Journal of Environmental Protection, 2011, 2, 1069-1075
doi:10.4236/jep.2011.28123 Published Online October 2011 (http://www.scirp.org/journal/jep)
Carbon Storage in Agroecosystems: A Case Study
of the Cocoa Based Agroforestry in Ogbese Forest
Reserve, Ekiti State, Nigeria
David Oke, Ayodeji Olatiilu
Department of Forestry and Wood Technology, Federal University of Technology, Akure, Nigeria.
Received June 8th, 2011; revised August 19th, 2011; accepted September 18th, 2011.
ABSTRACT
Large areas of the indigenous tro pical forests in the sou thwestern part of Nigeria a re being converted into agricultural
lands and this has been repo rted to have serious implication s for biodiversity and the environmen t. Cocoa based agro-
forestry is one of the common agricu ltural practices in this region and comparative information on the carbon storage
capacity of the cocoa agroforests is generally lacking. In this study the above-ground carbon storage and partitioning
in a protected primary forest were evaluated and compared with those of the two categories of cocoa agroforests
(sparse and dense) identified in the area. Above-ground biomass accumulation and carbon stock varied significantly
with land use type, with the primary rainforest having the highest values and sparse cocoa agroforests having the low-
est. A reduction in above-ground carbon stock of 89.82% and 71.20% was observed 10 years after conversion of tropi-
cal rainforest to sparse and dense cocoa agroforests respectively.
Keywords: Carbon Sequestration, Cocoa, Agroforestry, Forest Conversion, Global Climate Change
1. Introduction
Carbon dioxide (CO2) is one of the greenhouse gases and
a primary agent of global warming. It constitutes 72% of
the total anthropogenic greenhouse gases, causing be-
tween 9% - 26% of the greenhouse effect [1]. Reference
[2] reported that the amount of carbon dioxide in the
atmosphere has increased from 280 ppm in the pre-
industrial era (1750) to 379 ppm in 2005, and is increas-
ing by 1.5 ppm per year. Dramatic rise of CO2 concen-
tration is attributed largely to human activities. Over the
last 20 years, majority of the emission is attributed to
burning of fossil fuel, while 10% - 30% is attributed to
land use change and deforest at i on [3] .
Article 4 of the United Nations Framework Conven-
tion on Climate Change (UNFCCC) requires preventing
and minimizing climate change by “limiting anthropo-
genic emissions of greenhouse and protecting and en-
hancing greenhouse gas sinks and reservoirs” [4]. Forest
ecosystem plays very important role in the global carbon
cycle. It stores about 80% of all above-ground and 40%
of all below-ground terrestrial organic carbon [3]. How-
ever, the state of tropical forests has continued to dete-
riorate.
Reference [5] reported that the protection of existing
forests, regeneration of degraded forests and raising of
forest plantations have been contributing to enhanced
carbon stock in India. However, the data available on
carbon sequestration i.e. net woody biomass accumula-
tion in trees for long term storage in tropical forests are
extremely limited and incomplete. Thus, the improved
quantification of carbon pools and fluxes in tropical for-
est ecosystems is important for understanding the con-
tribution of these forests to net carbon emissions and
their potential for carbon sequestration [6].
Agroecosystems play a central role in the global car-
bon cycle and contain approximately 12% of the world
terrestrial carbon [7]. From the perspective of climate
change and the global carbon cycle, agroforestry is at-
tractive because the tree component has the capacity to
fix and store carbon from the atmosphere for many years.
The amount of carbon sequestered largely depends on
the agroforestry system put in place, the structure and
function of which are, to a great extent, determined by
environmental and socio-economic factors. Other factors
influencing carbon storage in agroforestry systems in-
clude tree species and system management.

Carbon Storage in Agroecosystems: A Case Study of the Cocoa Based Agroforestry in Ogbese Forest Reserve, 1070 Ekiti State, Nigeria
Cocoa agroforests are a common farming system in
the humid zone of West and Central Africa, in which
forest trees provide shade and other environmental ser-
vices as well as marketable products [8]. Traditionally,
small holder cocoa farmers establish their farms by re-
moving the forest under-storey and thinning the forest
canopy so that Coco a seedlings can grow into produ ctive
trees, as for example in Cameroon [9]. Many authors
[10-14] have described the physiological, environmental
and economic values of shade trees in cocoa growing
systems. They cited benefits such as shade to cocoa, soil
fertility maintenance, biodiversity conservation, protec-
tion against drought, bush fires and insect attacks as well
as additional income through sales of timber species, fuel
wood, and non-wood forest products.
The trees in cocoa agroforests can store carbon in their
shoots and roots, while performing the aforementioned
roles thereby reducing the greenhouse effect. This study
was carried out to assess and compare carbon storage in
cocoa based agroforestry systems and a relatively un-
touched rainforest in Ogbese Forest Reserve, Ekiti State,
Nigeria.
2. Materials and Method
2.1. The Study Area
The study was carried out in Ogbese Forest Reserve in
Ekiti State, (Lat. 7˚31' and 7˚49'N and Lat. 5˚7' and
5˚27'E). The area lies entirely within the pre-Cambrian
Basement Complex rock group which underlies much of
Nigeria. The elevation reaches 600 m above the sea level
and is situated entirely within the upper Ogbese basin.
The area experiences a tropical climate with distinct
wet and dry seasons. Th e rainy season lasts for 9 months
annually between March and November while the dry
season lasts for 3 months between December and Febru-
ary. The annual mean total rainfall is 1367 mm; the av-
erage number of the rainy days is 112 per annum [15].
Temperature is almost uniform throughout the year
with very little deviation from the mean annual of 27˚C.
The mean annual relative humidity varies between 50%
and 95% and is high est in the rainy season months.
2.2. Sampling
Ten-year-old cocoa farms established in, and around
Ogbese Forest Reserve, Ekiti State were visited to select
appropriate sites for this study. Based on the number of
shade trees (non cocoa trees) per unit area, the farms
were classified into dense and sparse mixtures. Four
farms under each category were selected for detailed
biomass measurement. Sample plots were also demar-
cated within the natural forest whose canopy had not
been disturbed by th e activity of a coco a farmer or wher e
there is little or no evidence of timber extraction. One
plot (25 m × 25 m in size) was located in each of the
selected cocoa farms and four at random locations within
the natural forest.
2.3. Biomass Estimation
All cocoa trees in each plot were measured for stem di-
ameter distribution. Two mean cocoa trees with dbh
nearest to the mean dbh were located in each of the plots
within cocoa farms and selected for destructive sampling
after their heights, diameters at the base, at the middle
and at the top have been measured and recorded. The
biomass measurements were based on the biomass sub-
sampling method outlined by [16]. The two mean cocoa
trees were felled at the ground level. Each felled tree was
sorted into the three main components; bole, branches
and foliage and each component was cut into small
pieces for easy weight measurement. Samples were taken
to the laboratory for dry weight determination. As rec-
ommended by [16], stem material removed in saw cuts
were also considered as 0.5% of the stem biomass. Vo-
lumes of the two (2) mean cocoa trees in each sample
plot were calculated using the Newton’s formula by [17].
Diameter and height measurements of all the non co-
coa trees in each plot were also taken and their volumes
calculated using the Newton’s formula by [17]. However,
due to the variety and size of non cocoa tree species en-
countered and the difficulty in getting the cocoa farmers
to allow felling of such shade trees because of the fear of
massive destruction of non target cocoa trees that could
accompany such an exercise, the above ground biomass
of non cocoa trees in the plots was estimated indirectly
from the volume data using the formula:
Aboveground biomass = VOB × WD × BEF
where:
WD = volume-wei g ht ed average wood dens it y
BEF = biomass expansion factor (ratio of aboveground
oven-dry biomass of trees to the oven-dry biomass of
inventoried volume). WD was estimated as described by
[18].
The wood density values (Table 1) were obtained
from [18]. The biomasses were added for each plot and
expanded to biomass in tonnes per hectare.
2.4. Carbon Estimation
The carbon concentration of different tree parts is rarely
measured directly, but generally assumed to be 50% of
dry weight [19]. Hence in this study, the aboveground
carbon stock was calculated by assuming that the carbon
content is 50% of the total aboveground biomass [5,
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Carbon Storage in Agroecosystems: A Case Study of the Cocoa Based Agroforestry in Ogbese Forest Reserve,
Ekiti State, Nigeria
1071
20-24].
2.5. Data Analysis
Correlation analysis was carried ou t to examine relation-
ships between some paired growth parameters. Carbon
storage values estimated for sparse mixtures, dense mix-
tures and the natural forest were compared using one
way Analysis of Variance (ANOVA). The three (3)
stands formed the treatments while the four (4) plots
sampled in each of the stands formed the replicates. The
test was conducted for significant difference in the car-
bon stock for the three different stands. Mean separation
was carried out with Fisher’s Least Significant Differ-
ence (LSD) where significant differences occur (P <
0.05).
3. Results
3.1 Distribution of Cocoa and Shade Tree
Species
Seventy six shade trees were encountered in the 1 ha of
dense cocoa agroforests and these were made up of 9
different species in 5 families while 40 shade trees en-
countered in sparse cocoa agroforests and these were
distributed in 5 species and 4 families. In the one hectare
of natural forest surveyed, 166 trees were encountered
and these were distributed in 15 species and 7 families
(Table 2). Ficus mucuso was found to be the most fre-
quently occurring species with 41, 22 and 18 trees in the
natural forest, dense cocoa agroforest and sparse cocoa
agroforest respectively. This was followed by Antiaris
africana occurring 25, 14 and 10 times respectively. The
highest number of trees (336) were encountered in the
sparse cocoa agroforests and these were made up of 296
cocoa trees and 40 shade trees (Table 3). In the dense
mixture 308 trees were recorded made up of 232 cocoa
and 76 shade trees. There were 166 trees in the natural
forest which contained no cocoa tree.
The summary of the cocoa tree growth data presented
in Table 4 for Sparse and Dense Cocoa Agroforests
shows that Mean Dbh and Mean Height respectively
Table 1. Scientific names, family and wood density (as obtained from [18]) of the non cocoa tree species encountered in the
study area.
Species Family Wood Density (t/m3)
Afzelia Africana Kuntze Leguminoseae 0.63
Triplochiton scleroxylon Schumann Sterculiaceae 0.32
Ficus mucuso Welw ex. Ficalho Moraceae 0.39
Pterygota macrocarpa K. Schum Sterculiaceae 0.52
Terminalia superb Engl. & Diels Combretaceae 0.45
Antiaris Africana Engl. Moraceae 0.37
Sterculia oblonga Mast. Sterculiaceae 0.61
Alstonia boonei De Wild Apocynaceae 0.33
Entandrophragma utile Sprague Meliaceae 0.53
Celtis zenkeri Engl Ulmaceae 0.59
Daniella oliveri Rolfe Caesalpiniaceae 0.40
Terminalia ivorensis A. Chev Combretaceae 0.45
Holoptelia grandis Hutch (Mildbr) Ulmaceae 0.59
Nesogordonia papaverifera A.Chev. Sterculiaceae 0.65
Khaya ivorensis A.Chev. Meliaceae 0.44
Pycnanthus angolensis Welw Myristicaceae 0.40
Daniella ogea Harms Leguminoseae 0.40
Gossweilerodendron balsamiferum Harms Leguminoseae 0.40

Carbon Storage in Agroecosystems: A Case Study of the Cocoa Based Agroforestry in Ogbese Forest Reserve, 1072 Ekiti State, Nigeria
Table 2. Diversity of non cocoa/shade tree species in 1 ha of sampled ecosystems in Ogbese Forest Reserve.
Natural Forest Dense Cocoa Agroforest Sparse Cocoa Agroforest
Species Freq. Species Freq. Freq.
Afzelia africana 10 Triplochiton scleroxylon 9 Ficus mucuso 18
Triplochiton scleroxylon 12 Ficus mucuso 22 Antiaris africana 10
Ficus mucuso 41 Antiaris Africana 14 Sterculia oblonga 4
Pterygota macrocarpa 11 Pterygota macrocarpa 3 Terminalia ivorensis 6
Terminalia superba 13 Entandrophragma utile 9 Alstonia boonei 2
Antiaris africana 25 Afzelia Africana 4
Sterculia oblonga 10 Daniella oliveri 5
Alstonia boonei 7 Sterculia oblonga 7
Entandrophragma utile 12 Terminalia ivorensis 3
Celtis zenkeri 3
Daniella oliveri 3
Terminalia ivorensis 6
Holoptelia grandis 4
Nesogordonia papaverifera 2
Khaya ivorensis 7
Total 166 Total 76 Total 40
Table 3. Distribution of cocoa and non-cocoa trees in 1 ha of sampled ecosystems in Ogbese Forest Reserve.
Stand Type No of Cocoa Trees/ha No of Shade Trees/ha Total no of trees/ha
Sparse Cocoa Agroforest 296 40 336
Dense Cocoa Agroforest 232 76 308
Natural Forest - 166 166
Table 4. Distribution of aboveground biomass in the c ocoa trees of ten-year-old co c o a agr oforests in Ogbese Forest Reserve.
Stand Type Tree Components Biomass (t/ha) Proportion (%) Carbon (t/ha) Proportion (%)
Sparse Cocoa Agroforest Stem 5.40 83.98 2.70 83.85
Branches 0.81 12.60 0.41 12.73
Foliage 0.22 3.42 0.11 3.42
Total Aboveground Biomass6.43 100.00 3.22 100.00
Dense Cocoa Agroforest Stem 4.80 87.11 2.40 86.96
Branches 0.58 10.53 0.29 10.51
Foliage 0.13 2.40 0.07 2.54
Total Aboveground Biomass5.51 100.00 2.76 100.00
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Carbon Storage in Agroecosystems: A Case Study of the Cocoa Based Agroforestry in Ogbese Forest Reserve,
Ekiti State, Nigeria
1073
were both higher in Dense Cocoa Agroforest (11.70 cm
and 6.79 m) than in the sparse mixture (11.30 cm and
6.66 m), other parameters i.e. Basal area/ha and Volume/
ha were also higher in the Dense stand th an in the Sparse
mixtures. The Basal area/ha was 2.20 m2 and 2.49 m2
while volume/ha was 10.46 m3 and 12.47 m3 in the
Sparse and Dense Cocoa Agroforests resp ectively. Simi-
larly, the shade trees in Dense Cocoa Agroforests were
higher in all the growth parameters than those in the
Sparse stand as many large trees had been removed from
the Sparse stand while these trees were still providing
much shade in the Dense Cocoa Agroforest. Mean Dbh
and Mean Height of shade trees were 43.60 cm and
21.82 m in the Dense stand compared to 38.30 cm and
21.15 respectively in the Sparse stand. Basal area and
volume of shade trees per ha were 14.92 m2 and 192.65
m3 respectively in the dense stand while 4.46 m2 and
50.80 m3 were recorded for the sparse.
3.2. Aboveground Biomass Accumulation and
Partitioning
The partitioning of biomass in the cocoa trees is pre-
sented in Table 5. A total abo ve ground biomass of 6.43
t/ha was obtained for cocoa trees in the sparse cocoa
agroforest. Stem biomass accounted for an average of
83.98% (5.40 t/ha) while branch and foliage biomasses
accounted for an average of 12.60% (0.81 t/ha) and
3.42% (0.22 t/ha) respectively. In the Dense Cocoa
Agroforests, the total above ground biomass of cocoa
trees was 5.51 t/ha. Stem biomass was found to be
87.11% (4.80 t/ha) while branch and foliage biomasses
were 10.53% (0.58 t/ha) and 2.40% (0.13 t/ha) respec-
tively. The highest total above ground biomass (333.34
t/ha) was observed in the natural forest while the least
was in the sparse cocoa agroforest (Table 6). Only
5.73% of the 96.01 t/ha of biomass observed in the dense
cocoa agroforests was accounted for by the cocoa trees.
The cocoa trees also accounted for 18.97% of the above-
ground biomass in the sparse cocoa agroforests.
3.3 Carbon Storage in the Cocoa Agroforests
and the Natural Forest
Figure 1 shows the aboveground carbon storage in the
three types of ecosystems considered. Statistical analysis
showed that Carbon storage/ha varied significantly
among Sparse Cocoa Agroforest, Dense Cocoa Agrofor-
est and the Natural Forest. The highest value of 184.99
t/ha was obtained for the natural forest while the least
was in the sparse cocoa agrofore st.
4. Discussion
Numerically, there were more trees in the sparse cocoa
agroforests than in the other two ecosystems but a high
proportion of these were cocoa trees which were smaller
in size compared to the non cocoa trees. The summary of
the Cocoa tree growth data shows that the Dense Cocoa
Agroforest had higher Mean Dbh and Mean Height than
the Sparse Cocoa Agroforest and there were more natural
or shade trees in the Dense mixtures than in the sparse
mixtures. The lower growth parameters (Mean Dbh,
Mean Height, Mean Basal Area and Mean Volume) in
the sparse mixture may be attributed to the closer spacing
of the cocoa trees as there were more cocoa trees per
hectare than in the Dense mixtures. The minimum and
maximum Dbh recorded for cocoa trees in the Dense
Cocoa agroforest were also higher than those of the Sparse.
Table 5. Growth of cocoa and non cocoa trees in the cocoa agroforests and natural forest of Ogbese Forest Reserve.
Sparse Cocoa Agroforest De nse Cocoa Agroforest Natural Forest
Cocoa Non-Cocoa Cocoa Non-Cocoa Non-Cocoa
MDbh (cm) 11.30 ± 0.00 38.30 ± 0.12 11.70 ± 0.00 43.60 ± 0.01 49.43 ± 0.08
MHt (m) 6.66 ± 0.51 21.15 ± 1.21 6.79 ± 0.12 21.82 ± 0.86 24.76 ± 1.87
No./ha 296.00 ± 1.29 40.00 ± 0.58 232.00 ± 0.58 96.00 ± 0.82 188.00 ± 1.71
Vol/ha (m3) 10.46 ± 0.02 50.80 ± 0.49 12.47 ± 0.00 192.65 ± 0.24 673.88 ± 1.04
Ba/ha (m2) 2.20 ± 0.00 4.46 ± 0.08 2.49 ± 0.00 14.92 ± 0.01 39.96 ± 0.06
Table 6. Aboveground biomass (t/ha) the 10-year-old c ocoa agrofore sts and natur al fore st of Ogbese F ore st Reser ve.
Sparse Cocoa Agroforest Dense Cocoa Agroforest Non-Cocoa
Cocoa 6.44 5.51 0
Shade tree 27.50 90.50 333.34
Total 33.94 96.01 333.34

Carbon Storage in Agroecosystems: A Case Study of the Cocoa Based Agroforestry in Ogbese Forest Reserve, 1074 Ekiti State, Nigeria
Figure 1. Biomass and carbon storage/ha in the study area.
Growth parameters such as MDbh, MHt, Volume and
Basal area of non cocoa trees were all higher in the Dense
Cocoa Agroforest than in the Sparse mixture. This may
be attributed to the removal of many large shade trees in
the Sparse mixture to open the canopy for the establish-
ment of Cocoa plantation.
The mean Aboveground Biomass (AGB) for Cocoa
trees in the Dense Cocoa Agroforest was higher than that
of the Sparse mixture. This is in agreement with the re-
ports of [25] on the effect of shade tree in an 8-year-old
cocoa Agroforestry system in which they concluded that
Cocoa Biomass was higher under shade. The proportion
of AGB concentrated in the stem was also found to be
higher in Dense Cocoa Agroforest than in the Sparse.
This is due to the fact that more AGB were in branches
and foliag e of Sp arse Coco a Agr ofo re st th an in the Den se
Cocoa Agroforest. Cocoa trees in the Dense Cocoa
Agroforests were found to have more stem Bio- masses
and less branch and foliage Biomasses than those in the
Sparse Cocoa Agroforest.
The aboveground Biomass of shade trees in the Dense
mixture was higher than in the Sparse due to the number
and size of the trees found in the stands. Total AGB/ha
was highest in the natural forest followed by the Dense
and the Sparse mixtures in that order for the same reason.
TAGB was more than three times higher in the natural
forest than in the Dense Cocoa agroforest. Reference [26]
reported that the values for natural forest could be about
3 - 4 times higher. The total aboveground Biomass ob-
tained in the natural forest is comparable to 444.70 t/ha
obtained by [ 2 7] in Indonesia.
The carbon storage va lue of 57.5 5 t/h a observ ed for ten
year old Dense Cocoa Agroforest in this study was less
than that obtained in Mango Agroforestry system (121.1
t/ha) in Indonesia [28] and higher than that of
five-year-old Cocoa-gliricidia (38.86 t/ha) [29].
In the natural forest, the large trees contributed more
than 45% to the total AGB. The greater contribution of
large trees to AGB in natural forest is in agreement with
the findings of previous workers [30-32] who reported up
to 50% contribution to AGB by large trees (of Dbh > 0.7
m). A higher proportion of AGB in the large trees in the
natural forest indicates that such trees play important role
in Carbon storage; no twithstand ing, small trees (of Dbh <
0.6 m) enhance future Carbon storage as they are high in
Carbon storage potential.
5. Conclusions
The study shows that AGB of Cocoa increases with in-
crease in density of shade trees. It was also discovered
that growth characteristics of Cocoa are higher under
shade.
It has been shown clearly by the result of this study
that Cocoa Agroforests store substantial Carbon as seen
in the Dense Cocoa Agroforest. From the perspective of
climate change, Cocoa Agroforests are attractive; not
only that the Cocoa component stores Carbon in addition
to the natural trees but also that the system potentially
slows down deforestation by reducing the need to com-
pletely clear forestland for agriculture. This will be more
acceptable to rural farmers than complete afforestation.
Therefore Cocoa Agroforest is recommended as one of
the options in combating climate change.
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