Environmental Engineering Reference
In-Depth Information
Table 2
Structural characteristics of mangrove woody species within the sites inventoried in southern Benin
Condition
Mean
diameter
(cm)
Max
height
(m)
Mean
height (m)
Stand basal
area (m
2
/ha)
Species
Stem density
(Stems/ha)
Max
diameter
(cm)
Stand volume
(m
3
/ha)
G
±SE
Vol
±SE
Degraded
A. germinans
733.5
16.8
5.7
4.8
3.7
1.51
0.01
4.02
0.03
Acrosticum
aurerum
300
10.4
3.1
3.9
3.1
0.34
0.01
0.58
0.02
R. racemosa
625
8.75
6.3
8.8
7.8
0.40
0.03
2.23
0.23
Total (mean)
1,508.5
19.35
3.3
9.3
3.7
2.09
0.01
6.55
0.06
Non-
degraded
A. germinans
183
21.1
10.2
13.5
10.5
1.89
0.05
12.71
0.45
R. racemosa
1,233
20.3
8.2
21.1
10.8
8.24
0.01
37.72
0.13
Total (mean)
1,416
21.1
8.5
18.6
10.7
10.14
0.01
50.42
0.13
All sites
A. germinans
550
24.8
7.2
5.1
5.9
1.64
0.01
6.92
0.15
Acrosticum
aurerum
300
10.4
3.1
3.9
3.1
0.34
0.01
0.58
0.02
R. racemosa
828
20.3
6.9
21.1
8.8
3.02
0.02
14.06
0.01
Mean
559
24.8
5.8
21.1
5.9
1.66
0.01
7.19
0.02
More degraded
Less degraded
Non degraded
Results and Discussions
2000
1800
1600
Floristic Composition, Structure, and Biometric
Characteristics of Mangrove Stands
in the Mangrove Sites Inventoried
1400
1200
1000
800
The details of floristic composition, structure, and biometric
characteristics are presented in Table
2
and Fig.
6
. Species
frequently encountered in the sites surveyed are typical
species of mangroves in West Africa, Central, and Western
bloc (Tomlinson
1986
). They are as follows: A. germinans,
R. racemosa as woody species, A. aurerum (mangrove
fern), and Paspalum vaginatus (herbaceous). The maximum
diameter was 24.8 and 20.3 cm for Avicennia and Rhizo-
phora, respectively, in non-degraded mangrove sites with
maximum height of 21 m. Standing volumes varied from
6.55 m
3
/ha in degraded mangroves to 50.42 m
3
/ha in the
non-degraded mangrove sites. Stem diameter distributions
depart from the exponential law obeyed by pristine stands
(Husch et al.
2003
) showing the disturbed nature of the sites
as reported by Daïnou et al. (
2008
). The highest stem
density of diameter between 0 and 5 cm in degraded man-
groves (Fig.
6
) compared to non-degraded indicates that the
latter were characterized by more regeneration of species
due to canopy opening. The stem density of diameter
5-30 cm in degraded mangroves was lower than that in
non-degraded, indicating high human pressure on young
and adult stems in the region.
600
400
200
0
1-5cm
5-10cm
10-30cm
Diameter
Fig. 6
Stem density-diameter distribution in mangroves of southern
Benin
Carbon Budget Within the Inventoried Sites
The carbon budget at the different sites surveyed is pre-
sented in Table
3
and Fig.
7
. The total annual carbon stock
to soil depth of one meter varied from 179.39 t/ha in non-
forested sites to 288.77 t/ha in degraded mangroves and
184.01 t/ha for non-degraded mangroves. Aboveground
biomass carbon in non-degraded sites was 35.07 t/ha, more
than five times that in degraded mangrove sites. The dis-
tribution of total ecosystem carbon stocks for the above-
ground
component
for
the
mangrove
sites
varied
from
0.82 %
for
non-forested
sites,
2.94 %
for
degraded,
and
16.01 %
for
non-degraded
sites
(Table
3
).
The
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