Biomass and Soil Carbon Stocks Assessment
of Agroforestry Systems and Adjacent Cultivated Land, in Cheha Wereda, Gurage Zone, Ethiopia
Ethiopian Environment and Forest Research Institute, Ethiopia
Submission: July 10, 2019; Published: July 25, 2019
*Corresponding author: Mihert Semere, Ethiopian Environment and Forest Research Institute; P.O.Box 24536 Code 1000, Addis Ababa Ethiopia
How to cite this article: Mihert Semere. Biomass and Soil Carbon Stocks Assessment of Agroforestry Systems and Adjacent Cultivated Land, in Cheha Wereda, Gurage Zone, Ethiopia. Int J Environ Sci Nat Res. 2019; 20(4): 556043. DOI:10.19080/IJESNR.2019.20.556043
The present study examined biomass and soil carbon stock potentials of different agroforestry system (AFS) [home garden and woodlot] and cultivated land in Cheha Werda, Gurage zone, Ethiopia. The sites and land use types were selected based on dominance and accessibility through reconnaissance survey prior to sampling. A total of 60 sample plots and 20m x 20m for each land use type were randomly selected. Above ground biomass (AGB) and below ground biomass (BGB) were calculated by adopting allometric equations. A total of 120 Soil samples from two depths were also collected to determine soil organic carbon (SOC), pH, texture and bulk density (120 samples). The results showed that the total ecosystem carbon stocks in home garden and woodlot AFS were 100.4 and 72.9Mg C ha-1 respectively. The highest SOC stock was recorded in home garden agroforestry system. The study also revealed that AFS enhance carbon stocks accumulation both in the biomass and soil besides the socioeconomic benefits over cultivated land. Hence, AFS can be taken as potential climate change mitigation strategy in central highlands of Ethiopia.
Keywords: Biomass; Carbon stocks; Agroforestry
Abbrevations: AFS: Agroforestry System; AGB: Aboveground Biomass; AGBC: Above Ground Biomass Carbon; BD: Bulk density; BGB: Below Ground Biomass; BGBC: Below Ground Biomass Carbon; DBH: Diameter at Breast Height; H: Height; IPCC: International Panel for Climate Change; SOC: Soil Organic Carbon; TBC: Total Biomass Carbon
Agroforestry system comprises one or more agricultural and forestry systems with beneficial effects by creating biological, socioeconomic and ecological interaction among trees or shrubs (woody perennials) with crops and/or animals . The major components of agro forestry systems are trees, shrubs (woody perennials, including bamboos) and animals. These are intentionally retained or planted on the farmland to provide multiple products as a source of income generation and household consumption and other ecosystem services.
Forest ecosystem in particular agroforestry systems play a significant role in global climate change mitigation strategy, as the source of income and ecological benefits. Though several efforts have been made to reduce carbon dioxide emission through forestry sector like afforestation and enhancing agroforestry systems most of them are unaccounted locally to show the contribution of the systems. Gurage zone, Cheha Wereda was selected since it incorporates diversified Agroforestry systems and cultivated lands.
This study mainly aimed in assessing of biomass and soil carbon stocks of AFS and adjacent cultivated land in Cheha District, Gurage Zone and Central Highland of Ethiopia. The study explicitly intended to estimate and compare above and belowground biomass carbon stocks and SOC Stocks of different land us types.
The study was conducted in Cheha district, located in Gurage Zone of Southern Nations, Nationalities and Peoples Regional State (SNNPRS), Ethiopia. The geographical location of the Study area is between 8° 00’ 18” and 8° 15’ 28” N and 37° 35’ 46” and 38° 03’ 59” E and average elevation ranges from 1950-1970 meters above sea level (Figure 1). Based on information obtained from the Cheha Wereda agriculture and rural Development Office, the area is characterized by bimodal rainfall Pattern ‘Kiremt’, is the
The mean annual rainfall obtained from the monthly
data on the bases of ten years of records at the neighboring
meteorological station (Imdibir, Gubre and Wolkite) is 1268 mm.
The mean monthly maximum and minimum temperatures are
25°C and 11°C respectively and dominant soil type of the study
site is Vertisol which covers 82.4 % of the study area.
A preliminary reconnaissance survey was conducted in
identify the study area. Key informants i.e. development agents,
elders and district’s natural resource experts were consulted to
identify dominant agroforestry systems. Accordingly, Kebeles
with home garden, woodlot agroforestry system and cultivated
land were identified. Among the list of identified kebeles two
kebeles, Yefekterk endebera and yefekterk wedro kebeles
were randomly selected as site replications. A total of 60 farms
consisting of 20 farms for each land use were randomly selected.
The description of vegetation and soil characteristic of
agroforestry system practiced in the study area is given in Table
1 & 2.
A plot size of 20m x 20m was randomly laid down in each
sampled farm to inventory woody species in both the studied
land use systems . All woody species including fruit trees and
non- fruit trees with DBH ≥2.5cm diameter and height ≥1.5m
was measured and recorded .
For coffee plants, stem diameter at stump height (at 40cm)
was measured. Stem diameter measurements (d40) were taken
in two perpendicular directions and the average value taken.
For enset plants stem diameter at stump height (at 10cm) was
measured. In the case of multi-stemmed coffee plants, fruit trees
and non-fruit, all steam in single plant was measured and the
equivalent diameter of the plant calculated as the square root
of the sum of diameters of all stems per plant (Snowdon et al.
Soil samples were collected from the same plots we used for
woody species inventory (20m x 20m) used for woody species
inventory. In this study the soil sample were collected in two
depths (0-20cm and 20-40cm) from three sub plots (two at
the corner and one at the centre) using soil auger and made a
composite sample, for determination of sub plots lottery method
were used. A total of 120 composite samples from the three
subplots were taken to laboratory to determine SOC, pH and soil
texture. Soil samples for bulk density analysis were collected
separately from sample plot (20m x 20m) and1m x 1m subplot
using core sampler size of 5cm diameter consecutively from
0-40cm. A 5cm diameter core sampler was used to take samples
for bulk density and four cores were taken for each depth.
The soil samples for SOC were air dried and sieved with
2 mm sieve for making them ready for further analysis. The
samples were oven dried at 105 °C for 48 hours and weighed
then Walkley and Black method was used for further analysis of
the required parameters .
Above ground biomass carbon stock for each plot (Mg C ha−1)
was estimated as the product of dry matter biomass and carbon
For woody species (Trees) including fruit trees incorporated
within home garden agroforestry, AGB was estimated using
allometric equation developed by Kuyah et al. . We used 48%
for carbon stock conversion.
Where ABG; is the aboveground biomass (kg dry matter/
plant), d = Breast height diameter (cm)
Below ground biomass estimated (BGB) using global average
value of 26% of aboveground biomass (Cairns et al. 1997). We
used 49% for carbon stock conversion .
Where: AGB coffee is aboveground biomass for coffee, d40 =
Stem diameter (cm) of the coffee plant at 40 cm height
AGB and BGB of enset were computed with allometric
equation developed by Negash et al. (2013). 47% was used for
carbon stock conversion.
Where AGB enset is aboveground biomass for enset, d10 is
the basal diameter (cm) of the enset at 10cm height and h is total
height (m), BGB enset is belowground biomass for enset.
For above ground biomass estimation of Eucalyptus viminalis
allometric equation developed by Zerfu H (2002) was adopted.
Since Eucalyptus viminalis has similar vegetation characteristics
with Eucalyptus camaldulness
Below ground biomass estimated using global average value
of 26% of aboveground biomass (Cairns et al., 1997). 50%
(default values) was used for carbon stock conversion.
Where: TAGBC= Total Above ground biomass carbon, Mg C ha-1,
TBGBC= Total below ground biomass carbon, Mg C ha-1 and TBC=
Total biomass carbon
BD and soil organic carbon
SOC stock (Mg C ha-1) was calculated by multiplying the
concentrations (%) of soil carbon, the Bulk density (g cm-3) and
depth of the sampled soil .
Where, SOC = Soil Organic Carbon (Mg C ha-1), BD = Bulk
Density (g cm-3), Depth of the soil sample (cm) and % C =
Microsoft excel version 2010 was used to record, calculate
and organize data. IBM SPSS version 20 software was used for
statistical analysis. One-way Analysis of Variance (ANOVA) was
performed to examine the variations in biomass and soil carbon
stock among the agroforestry system and cultivated land. Post
hoc test was used to evaluate the mean differences across the
studied systems, followed by Tukey test to compare statistical
mean differences among the systems. One-way ANOVA shows
presence of significant differences among mean values of
agroforestry systems and cultivated land in both biomass carbon
and soil organic carbon stocks.
The mean total biomass carbon stocks (Above and below
ground) of home garden and woodlot agroforestry system is
estimated between 2-6Mg ha-1 and 1.9-4.74Mg C ha-1 respectively.
Woodlot agroforestry system was lower by 22% compared
to home garden agroforestry system in TBC. Mean above and
below ground biomass carbon stocks showed similar leaning in
their biomass carbon stock. The contribution of above ground
biomass carbon stock for total biomass carbon stock in home
garden and woodlot agroforestry systems is averaged at 69%.
Total biomass carbon was highest in home garden as compared
to woodlot and it showed difference between the two studied
agroforestry systems but the difference was not significant at
5% level of significance. Mean biomass carbon stock of home
garden and woodlot agroforestry system was estimated to be
(6.092±2.3Mg C ha−1) and (4.74±6.3Mg C ha−1) respectively (See
In home garden agroforestry system enset and coffee plus
tress accounts 83% and 17% respectively for the total biomass in
the system. This study assumes the difference in carbon between
the two studied agroforestry systems was not significant at 5%
level of significant (Figure 2).
BGBC of the two studied agroforestry systems ranged from
1-4Mg C ha−1. Home garden AFS has significantly higher BGBC
than woodlot AFS (2.03 and 1.9Mgha−1) respectively (See table
3). The contribution of BGBC for the total biomass carbon stock
was 33% and 40% for home garden and woodlot agroforestry
The mean total SOC (0-40cm) of studied land uses was
estimated to be 94.2Mg C ha-1, 73Mg C ha-1 and 68Mg C ha-1 for
home garden, cultivated land and woodlot respectively. The SOC (0-20cm) in home garden agroforestry system was higher by
28% and 23% than woodlot and cultivated land respectively. The
contribution of the upper soil layer (0-20cm) to total SOC stocks
was highest for all AFS home garden agroforestry followed
by cultivated land and woodlot agroforestry than the lower
layer (20-40cm). Conversion of home garden agroforestry and
woodlot to cultivated land would decrease SOC stock by 23%
and increases by 7% respectively.
The total SOC stocks significantly differed between home
garden and the other two studied systems. The SOC stock was
the highest in-home garden and the least in woodlot (See Table
Amongst the studied land uses the highest mean ecosystem
carbon stock was recorded for home garden agroforestry system
(100.38Mg C ha-1) and the least was for woodlot agroforestry
(72.9Mg C ha-1) (See Table 5).
The mean total biomass carbon stock of home garden
agroforestry system accounted in this study was comparable with
the findings in the same agroforestry system in Gununo Watershe
Wolayitta Zone, Ethiopia . Home garden agroforestry system
total biomass carbon in this study was substantially higher
than the parkland agroforestry system in Gununo Watershed,
Wolayitta Zone, Ethiopia  and lower than the studies in enset
and enset coffee agroforestry system in Southern escarpment of
Ethiopia  and in tropical dry deciduous forests (14.7 -43.2Mg
ha-1)  and in Western Kenya (36.9 - 115.9) .
The present study revealed that total biomass carbon
stocks were highest in-home garden as compared to woodlot.
This could be due to lower diameter trees documented in the
earlier system than the later one . Besides, home garden
agroforestry system includes diversified species such as fruit
trees, coffee and enset which could contribute a lot in carbon
storage. Similar studies have also shown that the differences in
biomass carbon stocks depend on several factors such as stand
age, stand structure, diversity and composition and management
Soil organic carbon is a significant carbon pool because it
has the longest dwelling time of carbon among organic carbon
pools (Lugo & Brown, 1993). The mean soil organic carbon
stocks for the 0 –40 cm soil depth within the ranges of African
savannahs and woodland 30-140Mg C ha-1 . SOC in our study
was considerably high as compared to results estimated to be
43Mg C ha−1 for semi-arid Acacia etabica woodland in southern
In this study higher SOC was recorded than the study made
in home garden and woodlot agroforestry in Gununo Watershed,
Wolayita Zone, Ethiopia which accounted 61.6Mg ha−1 and
48.6Mg ha−1 respectively for home garden and woodlot
agroforestry (Batiji et al., 2012). The SOC in this study was lower
than the finding in the south eastern rift valley escarpment of
Ethiopia . Soil physical structure, species composition and
litter quality could be the factors for the variation of SOC among
the systems .
In line with the study management systems determine SOC
of different land use system. Organic matter input and aeration
alters SOC potential since they are the main driver of SOC
stock. The results in this study support this claim, home garden
agroforestry with high litter input as mulching management
system could be the main driver for high SOC than single species
woodlot agroforestry with no additional organic carbon. Low
tillage considered as a measure to sequester carbon . In
the present study low SOC stock recorded in cultivated land
comparing with home garden agroforestry, this could be related
to high tillage management system in cultivated land [16-20].
The present study revealed that more carbon is accumulated
in soil than biomass. Accumulation of fine roots and litter
decomposition could be the factors for SOC and biomass carbon
stock density variation. Land use history and management
systems could also be additional factors (Nair et al. 2009). In this
study, high ecosystem carbon stock was recorded in agroforestry
system than that of cultivated land. This implies the system have
a significant carbon sequestration potential which could help as
climate change mitigation option in the study area [21-25].
The study indicates AFS have high carbon stock potential
compared to cultivated land use systems. Higher carbon stock in both biomass and SOC was observed in home garden
agroforestry system. This study attributes higher biomass
carbon stock in home garden agroforestry than woodlot but
the difference was not significant. The contributions of SOC
stocks for total ecosystem carbon were higher in both studied
agroforestry systems than biomass carbon stock. In a conclusion
this study showed that land use conversion has a significant
effect in biomass and SOC stock potential. Overall this study
will add up information about carbon stock potential of AFP
in central highlands of Ethiopia. It also proves AFS has great
potential SOC storage, emission reduction and carbon financing
scheme as climate change mitigation strategies. Therefore, the
current recognition for agroforestry as climate change mitigation
strategies is strengthened by this study. Therefore, Climate
change mitigation (carbon emission reduction) strategies such
as REDD + should give a great recognition for agroforestry since
it has remarkable potential on contribution for climate change
We acknowledge Ethiopia Environment and Forest Research
Centre (EEFRC), Ethiopian Environment and Forest Research
Institute (EEFRI) for granting me scholarship for pursuing the
study and research fund for this paperwork. The first author
also acknowledges Hawassa University, Wondo Genet College
of Forestry and Natural Resources for the methodological and
Hailu Z (2002) Ecological impact evaluation of Eucalyptus plantations in comparison with agricultural and grazing land-use types in the Highlands of Ethiopia. Vienna University of Agricultural Sciences, Vienna.
IPCC (2002) Third Assessment Report of the IPCC. Cambridge University Press, Cambridge, UK.
MacDicken KG (1997) A guide to monitoring carbon emissions from deforestation and degradation in developing countries: An examination of issues facing the incorporation of REDD into market-based climate policies. Resource for Future, Washington, DC.
World Agroforestry Centre (ICRAF) (2006) Agroforestry for improved livelihoods and Natural resources conservation. An Agroforestry Policy Brief.