0.002
0.001
59.91
59.913
219.881
Mean±StD
90.20±42.837 90.203±42.837 331.045±157.210
AGWV = above-ground woody vegetation; HV = herbaceous vegetation; BGB = belowground biomass; StD = standard deviation
The results indicate that even the highly degraded grazing lands in
pastoral areas have significant carbon stock in them. Rehabilitation of
such grazing systems through, for instance, participatory rangeland
management approach could enhance their carbon sequestration potential
further. This will help create climate change resilient ecosystems that
support the livestock better and improve the livelihood of the pastoral and
agro-pastoral community in the area.
Figure 3. Carbon stock and CO2e (t ha-1) variation with soil depth for
selected grazing sites in Dakato grazing system (EBL = Elbahey
bush land; EGL = Elbahey graa land).
3.1.3. Terrestrial carbon stock of the Mulu grazing system
3.1.3.1. Overview of the grazing system
The Mulu grazing system is located in Meiso Woreda, which is located at
the westernmost point of the former Shinile zone, now Ayisha zone. The
Woreda shares boundaries with Oromia region on the south, Afar region
on the northwest, and Afdem woreda on the east. Based on figures
published by the CSA in 2005, this woreda has an estimated total
population of 53,665. This Woreda is primarily inhabited by the Issa clans
of the Somali people. Although the exact figure is not known, both
pastoralism and agro-pastoralism are being practiced in the Woreda.
The Mulu grazing system comprises of Jejeba, Kulmeye and Mencha subgrazing systems. All the sub-systems are characterized by the presence of
a mixture of trees dominantly of acacia, shrubs, cactus, grasses and other
herbaceous vegetation. The system supports cattle, shoats and camel.
Limited large-scale crop production is also being practiced. However, in
terms of vegetation cover, it is in a better condition with relatively well
protected vegetation cover. Plate 3 shows nature of the vegetation cover,
data and sample collection activities at the three sub-grazing systems in
Mulu grazing system.
Plate 3. Nature of vegetation, vegetation data (measuring tree diameter
and weighing fresh biomass of herbaceous vegetation),
vegetation and soil sample collection activities at the three
grazing sub-systems in Mulu grazing system.
The textural classes of the soils within the system are between sandy clay
loam and clay loam with relatively better clay content. The bulk density
values in the grazing system ranged from 1.86-1.88 g cm-3 at the top 10
cm layers to 1.86-1.98 g cm-3 at the subsurface layers. Similar to the bulk
density values discussed above, these bulk density values are also in the
range that shows the existence of soil compaction in these grazing
systems. The pH values (8.42-8.62) indicate the saline nature of the soils
in all the three grazing sub-systems. Only plants that are tolerant to such
extremes can thrive better. Salinity management seems relevant for
adapting wide range of grass species in those grazing systems if artificial
seeding is envisaged.
3.1.3.2. Results and discussion
At Mulu grazing system, both vegetation and soil contributed to the
terrestrial carbon stock of the system. On the basis of this, 18.875,
20.895, and 23.605% of the terrestrial carbon stock at Jejeba, Mencha,
and Kulmeye, respectively, is stored in the vegetation cover, while the
corresponding carbon stock in the soil was 81.125, 79.105, and 76.395%.
Because of the significant contribution from the vegetation cover, the
terrestrial carbon stock was relatively high. The corresponding CO 2e
ranged from 455.898 t ha-1 at Kulmeye to 660.791 t ha-1 at Mencha.
Table 4. Terrestrial carbon stock at three grazing sub-systems in Mulu
grazing system, Somali region
Site
Carbon
HV
0.002
0.002
0.003
stock (t ha-1) in
CO2e (t ha-1)
AGWV
BGB Soil
Total
Jejeba
27.89
5.58
143.86
177.332
650.808
Mencha
31.35
6.27
142.43
180.052
660.791
Kulmeye
24.43
4.89
94.90
124.223
455.898
Mean±StD
127.063±27.863 160.536±31.477 589.166±115.521
AGWV = above-ground woody vegetation; HV = herbaceous vegetation; BGB = belowground biomass; StD = standard deviation
The results obtained here also indicate the existence of high potential for
carbon sequestration in pastoral areas if proper management scenario is
put in place.
Depth-wise distribution of the soil carbon stock indicates that, at all the
three sub-systems, the organic carbon stock of the soils decreased
consistently with soil depth (Figure 4). At system level, the mean soil
carbon stock was 127.063±27.863 with a coefficient of variation of
21.93% which indicates the presence of moderate variability among soils
within the grazing system.
Figure 4. Carbon stock and CO2e (t ha-1) variation with soil depth at
selected grazing sites in Mulu grazing system (ME = Mecha; KL
= Kulmeye; JJ = Jejeba).
Similar to the other grazing systems in the East cluster, it was not
possible to get the total area covered by the Mulu grazing system. As a
result, it was not possible to estimate the baseline carbon stock of the
system. However, it is possible to derive a mean value for the system
based on measurements made in these three representative sub-grazing
systems. Accordingly, the mean baseline terrestrial carbon stock of the
system can be taken as 160.536±31.477 t ha-1 with coefficient of
variation of 19.61%, which indicates the existence of relatively low
variability in the system. Similarly, the corresponding baseline mean CO 2e
of the system can be taken as 589.166±115.521 t ha-1.
3.1.4. Terrestrial Carbon Stock of the Afdem Grazing System
3.1.4.1. Overview of the system
Afdem is located in the former Shinile Zone, now Ayisha Zone, of Somali
region of Ethiopia. It is bordered by Mieso on the southwest, Afar region
on the north, Erer on the east, and Oromia region on the south. There are
some high peaks (e.g. Mount Afdem about 2000 meters above sea level)
in the Woreda. According the results of the 2007 Census, the total
population of the Woreda is around 65,031. Out of this total population,
76.54% are pastoralists. The Woreda is inhabited by the Issa clan of the
Somali people.
The Afdem grazing system, particularly the Dire Ella around the Afdem
town, is more degraded compared to the adjacent Mulu grazing system in
terms of its woody perennial composition. Dire Ella sub-systems is highly
degraded with sparsely distributed Acacia bush and open grassland. The
understory is highly degraded with almost no vegetation cover. On the
other hand, the Siselu sub-system is a very extensive grass land with
sparsely distributed herbaceous bushes and woody vegetations of
different species. The common livestock in the system are shoats, camel,
and cattle. Plate 4 below shows the degraded nature of both vegetation
and soil at Dire Ella (upper) and, degraded grass land and the heavy
overgrazing at Siselu (bottom) in Afdem grazing system.
Plate 4. Partial view of the highly degraded vegetation and soil in Afdem
grazing system at Dire Ella and Siselu, and the livestock that are
desperate to get some feed from these highly degraded grazing
lands.
The textural class at Dire Ella is loamy fine sand with high proportion of
sand. This high proportion of sand indicates the likely poor water holding
capacity of the soils, and, thus, more vulnerability to moisture deficit
stress. Nevertheless, the textural class at the Siselu site is sandy loam at
all the three sites and depths, indicating the uniformity of the soil in the
sub-system. The bulk density values, unlike those recorded in the other
grazing systems, ranged from 1.30 g cm-3 at Siselu to 1.78 g cm-3 at the
surface layers, and 1.29 g cm-3 at Siselu to 1.97 g cm-3 at Dire Ella in the
subsurface layers. The bulk density values at Siselu are within acceptable
bulk density ranges for mineral soils, while those at Dire Ella, particularly
those in the subsurface layers, indicate the existence of some degree of
compaction. The pH of the soils at Dire Ella, like the other systems, was
high (> 8.5), which indicates the strongly alkaline nature of the soils. The
pH ranges indicate the possible dominance of exchangeable sodium on
the exchange complex of soils in Dire Ella sub-system. On the other hand,
the pH values at Siselu ranged from 7.2-7.9 at the surface layers, and 7.4
to 7.8 in the subsurface layers, which fall in the range of neutral to
moderately alkaline (Tekalign, 1991).
3.1.4.2. Results and discussion
The terrestrial carbon stock in the Afdem grazing system varied from
50.210 t ha-1 at grass dominated Siselu 1 sub-system to 67.855 t ha-1 at
Dire Ella (Table 5). Similar to the trends observed in the other grazing
systems, the proportion of the total carbon stock stored in the soils was
generally higher than that in the vegetation. The equivalent carbon
dioxide sequestered ranged from 184.271 t ha-1 at Siselu 1 to 249.028 t
ha-1 at Dire Ella.
Table 5. The terrestrial carbon stock and its carbon dioxide equivalent at
two grazing sub-systems in Afdem grazing system, Somali
region
Carbon stock (t ha-1) in
Site
CO2e (t ha-1)
AGWV HV
BGB
Soil
Total
Dire Ella
15.46 0.005
3.09
49.30
67.855
249.028
Siselu 1
50.21
50.210
184.271
Siselu 2
0.003 0.002
65.38
65.385
239.963
Siselu 3
0.005 0.003
51.03
51.038
187.309
Mean±StD
53.98±7.633 58.622±9.296 215.143±34.118
AGWV = above-ground woody vegetation; HV = herbaceous vegetation; BGB = belowground biomass
The carbon stock increased with soil depth consistently at both the
grazing sub-systems (Figure 5). The results obtained so far indicate the
relative importance of the upper 10 cm of the soil layer as carbon sink. At
system level, the mean soil carbon stock was 53.980±7.633 which shows
relatively narrow variation as was also indicated by the low coefficient of
variation (14.14%).
The results obtained in this system also clearly revealed the carbon
sequestration potential of even the relatively degraded grazing systems
such as the Afdem system. The mean carbon stock for this system can be
taken as 58.622±9.296 with relatively low variability as indicated by the
coefficient of variation (15.86%). The corresponding baseline mean
carbon dioxide equivalent is 215.143±34.118 t ha-1.
Figure 5. Variation of soil carbon stock and the corresponding CO2e with
soil depth at selected grazing sub-systems in Afdem, Somali
region (DE = Dire Ella; SS = Siselu).
Comparison of the four grazing systems selected in the East cluster
indicates that the status of terrestrial carbon stock and the corresponding
CO2e was relatively high at Mulu grazing system followed by Daketo and
Harshin systems (Figure 6). The Afdem system, being relatively the drier
system, was found to be low in its terrestrial carbon stock and the
corresponding carbon dioxide equivalent. Nevertheless, the variability of
the terrestrial carbon stock was the highest in the Daketo grazing system
followed by the Harshin grazing system. This may imply that the number
of sampling sites need to be increased in order to get representative
value of carbon stock. On the other hand, the variability of the terrestrial
carbon stock was relatively low at Mulu and Afdem grazing systems.
Figure 6. Mean terrestrial carbon stock and its carbon dioxide equivalent
(t ha-1) at four pastoral area grazing systems in Somali region.
In addition to helping in mitigating climate change effects through carbon
sequestration, the pastoral areas can also be sources of income from the
carbon finance. Using the rate used by Ethiopian Wildlife Authority (Daan
et al., 2012), which suggests a currency value of $4/tCO2e, the monetary
value of the mean carbon dioxide sequestered in each of the grazing
systems will be 1085.18, 1324.16, 2356.67, and 905.88 US$ ha-1 for
Harshin, Daketo, Mulu, and Afdem grazing systems, respectively. This is a
huge amount of money which can be used for infrastructure and other
livelihood improvement interventions in those pastoral areas. The
management of these grazing systems, following participatory approach,
will undoubtedly improve the carbon sequestration, productivity of the
grazing systems and livestock, and eventually increase the resilience of
the pastoral community to climate change and variability impacts.
3.2. The Afar Cluster
The pastoralist community in Afar region makes up about 90% of the
total population with remaining 10% being agro-pastoralists. This clearly
indicates the importance of pastoralism in the region. In the Afar cluster,
three grazing systems were selected based on discussion held with the
local partners and government offices. These systems were Gewane,
Halydege, and Dubdub grazing systems. Brief background of each of
these systems is presented below together with the results.
3.2.1. Terrestrial carbon stock of Gewane Grazing System
3.2.1.1. Overview of the grazing system
Gewane is among the woredas in Afar region and forms part of the Zone
3. It shares boundaries with Amibara in the south, Bure Mudaytu and
Zone 5 in the west, and Somali region in the east. This Woreda is where
Mount Ayalu (2145 meters above sea level) and Mount Yangudi are found.
It also includes water bodies such as Lake Kadabassa which lies in the
swampy lowlands that stretch alongside the Awash River and serve as an
important pasture for pastoralists. The Yangudi Rassa National Park is
also found in the northeastern part of the Woreda. The Woreda has a total
population of 31,318 (CSA, 2007) with no reliable estimate of the
pastoralist community.
The Mollale sub-system was selected from the Mollale Erribeto garzing
system in this Woreda. At the time of sampling, the area was recently
cleared from Prosopis juliflora, the major vegetation cover in the area,
hence there was no undergrowth vegetation and trees to be measured.
The surface was covered by a bare soil that contains no remains of
herbaceous vegetation cover. The measured carbon stock was, therefore,
only that present in the soil. There were extensive wide and deep cracks
that are closely spaced. Plate 5 clearly shows these features.
Plate 5. The partial view of the Mollale sub-grazing system in Gewane.
Prosopis juliflora is being cleared from this field (bottom) and
the soil was devoid of any other vegetation.
The textural class of the soil ranges from clay loam to clay. This fine
textured nature of the soil could be good quality since it results in high
water retention. The bulk density of the soil ranged from 1.14 g cm -3 at
the surface layer to 1.36 g cm-3 at the subsurface layers. These bulk
density values are below critical values of bulk density for plant growth at
which root penetration is likely to be severely restricted (Jones, 1983).
This might be attributed to shrinking and swelling nature of the soil, which
results in healing the compaction naturally. The major problem of the soil,
however, is the extremely high pH (8.83-9.79) which may limit the
number of adaptable species. Only those species that have the natural
ability to overcome this high pH can survive in this environment. If
artificial seeding is planned, consideration of this problem is important in
adaptable species selection.
3.2.1.2. Results and discussion
As described above, there was no vegetation sample of any kind collected
due to complete coverage by Prosopis juliflora, which was being cleared.
There was also no other herbaceous vegetation due to overgrazing and
dry season of the time. As indicated in Table 6, the carbon stock of the
sub-system was relatively low due to its degraded nature and absence of
vegetation cover. However, the area has an immense potential for
rehabilitation if proper management practices can be put in place. The
issue related to Prosopis juliflora, however, should receive a more serious
attention than ever, for it has completely replaced the native vegetation
cover.
Table 6. Soil carbon stock and its carbon dioxide equivalent at Mollale
grazing sub-system Gewane, Afar region
Site
Molale
Carbon stock (t ha-1) in
AGWV HV
BGB
Soil
33.43
Total
33.43
CO2e (t ha-1)
122.688
The depth-wise distribution of the organic carbon stock followed a
consistent trend with soil depth (Figure 7). This indicates the relative
importance of the top 10 cm of soil in carbon stock management.
Figure 7. Soil carbon stock and its carbon dioxide equivalent distribution
with soil depth at Mollale sub-grazing systems in Gewane, Afar
region.
3.2.2. Terrestrial carbon stock of Halaydege grazing system
3.2.2.1. Overview of the system
The Halydege Grazing System is found in Amibara woreda to the eastern
side of the main road to Djibouti and stretches to mount Assebot.
Amibara is bordered by Awash Fentale Woreda on the south, the Awash
River on the west, Zone 5 on northeast, Gewane woreda in the north,
Somali region on the east, and by Oromia region on the southeast.
Based on the 2007 Census conducted by the Central Statistical Agency of
Ethiopia (CSA), this woreda has a total population of 63,378, of which
10.34% are pastoralists.
Three sub-grazing systems were considered from the Halydege grazing
system namely Gonita Birka, Andido and Halydege near the village. The
Andido sub-system is characterized by extensive area of grazing land that
did not contain any vegetation cover at the time of sampling (dry
season). It looks like a ploughed land. Gointa Birka and Halydege subsystems, on the other hand, are covered by mixed grass, herbaceous
vegetation and non-woody bushes. In these systems also, the area
covered by Prosopis juliflora is quite significant. The dominant native
woody vegetation is mainly acacia of different species. Plate 6 shows
some of the features of the grazing system.
Plate 6. The extensive grazing lands located at the low lying areas in
Halydege were devoid of grass vegetation at the time of
sampling. However, Prosopis juliflora is still proliferating at
some of the sites.
The bulk density values recorded indicate that the soils are not affected
by compaction. The values ranged from 1.28 to 1.40 gcm-3 at Andido,
1.14 to 1.25 gcm-3 at Halydege village, and 1.14 to 1.35 gcm-3 at Gointa
Birka. The textural class, on the other hand, varies between loam, sandy
clay loam, and sandy clay, which indicate the presence of appreciable clay
content. This can be taken as a good quality for quick rehabilitation of the
degraded vegetation, for it results in good water holding capacity.
However, the major limitation to these soils is the strongly alkaline nature
of the soil reaction with pH that ranged between 8.71 and 9.51. This
limits the number of adaptable species in those systems, particularly if
artificial seeding is to be considered.
3.2.2.2. Results and discussion
As described above, the woody vegetation was scant in the system. As a
result most of the carbon stock (99.99% at Halydege village and Gointa
Birka, and 100% at Andido) was stored in the upper 0-30 cm depth of the
soils. Owing to the poor vegetation cover, the carbon stock was relatively
low and ranged from 42.160 t ha-1 at Halydege village to 49.095 t ha-1 at
Gointa Birka. The corresponding carbon dioxide equivalent varied from
154.764 t ha-1 at Halydege to 180.179 t ha-1 at Gointa Birka (Table 7).
Table 7. Terrestrial carbon stock and its carbon dioxide equivalent at the
Halydege grazing system in Afar region
Carbon stock (t ha-1) in
HV
BGB
Soil
0.006 0.004
42.16
Site
CO2e (t ha-1)
AGWV
Total
Halydege
42.170
154.764
village
Gointa Birka
0.003 0.002
49.09
49.095
180.179
Andido
45.62
45.62
167.425
Mean±StD
45.623±3.465 45.628±3.463 167.456±12.708
AGWV = above-ground woody vegetation; HV = herbaceous vegetation; BGB = belowground biomass; StD = standard deviation
The distribution of the carbon stock with soil depth indicates that, at all
the sites, the relatively better contribution was from 10-20 cm depth of
the soils (Figure 8). Except at Andido, the high carbon stock in this layer
was due to the high bulk density value rather than high organic carbon
content. Furthermore, the variability of the soil carbon stock at system
level was relatively low as indicated by the coefficient of variability
(7.59%). The mean value obtained from the three sites can, therefore,
represent the soil carbon stock of the entire system reasonably well.
Figure 8. Soil carbon stock and its carbon dioxide equivalent variation
with soil depth at selected sites in Halydege grazing system,
Afar region (AD = Andido; HG = Halydege; GB = Gointa
Birka).
The baseline mean value of the carbon stock and its carbon dioxide
equivalent
for
the
Halydege
grazing
system
can
be
taken
as
45.628±3.463 and 167.456±12.708 t ha-1, respectively, with coefficient
of variation of 7.59%. This low coefficient of variation indicates that the
variability in carbon stock within the system is relatively low and can be
represented by the mean value reasonably well.
3.2.3. Terrestrial carbon stock of the Dudub grazing system
3.2.3.1. Overview of the system
The Dudub grazing system is located in Awash Fentale woreda. This
Woreda is part of Administrative Zone 3 in Afar region. It shares
boundaries with Oromia region in the south, Amhara region in the west,
Dulecha in the north, and by Amibara in the eastern direction. The Awash
River and its tributary Germama cross this Woreda, which indicate the
potential for practicing irrigation. Nevertheless, significant area of this
Woreda is occupied by the Awash National Park.
According to the 2007 Census, the total population of the Woreda was
29,780 of which only 5.69% were pastoralists (CSA, 2007). More than
55%, according to this Census, were urban inhabitants. In addition to
pastoralism, agriculture is also being practiced in the Woreda.
The carbon stock assessment was conducted in three sub systems namely
Motor Sefer, Irribeto and Hudud. The three sub systems do not have
woody trees. As a result, measurements were made for grass, non-woody
undergrowth vegetation, and soil. Plate 7 shows the nature of vegetation
cover in this grazing system.
Plate 7. Some features of the grazing lands in Dudub grazing system. The
soil is bare except the scattered bushy vegetation cover and is
highly prone to wind erosion.
The bulk density values of the soils were below the critical bulk density
values that are quoted as causing root penetration problems due to
excessive compaction (Jones, 1983) and ranged between 1.25 to 1.33 g
cm-3 at the surface layers and 1.39 to 1.51 g cm-3 at the subsurface
layers. Nonetheless, the soils are dominated by the sand fraction in which
the textural class varied from loamy sand to sandy clay. Such soils are
highly prone to drought due to their poor water holding capacity and high
permeability. The pH of the soils ranged from 8.02 to 8.99, which falls in
the range of strongly alkaline (Tekalign, 1991).
3.2.3.2. Results and discussion
Similar to the previous grazing systems, about 99.99% of the terrestrial
carbon stock was in the soil system at all the three systems. The
herbaceous vegetation was highly degraded and over grazed at the time
of sampling, which was during the dry season. That is why the
contribution from the vegetation was extremely small. Except at the
Motor Sefer sub-system, the carbon stock was very low as compared to
what is recorded in the other systems. The values varied between 16.884
t ha-1 at Irrebeto to 49.836 t ha-1 at Motor Sefer (Table 8). The
corresponding carbon dioxide ranged from 61.942 to 182.898 t ha -1. As
compared to the Gewane and Halydege systems, this is more degraded
rangeland.
Table 8. Terrestrial carbon stock and its carbon dioxide equivalent at the
Dudub grazing system in Afar region
Carbon stock (t ha-1) in
HV
BGB
Soil
Total
0.006 0.004
49.83
49.840
Site
CO2e (t ha-1)
AGWV
Motor
182.913
Sefer
Irrebeto
0.004 0.003
16.88
16.887
61.976
Hudud
0.006 0.004
21.82
21.830
80.116
Mean±StD
29.51±17.77 29.519±17.771 108.335±65.220
AGWV = above-ground woody vegetation; HV = herbaceous vegetation; BGB = belowground biomass; StD = standard deviation
The soil carbon stock did not follow any consistent trend with soil depth at
the Motor Sefer site (Figure 9). At Irrebeto, soil sample collection was
limited to the upper 10 cm depth only due to shallow depth of the soil. At
the Dudub grazing system, there was high variability of the soil carbon
stock as revealed by the high coefficient of variation (60.22%). This
implies, for future studies, the number of sampling sites/grazing subsystems has to be increased in order get a mean value for the system
Figure 9. Soil carbon stock variation with soil depth at selected sites in
Dudub grazing system in Afar region (IR = Irrebeto; HD =
Hudud; MS = Motor Sefer).
The baseline mean terrestrial carbon stock and its carbon dioxide
equivalent for this system can be taken as 29.519±17.771 t ha -1 with
equivalent carbon dioxide of 108.335±65.220 t ha-1 and coefficient of
variation of 60.20%.
Comparison at system level indicates that the baseline mean terrestrial
carbon stock was better at Halydege followed by Gewane grazing system,
while it was the lowest at Dudub grazing system (Figure 10). In terms of
management, therefore, the Dudub grazing system requires more
attention in order to rehabilitate the severely degraded grazing system.
The variability of the terrestrial carbon stock was the highest at the
Dudub grazing system as compared to the Halydege system.
Figure 10. Mean terrestrial carbon stock and its CO2e (t ha-1) at selected
grazing systems in Afar region.
If the carbon dioxide sequestered is changed into monetary value using
the Ethiopian Wildlife Authority rate of US $4/t CO2e, the amount of
money that can be generated from the carbon finance scheme will be
490.75, 669.79, and 433.28 USD per ha of grazing land for Gewane,
Halydege, and Dudub grazing systems, respectively. If the carbon
sequestration capacity of these grazing systems is improved through
management, the amount of money generated from the carbon finance
will obviously increase by many folds. This will help in improving the
livelihood of the pastoral community in many ways.
3.3. South Cluster
The South Cluster is one of the clusters under PRIME project which is
operating in Borona and Guji Zones of Oromiya Regional government.
From this cluster, a total of four grazing systems were considered for this
study. The systems were Malbe and Dire from Borena zone, and Dida
Dheda and Golba Genale from Guji zone. Brief description of the Woredas
in which the grazing systems are found is presented under discussions of
each grazing system.
3.3.1. Terrestrial carbon stock of Malbe Grazing System
3.3.1.1. Overview of the system
The Malbe grazing system is found in Teltele woreda. It is characterized
by hilly and gently sloping topography, and extensive plains. The
vegetation in the system varies depending on the topographic position. In
general, the plain land is mainly dominated by grasses with some brushes
and shrubs, the hills by woody vegetation composed of different species
including Juniperous procera, while the gentle slopes are composed
mainly of acacia of different species. The major grazing areas are the
plains that are dominantly covered by grass. Due to this, the sampling
sites were chosen to be on these plain lands.
Teltele is located in the southwest corner of the Borena zone. It shares
borders with Kenya in the southwest, Sagan River in the west and north,
Yabelo in the northeast, and Dire in the southeast. As stated above, the
altitude of the Woreda ranges from 710 to 1460 meters above sea level;
the landscape consists mainly of lowlands and isolated hills. About 45% of
the land in the Woreda is pastureland, while some 25% is arable. As a
result both pastoralism and crop production are practiced in the Woreda.
The total population of this Woreda, as per the 2007 Census, was 70,501
and the dominant ethnic gropus in the Woreda are the Borena Oromos.
Other ethnic groups residing in the Woreda include the Konso, Arbore,
and Hamer.
From the Malbe grazing system, the Elwaye sub-system was selected in
consultation with local partners and its great potential for rehabilitation.
Samples were collected from Arbala Dida, and Dida Haya in Sarite. Both
sites are grasslands. At Dida Haya, samples were collected from
traditionally protected grassland called Kalo and the adjacent unprotected
land, whereas at Arbala Dida samples were collected from two sites
representing the entire extensive grassland. Vegetation samples collected
were grasses at both the sites. The major livestock in the area are cattle,
shoats and camel. Plate 8 illustrates the status of the grazing sites and
some sampling activities.
Plate 8. The nature of the extensive plain grass land at Arbala Dida
(upper), soil and vegetation sampling activities (bottom left),
and protected and adjacent unprotected grazing land (bottom
last two) at Dida Haya at Elwaye sub-grazing system in Malbe.
Note that the Arbala Dida grazing land is also home to some
wild animals such as ostrich.
The textural classes of the soils range from sandy loam to sandy clay
loam. The bulk density values measured were 1.15-1.20 gcm-3 at the
surface layers, and 1.22-1.37 g cm-3 at the subsurface layers of the
Arbala Dida site. The values recorded indicate that the soils of the grazing
land are not yet affected by compaction or have the ability to heal
themselves from compaction naturally. The soils, as observed during
sample collection, are characterized by shrinking (wide and deep cracks)
when dry and swelling when wet. At the Dida Haya site, the values
ranged from 1.32 to 1.42 g cm-3 at the surface layers, and 1.12-1.40 g
cm-3 at the subsurface layers. The higher bulk density values were
recorded on the unprotected land. The soils generally have high pH
values. Accordingly, the pH values at the surface layer varied from 8.65
to 9.88. The subsurface layers also had very high pH (8.14-9.96) across
the grazing system. In general, the pH of the soils within the Malbe
grazing system falls within the range of strongly alkaline pH (Tekalign,
1991). These high pH values could be detrimental to sensitive plants and
limit the number of adaptable species in the grazing system.
3.3.1.2. Results and discussion
Similar to most other systems discussed so far, the major sink of carbon
in this sub-system (Elwaye) was the soil (Table 9). About 99.99% of the
carbon stock at all the sites was stored in the soil. Moreover, spatial
difference in carbon stock was also observed at the Arbala Dida grazing
site. On the other hand, there was very little difference in carbon stock of
protected and unprotected grass land at Dida Haya. In general, the
terrestrial carbon stock at the Elwaye subsystem, representing the Malbe
grazing
system,
ranged
from
43.564
to
72.446
t
ha-1
with
a
corresponding carbon dioxide equivalent of 159.880 and 265.877 t ha -1,
respectively.
Table 9. Terrestrial carbon stock and its equivalent carbon dioxide at
Malbe grazing system, Borena zone of Oromia region
Carbon stock (t ha-1) in
BGB
Soil
0.0002
43.56
Site
CO2e (t ha-1)
AGWV HV
Total
Arbala
0.004
43.564
159.880
Dida 1
Arbala
0.006 0.0001
55.39
55.396
203.303
Dida 2
Dida Haya
0.006 0.0025
72.44
72.446
265.877
P*
Dida Haya
0.0001
72.44
72.44
265.855
Up
Mean±StD
60.958±14.111 60.962±14.110 223.729±51.785
AGWV = above-ground woody vegetation; HV = herbaceous vegetation; BGB = belowground biomass; StD = standard deviation; P = protected; Up =
unprotected.
The depth-wise variation of the soil carbon stock indicated that its
variation was not consistent with soil depth (Figure 11). This indicates the
importance of all the three layers in storing carbon in the soil system.
Furthermore, there was considerable variability in soil carbon stock within
the system with a coefficient of variation of 23.15%. This variability was
almost the major source of the terrestrial carbon stock within the system
as well.
Figure 11. Soil carbon stock and equivalent carbon dioxide variation with
soil depth at the Malbe grazing system in Borena zone of
Oromia region (AD = Arbala Dida; DH = Dida Haya; P =
protected; up = unprotected).
As can be observed from the values in Table 9, there exists a huge
difference in carbon stock between the two different sites within the
Malbe grazing system. However, as baseline information the mean
terrestrial carbon stock and the corresponding carbon dioxide equivalent
for
the
Malbe
system
can
be
taken
as
60.962±14.110
and
223.729±51.785 t ha-1, respectively, with coefficient of variation of
23.15%.
Both the sites from where samples were collected have very good
potential for fast improvement. Particularly the extensive grazing land at
Dida Haya, can support large number of livestock for long period if
allowed to fully attain its potential through participatory management.
The huge difference in grass cover between the enclosed and intensively
grazed adjacent land at Sarite is a clear indication of the potential the
grazing land has for fast rehabilitation. Nevertheless, grazing of the
protected land should also be taken with caution if some organic carbon
has to be returned to the soil system. If intensive and uncontrolled
grazing is allowed, nothing may return to the soil, thus playing no role in
improving the carbon stock of the soil. Therefore, controlled grazing has
to be practiced. Identical values of soil carbon stock recorded in both
protected and unprotected lands at Sarite are typical evidences of the
effects of intensive and uncontrolled grazing on protected lands.
3.3.2. Terrestrial carbon stock of Dire grazing system
3.3.2.1. Overview of the system
The Dire grazing system is found within Dire Woreda, which is located in
the southern part of the Borena Zone. This Woreda shares borders with
Kenya in the south, Teltele in the west, Yabelo in the north, Moyale in the
east, and Arero in the northeast. The altitude of this Woreda ranges from
750 to over 2400 meters above sea level. A survey of the land use shows
that, of the total area of the Woreda, 14.3% is arable, 47.5% pasture,
17.5% forest, and the remaining 20.7% is considered swampy, degraded
or otherwise unusable. In the Woreda, therefore, both pure pastoralism
and agro-pastoralism are being practiced. The 2007 national census
reported a total population for this Woreda of 73,401 (CSA, 2007).
For the carbon stock study, three sites were selected. These were
Dubuluk grazing sub-system, Rare Chebicha, and Dida Medhecho within
the Soda grazing sub-system. The Dubuluk site is dominantly occupied by
scattered shrubs, bushes, and grass. The Rare Chibicha is also composed
of scattered woody vegetation, dominantly of acacia species, while the
Dida Medhecho is dominantly covered by degraded grass and some
noxious vegetation. Furthermore, the site at Dubuluk is a ‘protected
ranch’ but animals were grazing at the time of sample collection. It is also
home to wild animals such as Zebra. The Rare Chebicha site was also
traditionally protected from grazing during the season, while the Dida
Medhecho is open grazing land. The dominant livestock kept in those sites
are cattle, shoats, and camel. The dominance varies from site to site.
Plate 9 below shows some of the features of the sampling sites in Malbe
grazing system.
Plate 9. Partial view of the three sub-grazing systems and their status of
vegetation cover at the Dire grazing system. Near the hills, the
Dubluk sub-system is home to some wild animals like zebra.
The textural classes are mainly sandy loam, indicating that these soils
contain large proportion of the sand fraction. The bulk density values at
the soil surface ranged from 1.32 g cm-3 at Rare Chebicha to 1.62 g cm-3
at Dubuluk, while the subsurface layer bulk density values varied from
1.37 g cm-3 at Rare Chebicha to 1.57 g cm-3 at Dubuluk. The soil at
Dubuluk was extremely difficult to penetrate at the time of sample
collection and this is reflected in the relatively high bulk density values
recorded at this site. The pH of the soils was also high and ranged from
moderately alkaline (7.4-8.0) to strongly alkaline (> 8.0) (Tekalign,
1991).
3.3.2.2. Results and discussion
Except at Rare Chebicha, the major carbon sink at the Dire grazing
system was the soil (Table 10). At Rare Chebicha, the vegetation cover
contributed about 5.98% of the terrestrial carbon stock, whereas at the
other two sites the soil accounted for 99.99% of the terrestrial carbon
stock. The Dida Medhecho site, dominantly occupied by grass, had
relatively the highest terrestrial carbon stock as compared to the other
two sites. In general, the terrestrial carbon stock within the Dire grazing
system ranged from 61.548 to 101.905 t ha-1. The corresponding carbon
dioxide equivalent, on the other hand, varied between 225.881 t ha-1 at
Dubuluk to 373.991 t ha-1 at Dida Medhecho.
Table 10. Terrestrial carbon stock and its carbon dioxide variation with
soil depth at three sites in Dire grazing system, Borena Zone
Carbon stock (t ha-1) in
BGB
Soil
Total
0.003
61.54
61.548
0.843
79.57
84.638
Site
CO2e (t ha-1)
AGWV HV
Dubuluk
0.005
225.881
Rare
4.22
0.005
310.621
Chebicha
Dida
0.003 0.002
101.90
101.905
373.991
Medhecho
Mean±StD
81.003±20.218 81.697±20.248 303.498±74.312
AGWV = above-ground woody vegetation; HV = herbaceous vegetation; BGB = belowground biomass; StD = standard deviation
Furthermore, the carbon stock and the corresponding carbon dioxide
equivalent in the major carbon sink, the soil, showed spatial variation
with soil depth at a given site (Figure 12). Accordingly, the soil carbon
stock decreased consistently with soil depth at Dubuluk site, while it
showed irregular pattern with depth at Rare Chebicha and Dida
Medhecho.
At
system
level,
the
mean
value
can
be
taken
as
81.003±20.218 with coefficient of variation of 24.96%. This indicates the
existence of some notable variability in carbon stock of soils in the grazing
system.
Figure 12. Soil carbon stock and its carbon dioxide equivalent distribution
with dept at selected site in Dire grazing system of Borena
Zone, Oromia region (DK = Dubuluk; RC = Rare Chebicha;
DM = Dida Medhecho).
As baseline information, mean terrestrial carbon stock and its carbon
dioxide equivalent for the Dire grazing system can be taken as
81.697±20.248 and 303.498±74.312 t ha-1, respectively, with coefficient
of variation of 24.49%. From the foregoing, it can be seen that there
exists spatial variation in terrestrial carbon stock within the same grazing
system. This highlights the need for increasing the intensity of sampling
in future studies to obtain a more representative value for the system.
Comparison of the two sub-systems indicates that the Dire grazing
system is better in its terrestrial carbon stock than the Malbe grazing
system (Figure 13). However, the variability was slightly higher at Dire
than it was at the Malbe grazing system.
If the carbon dioxide sequestered is converted into carbon finance using
the Ethiopian Wildlife Authority rate of $4/tCO2e, the amount of money
generated will be US$ 894.916 and 1213.952 per ha of grazing land,
respectively, for Malbe and Dire grazing systems. This clearly highlights
the importance of carbon sequestration as potential source of income for
the pastoral community in addition to its direct role in improving
productivity of the grazing systems and mitigating climate change by
reducing the CO2 emission from grazing systems.
Figure 13. Mean terrestrial carbon stock and its carbon dioxide equivalent
for Malbe and Dire grazing systems in Borena Zone of Oromia
region.
3.3.3. Terrestrial carbon stock of the Dida Dheda grazing system
3.3.3.1. Overview of the system
This grazing system is located in Liben Woreda of the Guji Zone, Oromia
National regional state. The Woreda is bordered on the south by the Dawa
River, which separates it from the Borena Zone, on the west by Odo
Shakiso, on the northwest by Adolana Wadera, on the north by the
Genale Dorya River, which separates it from the Bale Zone, and on the
east by the Somali Regional state. The altitude of this Woreda ranges
from 1120 to 1600 meters above sea level. According to the 2007 Census
made in the country, the population of the Woreda was 138,813. Both
pastoralism and agro-pastoralism are being practiced in the Woreda.
Some of the farms are even large scale farms that involve mechanization.
The main livestock kept in the area are dominantly cattle mixed with
shoats and to some extent camel.
Two well established sub-grazing systems, Miessa and Siminto, that were
under the participatory rangeland management scheme were selected for
this baseline carbon stock study. At Miessa alone the community
protected 1200 ha as communal Kallo, while no concrete information was
obtained from concerned offices about the size of the Siminto communal
Kallo. These sites are characterized by extensive grazing lands covered
mainly by grasses with scattered acacia and some noxious species. The
specific sampling site was Andereka in Meesa, and Haro Areero in
Siminto. Samples were collected from protected kallos and adjacent
unprotected grazing lands. This is shown in Plate 10 below.
Plate 10. Partial view of the sampling sites at Meesa (upper) and Siminto
(lower) sub-systems at Dida Dheda grazing system. The upper
and bottom left photos indicate the protected kallos at both subsystems, while the adjacent ones indicate the unprotected
grazing lands.
The textural classes of the soils are dominantly sandy loam and sandy
clay loam indicating the relatively large proportion of the sand fraction.
The bulk density values ranged from 0.98 to 1.52 g cm-3 at the soil
surface, and 1.13 to 1.42 g cm-3 at the subsurface layers. Furthermore,
the bulk density of the protected lands was lower than the unprotected
lands at Siminto sub-system. The pH values ranged from 7.21 to 7.78 at
the soil surface, and 6.83 to 7.66 at the subsurface layers. In general, the
pH values in the grazing system were in the range of neutral to
moderately alkaline (Tekalign, 1991). This pH range is suitable for most
plants and indicates that the system has high potential for further
improvement.
3.3.3.2. Results and discussion
At the Dida Dheda grazing system, both vegetation cover and the soil
contributed considerably to the terrestrial carbon stock (Table 11).
Consequently, the vegetation accounted for 34.16% (23.705 t ha -1) and
23.27% (21.174 t ha-1) at protected areas of Mieeso and Siminto,
respectively. On the other hand, nearly 99.99% (49.28 and 61.09 t ha-1)
of the terrestrial carbon stock at unprotected areas of Mieesa and
Siminto, respectively, was stored in the soil system. This clearly shows
the importance of protecting the grazing sites for improving their carbon
sequestration potential and also productivity. The difference in carbon
stock between protected and unprotected lands is largely due to
difference in vegetation cover particularly the scattered trees found in the
system. As can be seen from the data in Table 11, the difference in soil
carbon stock between protected and unprotected lands is low. This has an
important implication if improving the carbon stock in the soil system
through such management practices is envisaged. The implication is that,
in addition to relieving the grazing land from pressure through enclosure,
controlled grazing has to be exercised when livestock are allowed to
graze. Otherwise, nothing will return in to the soil system if intensive
grazing is allowed.
The corresponding carbon dioxide equivalent across the system varied
from a minimum of 180.880 t ha-1 at the unprotected grazing land of
Mieesa to a maximum of 333.911 t ha-1 at the protected grazing land of
Siminto (Table 11). Furthermore, it is important to note that, at both
grazing sub-systems, the minimum carbon stock and its carbon dioxide
equivalent was recorded at the adjacent unprotected grazing lands.
However, this was not reflected in the soil carbon stock at Mieesa. This
might give an indication that the building up of the soil carbon stock
through such management practices might require relatively longer period
than usually anticipated. This in turn implies that the way the protected
grazing lands are grazed after sometime of protection requires caution
not to totally remove the vegetation cover, which is the source of organic
carbon pool in the soil.
Table 11. Terrestrial carbon stock and its carbon dioxide equivalent at
some grazing site in Dida Dheda grazing system, Guji zone of
Oromia region
Carbon stock (t ha-1) in
BGB
Soil
Total
3.95
45.68
69.385
49.28
49.286
Site
CO2e (t ha-1)
AGWV HV
Meesa P
19.75 0.005
254.643
Meeas
0.006
180.880
Up**
Siminto P
17.64 0.004 3.53
69.81
90.984
333.911
Siminto
0.003
61.09
61.093
224.211
Up
Mean±StD
56.465±11.067 67.687±17.585 248.411±64.537
AGWV = above-ground woody vegetation; HV = herbaceous vegetation; BGB = belowground biomass; StD = standard deviation; P* = protected; Up** =
unprotected
Spatial variation in soil carbon stock with soil depth was observed (Figure
14). However, the variation was consistent with depth in the unprotected
grazing lands only. The variation among the sampled sites within the
system, as indicated by the coefficient of variation (19.60%), was
relatively acceptable. The mean soil carbon stock for the system can be
taken as 56.465±11.067 tha-1 with a corresponding carbon dioxide
equivalent of 207.227±40.616 t ha-1.
Figure 14. Soil carbon stock and the corresponding carbon dioxide
equivalent variation with soil depth at selected sites in Dida
Dheda grazing system, Guji zone of Oromia region (MSP =
Meesa protected; MSUP = Meesa unprotected; STP =
Siminto protected; STUP = Siminto unprotected).
There was no information on the total area of the Dida Dheda grazing
system. As a result, it was not possible to calculate the total terrestrial
carbon stock and its carbon dioxide equivalent for the system. Its carbon
stock and equivalent carbon dioxide were, therefore, represented by the
mean values of the two systems, which were 67.687±17.585 and
248.411±64.537 t ha-1, respectively. The monetary value of the carbon
dioxide sequestered, based on the Ethiopian Wildlife Authority rate of
$4/tCO2e, amounts to US$ 993.644 per ha of grazing land.
3.3.4. Terrestrial carbon stock of the Golba Genale grazing system
3.3.4.1. Overview of the system
This grazing system is found in Goro Dola Woreda of Guji zone in Oromia
regional state. It is a new Woreda. This grazing system is covered mainly
by traditionally protected forest and is characterized by undulating
topography. It is dominated by agro-pastoralism with limited pastoralism
in the lowland areas of the system. Cattle are the dominant livestock kept
in the system. Partial view of the nature of forest at Golba Genale grazing
system is illustrated in Plate 11.
Plate 11. Partial view of the sampled forest at Guduba Burure (upper),
active participation of local partners in the study (bottom left),
and nature of some trees at Mucho sampling site in Golba
Genale grazing system.
The soils are highly variable in their textural class. Accordingly, sand to
sandy clay loam textural classes are recorded across the Golba Genale
grazing system. The bulk density of the surface layers ranged from 1.62 g
cm-3 at Guduba Burure to 1.67 g cm-3 at Mucho, whereas at the
subsurface layers it varied between 1.25 g cm-3 at Mucho to 1.68 g cm-3
at Guduba Burure. The pH of the soils, on the other hand, ranged
between 7.02 and 7.35, which fall in the range of neutral to moderately
alkaline, respectively (Tekalign, 1991).
3.3.4.2. Results and discussion
Because the system is dominantly covered by forests of different species,
the contribution of this forest cover to the terrestrial carbon stock of the
system was significant. Therefore, the forest’s carbon stock accounted for
33.8% (43.940 t ha-1) and 28.72% (41.952 t ha-1) at Guduba Burure and
Mucho sub-systems, respectively (Table 12). On the other hand, the soil
system, even under forested environment, proved to be the major carbon
sink in this grazing system. The results further indicate that combined
management of vegetation cover and soil could result in high carbon
sequestration and, thus, play a key role in climate change mitigation. This
can be seen from the high carbon dioxide equivalent sequestered (477.10
to 536.011 t ha-1) in this grazing system.
Table 12. Terrestrial carbon stock and its carbon dioxide equivalent at
Golba Genale grazing system in Guji zone of Oromia region
Carbon stock (t ha-1) in
BGB Soil
Total
7.32
86.06
130.00
Site
CO2e (t ha-1)
AGWV HV
Guduba
36.62
477.10
Burure
Mucho
34.96 0.002 6.99
104.10
146.052
536.011
Mean±StD
95.080±12.756 138.026±11.350 506.556±41.656
AGWV = aboveground woody vegetation; HV = herbaceous vegetation; BGB =
belowground biomass; StD = standard deviation
The depth-wise distribution of the soil carbon stock indicates that the
upper 0-10 cm soil layer contributed the greatest share of the total soil
carbon stock at both grazing sub-systems (Figure 15). This could be
attributed to the relatively high contribution from the forest litter.
Furthermore, the variability of the soil carbon stock within the system was
relatively low with mean value of 95.080±12.756 tha-1 and coefficient of
variation of 13.42%.
Figure 15. Soil carbon stock and its carbon dioxide equivalent distribution
with soil depth at Golba Genale grazing system, Guji Zone of
Oromia region (GB = Guduba Burure; MC = Mucho).
Similar to what has been done for the other systems, the baseline mean
carbon stock and its carbon dioxide equivalent of the Golba Genale
grazing system were taken as the means of the two sub-systems, which
were 138.026±11.350 and 506.556±41.656 t ha-1, respectively.
The monetary value of the carbon dioxide sequestered, using the
Ethiopian Wildlife Authority rate of $4/t CO2e, will be US$ 1908.4 and
2144.044 per hectare of land, respectively, at Guduba Burure and Mucho.
Again, these figures indicate the potential grazing lands in pastoral and
agro-pastoral areas have as sources of huge finance if carbon financing
mechanisms are put in place. The impact of this financial income on
improving the livelihood of the pastoral communities is immense. It is,
therefore, imperative to recognize the potential these lands have to
sequester
significant
amount
of
carbon
within
them
and
device
management scenario that will protect them from degradation and help
them achieve their potential.
Comparison of the two systems indicates that the terrestrial carbon stock
of the Golba Genale system, which is covered by forest, was higher than
that of the Dida Dheda system, which is dominated by annual grasses and
scattered acacia trees and noxious shrubs (Figure 16). Furthermore, the
variability of the terrestrial carbon stock was relatively high at the Dida
Dheda system than it was at the Golba Genale system.
Figure 16. Mean terrestrial carbon stock and its carbon dioxide equivalent
at two grazing systems in Guji Zone, Oromia region (DDH =
Dida Dheda; GG = Golba Genale).
4. CONCLUSIONS
In this study carbon stock was measured in Ethiopian Somali, Afar and
Oromia regions grazing systems as part of improved governance for
climate smart natural resource restoration and enhancement activity of
the PRIME project. The study clearly showed carbon stock differences
within and among clusters, and between protected and unprotected
rangeland systems. This variation is attributed to the observable
differences in management, vegetation cover density, vegetation type,
and soils in the study areas. Those systems with woody perennial
composition had better carbon stock than the other systems which do not
have woody perennials. In all the grazing systems studied, the soil
system was found to be the major carbon sink. Unlike many other forest
based grazing systems, the Hussien Semane sub grazing system in
Harshin grazing system had no undergrowth vegetation, which further
needs investigation on the soil characteristics, grazing system and soil
seed bank.
The baseline carbon stock status indicates that pastoralists, through long
existing customary system, have developed deep understanding of their
grazing
systems
and
have
well
established
rangeland
utilization
mechanisms though it is now being eroded due to internal and external
factors. Revitalization of the customary system and injecting modern
knowledge into it is vital to sustain the rangeland systems and enhance
their environmental and economic contribution to the pastoral community
in particular and the nation at large. The results obtained disproof the
usual belief that pastoral area grazing systems are degraded and have
poor carbon stock and sequestration potential.
The difference in carbon stock between protected and unprotected
rangelands is a clear indication of the contribution of participatory
rangeland management practices and their potential in mitigating climate
change besides improving the productivity of rangelands and livestock.
The current community based natural resources management, particularly
the participatory rangeland management practice, should be strengthened
as these activities are enhancing the carbon stock and sequestration
potential of rangelands.
5. RECOMMENDATIONS
The following recommendations are suggested to fully utilize the potential
of rangelands in climate change mitigation:

The study was conducted during the wet (East cluster) and dry (all
other clusters) seasons. Therefore, results only reflect one season
carbon stock of the respective study areas. Similar studies should be
conducted during different seasons to get the full picture of the
annual carbon stock dynamics of the rangeland systems.

Currently PRIME is using community maps which indicate location of
resources, mobility roots and other important events but not the total
area of the grazing systems that are going to be under participatory
rangeland management scheme. Though rangeland systems covered
hundred and thousands of hectares, it was difficult to obtain their
areal coverage from any sources. The area coverage of the different
grazing systems should be mapped.

The trade-offs between the government formal administrative system
and PRIME rangeland system (following customary system) should be
resolved and all parties should agree on the coverage of rangeland
systems.

These preliminary results should be communicated to decision
makers for guiding policies in pastoral area grazing systems.
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