Journal of Geoscience and Environment Protection, 2014, 2, 157-166
Published Online April 2014 in SciRes. http://www.scirp.org/journal/gep
http://dx.doi.org/10.4236/gep.2014.22022
How to cite this paper: Eneji, I. S. et al. (2014). Sequestration and Carbon Storage Potential of Tropical Forest Reserve and
Tree Species Located Within Benue State of Nigeria. Journal of Geoscience and Environment Protection, 2, 157-166.
http://dx.doi.org/10.4236/gep.2014.22022
Sequestration and Carbon Storage Potential
of Tropical Forest Reserve and Tree Species
Located within Benue State of Nigeria
Ishaq S. Eneji1*, Ofoegbu Obinna1, Emmanuel T. Azua2
1Department of Chemistry College of Science, Federal University of Agriculture, Makurdi, Benue State, Nigeria
2Department of Biological Sciences, College of Science, Federal University of Agriculture, Makurdi, Benue State,
Nigeria
Received Dec emb er 2013
Abstract
Carbon sequestration potential of tree species within forest reserves and other sites in Makurdi
Benue state of Nigeria was investigated using non-destructive Walkley-Black technique. The result
indicates that P. americana has the highest CO2 seq uestr ation potential (125,916.7 kg), while T.
grandis (10.4 kg) and D. regia (26.1 kg) were the least. The study also shows that trees (T. gran dis ,
S. actinophylla and P. ameri can a) with thick vegetation, broad and clustered leaves were found to
be better CO2 sequesters. The relationship between the tree height and amount of CO2 sequestered
gave a regression equation of y = 67898x + 9509 with R2 = 0.266, indicating insignificant varia-
tions existing between tree height and CO2 sequestration at P > 0.05. Variations however existed
between tree dominance and CO2 sequestration among trees investigated. This finding strategi-
cally positions Benue tropical forest in line for carbon credit financing while substantiating the
importance of preserving our indigenous forest and tree species.
Keywords
Benue; Carbon Credit; Tropical Forest; B io-Diversity; Sequestration Potential; B io-Sink
1. Introduction
The importance of forests in extenuating climate change has led many countries to study the carbon budgets and
carbon sequestration of their forests resource. The total global potential for afforestation and reforestation activi-
ties for the period 1995-2050 is estimated to be an average of 1.35Pg C per year, of which 70% possibly will
occur in the tropics (IPCC, 2001).
Nigeria had sixty (60) million hectares of forest as area as at 1897 and it is established that this has declined
during the 1990s at an estimated annual rate of 2.6% or more (≤398,000 hectares/year) (Oguntala, 1995; FAO,
2005). Observed causative agents were, agricultural expansion, encroachment, over-harvesting, bush burning,
illegal harvesting and de-reservations. The Federal Department of Forestry postulated that the annual diminution

I. S. Eneji et al.
158
rate may be as high as 3.5%, noting that the forest estate of Nigeria is being highly depleted with the Sahara
Desert encroaching southward at a rate of about one kilometer per year. This phenomenon appearing very docile
poses great natural risk and creates a disaster laden picture for the country, this makes mitigation and related
containment activities very imperative.
Plants’ propagative and vegetative mechanisms are known to contribute to the control of the experienced and
increasing carbon dioxide emission in the environment. The utilization of available atmospheric CO2 in photo-
synthetic process provides a natural sink for the excess carbon dioxide generated by anthropogenic activities. It
is known that global emission of carbon dioxide has increased by 18% reaching its first peak level after 1750.
An up surge level increase per year of 1.5 ppb in 1990-2000, 2 ppb in 2001-2009 and 2.3 ppb in 2009-2010 the
highest in recent decades (Chavan and Rasal, 2012). Food and Agricultural Organization (FAO) report estimates
that in Africa, deforestation accounts for nearly 70% of total emissions (FAO, 2005). Clearing tropical forests
also destroy globally important carbon sinks that are currently sequestering CO2 from the atmosphere which are
critical to future climate stabil ization (Stephens et al., 2007).
Effective sequestration which is the net exclusion of carbon dioxide from the atmosphere and entrapment
within long termed natural sinks is achieved by the presence and activities of plant species with life spans of not
less than ten (10) years (SSSA, 2001). With this, estimates of carbon stocks and stock changes in tree biomass
are necessary. Nigeria lack articulated data generation and banking in this area, hence stands to lose her natural
carbon sinks. Above-ground biomass, below-ground biomass, dead wood, litter, and soil organic matter are the
major carbon pools in any flora and fauna (Chavan and Rasal, 2012). Soil organic carbon is a large and active
pool, containing roughly twice as much carbon as the atmosphere and 2.5 times as much as the biota and the amount
of carbon sequestered at a site reflects the long-term balance between influx and efflux of carbon (SSSA, 2001).
Benue state (7˚43'50"N 8˚32'10"E) has fourteen (14) forest reserves as part of her vegetative endowment. The
primary and destructive activity going on at these sites is wood cutting/lumber business and this activity has be-
come a threat to the existing biodiversity of the communities around the studied area. The culture of replanting
is next to non-existent and with the establishment of industries as well as the existence of green house gas (GHG)
generating activities; there is imminent risk exposure to the environment.
Guesstimates of carbon stocks and stock changes in tree biomass are essential for keying into the United Na-
tions Framework Convention on Climate Change (UNFCCC) programme and as required by Kyoto Protocol as
well as for carbon credit trading. This research is the first phase of assessment of carbon sequestration potential
of tree species found within forest reserves and sites in Benue State.
2. Methodology
Sampling: Ten (10) sampling locations were identified and used in this investigation from two local govern-
ment area namely: Gwer west and Makurdi. In Gwer west, Nagi was chosen as the sampling location due to its
forest reserve with rural low emission area. Similarly, in Makurdi, Agan and Makurdi metropolis were chosen as
sampling location with mild to heavy traffic emission areas. A total of four thousand two hundred (4200) trees
belonging to twenty (20) different tree species were involved: Gmelina arborea, Tectona grandis, Anacardium
occidentale L., Sarcocephalus latifolius, Anogeisus leiocarpa, Khaya senegalensis, Maranthes polyandra, Stry-
chnos spinosa and Detarium microcarpum. Others are: Parkia biglobosa, Eucalyptus globules, Albizia lebbeck,
Delonix regia, Schefflera actinophylla, Azadirachta Indica, Mangifera indica, Polyalthia longifolia, Ficus ben-
jamina, Persea americana and Elaeis guineensis.
Analytical Method: Using non-destructive method, the mean above and below ground organic carbon
(tones/tree) and total organic carbon of each species of tree was calculated. Carbon enters the soil as roots, litter,
harvest residues, and animal manure. Carbon is stored primarily as soil organic matter (SOM) and this was de-
termined by the Walkley-Black procedure (SSSA, 2001) and the carbon stock was calculated with the formula =
C (%)/100 × soil bulk density × area (1 ha) × soil depth (Figure 1).
2.1. Diameter at Breast Height (DBH) and Tree Height (TH)
DBH was calculated by measuring the tree Trunk Circumference at 1.3 m from the ground for each tree with
circumferences greater than 10 cm while direct measurement neglecting height from ground was done for trees
with circumference less or equal to 10 cm (Figure 2).
TH was obtained by direct measuring with surveyors’ tape by climbing, aided by a pole and confirmation us-

I. S. Eneji et al.
159
ing calculation with Thiodolite angle and sides calculation (Figure 3).
The angle between the tree top and eye view at breast height angle (α) is taken into consideration for tree
height measurement and height of the tree is calculated. Considering the angle ACB between tree top and the
distance (b) at the point of observer at DBH, the tree height was calculated if α is the angle between eye view
and top of the tree, a is the height of the tree in feet, c is the slope between tree and eye view, b is the distance in
feet between tree and observer and h is height of horizontal plane of Thiodolite instrument, then the height of
tree (H) is calculated by the following formulae:
H = h + b tan α
2.2. Determination of Biomass and Carbon Dioxide Sequestered by Tree
We adopted the method recommended by Chavan and Rasal (2010) with slight modification into five stages as
follows:
1) Total (green) weight of tree based on tree species for tropical forest species, the weight of a tree is:
W = Above-ground weight of the tree in kilogram (kg); D = Diameter of the trunk in inches; H = Height of
tree in Meters. Hence, for trees with D ≤ 10: W = 0.25D2H or trees with D ≥ 11: W = 0.15D2H. The root system
weighs about 20% as much as the above-ground weight of the tree. Therefore, to determine the total green
weight of the tree, multiply the above-ground weight of the tree by 120%.
2) Dry weight of tree based on an extension publication from the University of Nebraska (Chavan and Rasal, 2010).
The dry weight of the tree was calculated by multiplying the weight of the tree by 72.5%.
3) Weight of carbon, The average carbon content is generally 50% of the tree’s total volume (DeWald et al., 2005).
Therefore, the weight of carbon in the tree was calculated by multiplying the dry weight of the tree by 50%.
4) Weight of carbon dioxide sequestered (CO2 is composed of one molecule of Carbon and 2 molecules of
Oxygen and The atomic weight of Carbon is 12.001115; The atomic weight of Oxygen is 15.9994). Hence,
weight of CO2 is C + (2 X O) = 43.999915, while the ratio of CO2 to C is 43.999915/12.001115 = 3.6663.
Therefore, to determine the weight of carbon dioxide sequestered in the tree, we multiplied the Weight of carbon
in the tree by 3.6663 (Birdsey, 1992).
5) Weight of CO2sequestered in the tree per year was calculated by dividing the weight of carbon dioxide se-
questered in the tree by the age of the tree.
Statistical analysis was carried out using Genstat sp 18 package. The procedures used include summary statis-
tics and linear regression.
3. Results and Discussion
Assessment of carbon sequestration and storage potential of 4200 trees belonging to twenty (20) tropical tree
species found within a local forest reserve and other sites in Makurdi Benue State of Nigeria was investigated.
Carbon storage and sequestration potential of trees within Benue is presented from a rural traffic low emission
area (Table 1), a mild to heavy traffic area (Table 2) and a heavy traffic high emission township (Tables 3-10),
respectively. The relationship between dry weight of the studied trees and total sequestered CO2 is shown in
Figure 4, while the relationship between heights of the studied trees to the total amount of CO2 sequestered
(Figure 5), interprets the findings.
Figure 1. Soil sample collection method, * = Sampling point.

I. S. Eneji et al.
160
Figure 2. Diagrammatic representation of tree measure-
ment methodology (Chavan, 2010).
Figure 3. Tree height measurement by Thiodolite at
DBH (SSSA, 2001).
Table 1. Assessment of tree species from Nagi, Gwer West (rural low emission area).
S/N Sp ec i es Number TH (m) DBH
(in ch es )
Weight from tree (kg)
Total (green) Dry Ca rbon CO2
sequest ered
Average CO2
sequest ered
1 Gmelina arborea 136 20.0 29. 7 3,164.8 1,912.0 956.0 9,702.0 71.3
2 Sarcocephalus latifolius 68 6.9 2 5.1 779.4 470.9 235.5 2,390.7 35.2
3 Parkia biglobosa 12 12.0 2 1.5 998.5 603.2 301.6 3,050.6 254.2
4 Anogeisus leiocarpa 12 6.2 51.8 3,005.3 1,815.7 907.9 9,148.9 762.4
5 Tectona grandis 248 10.0 21. 7 844.5 510.2 255.1 2,589.6 10.4
Total 4 76 5 5.1 149.8 8,792.5 3,682.0 2,656.1 26,881.8 1,133.5

I. S. Eneji et al.
161
Table 2. Assessment of tree species from Toll Gate, Makurdi-Lafia road (mild to heavy traffic area).
S/N Spec i es Number TH (m) DB H
(in ch es )
Weight from tree (kg)
Total
(green) Dry Car bon CO2 sequest ered
Average CO2
sequest ered
1 Tectona grandis 156 10.4 25.1 1,181.3 713.7 356.9 3,603.3 23.1
2 Maranthes polyandra 60 7.5 22.2 663.5 400.9 200.5 2,032.8 33.9
3 Sarcocephalus latifolius 4 8.2 19.1 539.0 449.2 224.5 1,645.1 411.3
4 Strychnos spinosa 4 6 .9 15.0 279.5 168.8 84.4 853.8 213.5
5 Detarium microcarpum 24 11.0 27.9 1,542.4 931.8 465.9 4,708.9 196.2
6 Gmelina arborea 212 12.0 20.1 869.2 525.1 262.6 2,655.6 12.5
7
Anacardium occidentale
L. 8 10.0 44.0 3,476.9 2,100.6 1,050.3 10,646.9 1,330.9
TOT A L 468.0 66.0 173.4 8,551.8 5,290.1 2,645.1 26,146.4 2,221.4
Table 3. Assessment of tree species from Makurdi local government township area (high emission area).
S/N Sp ec i es Number TH (m) DBH
(in ch es )
Weight from tree (kg)
Total
(green) Dry Carbon CO2 sequest ered
Average
CO
2
sequest ered
1 Eucalyptus globulus 8 22.5 100.2 40,694.6 2 4,566 .7 12, 283 .4 124 ,233. 1 15, 529 .1
2 Delonix regia 368 7.3 47.9 3,002.3 1,813.9 907.0 9,211.1 25.0
3 Albizia lebbe ck 48 8.1 48.8 3,443.9 2,080.7 1,040.4 10,608 .3 221.0
4 Schefflera
actinophylla
156 10.0 41.9 3,152.6 1,904.7 952.4 9,654.9 61.9
5 Parkia biglobosa 12 10.0 76.9 10,630.7 6,422.7 3,211.4 32,521.6 2,710.1
6 Gmelina arborea 32 10.3 77.1 10,956.0 6,619.3 3,309.7 33,671.7 1,052.2
7 Azadirachta Indica 20 15.2 81.2 18,037.0 1 0,897 .6 5,448.8 55,115.7 2,755.8
8 Mangifera indica 24 14.0 106.1 28,362.0 17, 135.2 8,567.6 86,671.8 3,611.3
9 Polyalthia longifolia 16 10.8 18.8 683.5 413.0 206.5 2,099.2 131.2
10 Ficus benjamina 32 6.8 35.7 1,560.9 943.1 471.6 4,766.1 148.9
TOTAL 7 16 115.0 634.6 120,523.5 7 2,796 .9 36, 398 .8 368 ,553. 5 2 6,246 .5
Table 4. Assessment of tree species from Wurukum Round About to School of Remedial Studies Junction.
S/N Sp ec i es Number TH (m) DBH
(in ch es )
Weight from tree (kg)
Total
(green) Dry Car bon CO2 sequest ered Average CO2 sequest ered
1 Fla mbouyan t 140 9.3 5 1.4 4,443.2 2,684.5 1,342.3 13,512.3 96.5
2 Umbrella tree 60 10.2 39.1 2,806.0 1,695.3 847.7 8,575.8 142.9
3 Albizia 8 18.5 87.7 2 5,618 .4 15, 477 .7 7,738.9 78,251 .1 9,781.4
4 Gmelia na 28 19.9 89.5 28,644 .6 17, 306.1 8,653.1 87,663.4 3,130.8
5 Eucalyptus 4 25. 0 65.2 19, 104.5 1 1,542 .3 5,771.2 58,446.0 14, 611 .5
6 Neem 20 15.8 61.0 10, 563 .5 6,382.1 3191.1 32,332 .3 1,616.6
7 Pea 16 6.5 5 5.1 3,556.4 2,148.7 1,074.4 10,852.7 678.3
8 Cocoanut tree 8 2 2.5 57.6 1 3,455 .0 8,129.1 4,064.6 41,053.2 5,131.7
9 Mango 12 16.7 90.2 24, 422.7 1 4, 755.4 7,377.7 74,722.1 6226.8
10 Cashew 16 19.5 119.3 49,945.2 30, 175.2 1 5,087 .6 152 ,62 8.2 9,539.3
11 Masquerade 12 18.3 40.1 5,304.4 3,204.8 1,602.4 16,183 .0 1,348.9
TOT A L 3 24 182.2 756.2 187,86 3.9 1 13 ,501. 2 56,751 .0 574 ,220. 1 52,304 .7

I. S. Eneji et al.
162
Table 5. Assessment of tree species from Wurukum Round about to Low level Round about.
S/N Sp ec i es Number TH
(m) DBH (in ch es )
Weight from tree (kg)
Total
(green) Dry Carb on CO2 sequest ered
Average CO2
sequest ered
1 Delonix regia 352 7 .1 4 8.6 3,033.3 1,832.6 916.3 9,222.5 26.2
2 Schefflera actinophylla 12 8.0 30.1 1,302.3 786.8 393.4 3,986.1 332.2
3 Azadirachta Indica 28 17.0 125.3 48,038.4 2 9,023 .0 14, 511 .5 146 ,781. 2 5,242.2
4 Persea americana 12 11.0 8 1.9 13, 263.6 8,013.0 4006.5 40,577 .0 3,381.4
5 Gmelina arborea 12 20.0 128.8 59,730.3 3 6,087 .0 18, 043.5 1 82 ,465. 6 15, 205 .5
6 Mangifera indica 8 11.5 8 5.2 15, 027 .9 9,079.4 4,539.7 45,908 .8 5,738.6
7 Anacardium occidentale L 16 14.3 87. 7 19, 733 .1` 1 1, 922.0 5,961.0 60,486.0 3,780.4
8 Eucalyptus globulus 8 16.0 72.7 15,211 .2 9,190.1 4595.1 46,505.9 5,813.2
TOT A L 4 48 104.9 660.3 175,340.1 1 05 ,933. 9 52, 967 .0 535 ,933. 1 3 9,519 .7
Table 6. Assessment of tree species from low level Round about to high level Round about in Makurdi.
S/N Speci es Number TH (m) DBH
(in ch es )
Weight from tree (kg)
Total
(green) Dry Carb on CO2 sequest ered
Average CO
2
sequest ered
1 Delonix regia 440 5.8 4 9.9 2,578.1 1,557.6 778.8 7,942.3 18.1
2 Schefflera actinophylla 24 9.7 42. 6 3,070.4 1,909.2 954.6 9,680.8 403.4
3 Polyalthia longifolia 12 5.3 1 8. 0 312.2 188.6 94.3 944.4 78.7
4 Albizia lebb e ck 16 11.3 58. 9 7,023.2 4,243.2 2,121.6 21,559 .0 1,347.4
5 Mangifera indica 4 12.0 100.2 21,704.2 13, 112.9 6,556.5 66,257.6 1 6,564 .4
6 Persea americana 12 8.0 40.1 2,315.8 1,399.1 699.6 7,074.5 589.5
TOTAL 508 51.4 309.7 37,003.9 22, 410.6 1 1,205 .4 113 ,45 8.6 1 9,001 .5
Table 7. Assessment of tree species from high level to B-Division Junction in Makurdi.
S/N Spec i es Number TH (m) DBH
(in ch es )
Weight from tree (kg)
Total
(green) Dry Carbon CO2 sequest ered
Average CO2
sequest ered
1 Schefflera actinophylla 144 8.3 4 1. 5 2,578.9 1,558.1 779.1 7,861.3 54.6
2 Delonix regia 132 6 .6 6 3.4 4,800.4 2,900.3 1,450.2 14,589.5 110.5
3 Gmelina arborea 8 16.0 168.6 81,822.0 49, 434.2 2 4,717 .1 2 50,12 3.4 3 1,265 .4
4 Elaeis guineensis 4 15.0 191.4 98,935.5 5 9,773 .5 2 9,886 .8 302 ,199. 9 7 5,550 .0
TOT A L 2 88 45. 9 464.9 188,135. 8 113 ,66 6.1 5 6,833 .2 574 ,30 8.0 7 8,841 .5

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Table 8. Assessment of tree species from low level Round about to State house in Makurdi.
S/N Spec i es Number TH
(m) DBH (in ch es )
Weight from tree (kg)
Total
(green) Dry Ca rbon CO2 sequest ered
Average CO2
sequest ered
1
Anacardium occidentale
L
.
4 5.0 3 1.9 916.5 553.7 276.85 2,798.2 699.6
2 Delonix regia 440 6.1 6 2. 5 4,257.6 2,572.3 1,286.2 13,104.2 29.8
3 Gmelina arborea 28 10.3 60.6 6,805.3 4,111.5 2,055.8 20,801.8 742.9
4 Mangifera indica 12 25.0 250.8 282,956.0 170 ,953. 0 85,476 .5 8 64,79 7.3 72, 066 .4
5 Persea americana 4 25.0 191.4 164,892.0 99,622 .5 49,811 .3 5 03,66 6.6 125 ,91 6.7
TOT A L 4 88 71.4 597.2 459,827. 4 107 ,031. 0 138,90 6.7
1,405,168.1
199,45 5.4
Table 9. Assessment of tree species from Wurukum Round about to Guarantee Trust Bank Junction.
S/N Sp ec i es Number TH (m) DBH
(in ch es )
Weight from tree (kg)
Total
(green) Dry Carb on CO2 sequest ered
Average CO2
sequest ered
1 Albizia lebbe ck 8 7.0 5 5.3 3,855.6 2,329.4 1,164.7 11,772.5 1,471.6
2 Delonix regia 388 5 .1 4 7.6 2,064.8 1,247.5 623.8 6,354.8 16.4
3 Mangifera indica 4 10.0 5 0. 1 4,521.8 2,731.9 1,366.0 13,803 .7 3,450.9
4 Elaeis guineensis 16 8.0 129.7 24,233.5 1 4,641 .0 7,320.5 74,009.8 4,625.6
5 Persea americana 4 4 .0 4 0. 1 1,157.9 699.6 349.8 3,537.3 884.3
6 Azadirachta Indica 4 1 3. 0 115.3 31,096 .3 18, 787.0 9,393.5 95,043.2 2 3,760 .8
7 Eucalyptus globulus 20 25.0 108.3 52,742.9 31, 865.5 1 5,932 .8 1 61,25 6.1 8,062.8
8 Parkia biglobosa 16 12.8 94. 0 20,269 .1 12, 245 .9 6,123.0 62,199 .2 3,887.5
9 Schefflera actinophylla 20 9.2 47. 6 3,754.5 2,268.3 1,134.2 11,463.6 573.2
TOT A L 4 80 94.1 688 143 ,696. 4 8 6,816 .1 43, 408.3 4 39 ,440. 2 46, 213 .1
Table 10. Assessment of tree species from Police headquarters Round about to Federal Medical Centre in Makurdi.
S/N Spec i es Number TH (m) DBH
(in ch es )
Weight from tree (kg)
Total
(green) Dry Carbon CO2 sequest ered
Average CO2
sequest ered
1 Delonix regia 172 5.8 4 7.1 2,308.4 1,394.7 697.4 7,076.0 41.1
2 Albizia lebbe ck 92 8.6 5 3.6 4,447.9 2,687.3 1,343.7 13,587.7 147.7
3 Mangifera indica 4 15.0 200.5 108,52 3.0 6 5,566 .2 32, 783 .1 331 ,618. 9 82,904 .7
4 Gmelina arborea 4 12.0 6 2. 7 8,477.5 5,121.5 2,560.8 25,943 .9 6,486.0
5 Schefflera actinophylla 36 6.1 40. 1 1,768.7 1,068.6 534.3 5,394.3 149.8
6 Persea americana 12 7.5 69.2 6,458.3 3,901.8 1,950.9 19,751.2 1,645.9
7 Azadirachta Indica 8 9.0 60.1 5,859.3 3,539.9 1,770.0 17,877.7 2,234.7
TOTA L 328 64.00 533.30 1 37,84 3.10 8 3, 280.0 0 41,639.3 0 421 ,24 9.70 93,609 .90

I. S. Eneji et al.
164
4. Discussion
The total amount of CO2 sequestered at the studied areas is presented from the lowest locations as; Low level
roundabout to State House roundabout (1,405,168.1 kg); High level to B-Division Junction (574,308.0 kg);
Wurukum round about to SRS Junction (574,220.1 kg); Wurukum round about to Low level roundabout
(535,933.1 kg); Wurukum round about to GT Bank Junction (439,440.2 kg); Police headquarters round about to
Federal Medical Center (421,249.7kg); Benue State University Teaching Hospital to Wurukum round about
(368553.5 kg); Nagi-Naka, Gwer West Local Government Area (rural traffic low emission area 26881.8 kg);
Toll Gate, Agan Village, Makurdi-Lafia road (mild to heavy traffic area 26146.4 kg); Low level round about to
High level round about (113,458.6 kg).
The relationship between the dry weight of trees and total sequestered CO2 in various locations within areas
under investigation is shown in Figure 4. There is observed much higher level of CO2 sequestered in location 8,
with a value of 1,405,168.1 kg. This may be connected to the nature, the age and specie of the trees, and the lo-
cation as is corroborated by earlier works, with dominant species of sequestered CO2 at the site being Mangifera
indica and Persea americana. The observed high value may be related to their broad leaves and thick vegetative
cover resulting from the natural cluster, especially the Persea americana. This area stretches from low level
round about to State House round about designated as part of “high traffic area”. Figure 1 also presents a gener-
ally observed trend that there is a progressively direct relationship between the dry weight of trees and the se-
questered CO2, as represented by trees on the plot and the corresponding rectangles (Gibbs et al., 2007).
From the Tables, it is observed that trees species like Anogeisus leiocarpa, Mangifera indica, Parkia biglo-
bosa, Azadirachta Indica, Anacardium occidentale, Eucalyptus globulus and Elaeis guineensis have more
amount of carbon dioxide sequestered in them within the township area. While within the low emission area like
Nagi, Naka, Anogeisus leiocarpa recorded the highest sequestration of CO2 and Tectona grandis with the lowest
(762.4 kg and 10.4 kg) respectively. For the Toll Gate area which is a medium emission area, Anacardium occi-
dentale recorded the highest with Gmelina arborea having the lowest (1,330.9 Kg and 12.5 kg) respectively.
Meanwhile, along Gboko road, Mangifera indica has the highest and Schefflera actinophylla the lowest (3611.3
kg and 61.9 kg) respectively.
Along Makurdi-Lafia road, Eucalyptus globulus recorded the highest with Delonix regia having the lowest
(14611.5 kg and 96.5 kg). From Wurukum round about to low level round about, a total amount of 535,933.1 kg
of CO2 was sequestered by the trees which are relatively smaller than that obtained along location 8 with Gme-
lina arborea absorbing the highest (182,465.6 kg) and the Schefflera actinophylla having the lowest (3,986.1 kg).
Figure 4. Relationship between dry weight and total sequestered CO2 of a tree. Keys: 1. reps.
Nagi. ; 2. reps. Toll gate.; 3. reps. BSUTH to Wurukum; 4. reps. Wurukum to SRS; 5. reps.
Wurukum to Low level; 6. reps. Low level to High level; 7. reps. High level to B-Div; 8. reps.
Low level to State House; 9. reps. Wurukum to GT Bank; 10. reps. Police hdqrt to F. M. C.

I. S. Eneji et al.
165
Figure 5. Relationship between height of tree against total amount of
CO2 sequestered. Triangle reps. Tree height while squares reps. Amt.
Of CO2 sequ estered.
This observed general low absorption along location 5 can be attributed to the relatively scanty number of trees
planted as well as the non existence of species like Mangifera indica with broad leaves and consequent thick
vegetative cover, having known that thickness of cover and area of cover influences amount of absorbed CO2 by
trees. In contrast to the observed low sequestration by the Schefflera actinophylla, the Delonix regia with a total
no of 352 sequestered only 9,222.5. This brings to light the fact on individual basis, Schefflera actinophylla with
individual sequestration of 332.2 kg, is a better candidate for sequestration than Delonix regia with individual
sequestration of 26.2 kg. This substantiates the fact that the broader the leaves, the thicker the crown cover and
consequently the denser the cluster; the more CO2 sequestered by trees, this aligns with earlier reported works
(Rowntree and Nowak, 1991).
Figure 5 in trying to establish a relationship (P > 0.05) between tree height and CO2 sequestration, show that
there is no significant direct relationship between tree height and CO2 sequestration although the height of a tree
contributes to the volume of the tree which can be related to the mass and consequently the relative CO2 seques-
tration potential of the tree (Rowntree, 1984). This is buttressed by the r2 value of 0.266. Noting that the closer
the r2 value to whole number 1, the more directly the relationship exists between the factors and more perfect the
line of best fit. The gradient of the scattered plot is 67898 and equation for the graph is y = 67898x + 75095. The
high value of the gradient is also an indication of the deviation from a linear best fit linear regression.
5. Conclusion
This preliminary evaluation strategically positions (guinea savanna) as found in Benue State in line for
UNFCCC and Kyoto carbon credit trading while substantiating the importance of preserving our indigenous
forest reserves. This is because recent importance has been attached to emissions reductions from tropical de-
forestation in future climate change policy (Rowntree, 1984). The United Nations Framework Convention on
Climate Change recently agreed to study and consider a new initiative, led by forest-rich developing countries,
that calls for economic incentives to help facilitate reductions in emissions from deforestation in developing
countries (REDD). This is a proposal to provide financial incentives to help developing countries voluntarily
reduce national deforestation rates and associated carbon emissions below a baseline.
This work has brought to bear the fact that CO2 emission within our local environment can be effectively se-
questered by planted trees more so the landscaping of our major intra city motor ways by planting of mostly
broad leaved trees will to a great extent mitigate against expunged CO2 gases from converted CO gases emitted
from automobiles with consequent reduction in health and environmental related issues.
The result has also presented a guide on the type of tree species that ought to be planted for the sequestration
of CO2 and CO gases for effective sequestration purpose. Such trees as Mango, Umbrella tree and other broad
leaved species can be planted 20 or more meters away from the pedestal path along our city ways. These species
of trees will not only aid in CO2 sequestration but also provide adequate shade and food for the populace.

I. S. Eneji et al.
166
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