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Table 2
Carbon concentration of litter in mangrove protected areas of Cameroon and Ghana
Country
Mangrove
forest stand
composition
Jan
Feb
Mar
Apr
May
June
July
Aug
Sept
Oct
Nov
Dec
Mean
SE
CV
(%)
Cameroon
Avicennia
47.7
47.8
47.8
47.7
47.7
47.8
47.7
47.7
47.8
47.8
47.8
47.8
47.8
0.0
0.1
Rhizophora
47.3
47.3
47.3
47.2
47.2
47.2
47.2
47.2
47.2
47.2
47.3
47.3
47.2
0.0
0.1
Mixed
47.7
47.7
47.7
47.5
47.5
48.0
47.5
47.5
48.0
48.0
47.8
47.7
47.7
0.1
0.4
Ghana
Avicennia
49.1
49.0
49.5
49.6
48.7
48.7
49.4
49.4
48.6
48.6
49.0
49.1
49.0
0.1
0.7
Rhizophora
49.3
49.3
49.1
48.9
49.2
49.2
49.7
49.7
49.6
49.6
49.5
49.2
49.4
0.1
0.5
Mixed
49.5
49.0
48.9
49.8
49.2
48.9
48.5
48.5
49.2
49.2
49.4
49.8
49.2
0.1
0.8
Carbon Stocks in Total Litterfall in Cameroon
and Ghana
and from April to October in mixed mangrove. This may be
attributed to the change from high-shedding rates to high-
leafing rate. This is further exemplified by the lower
quantity of stipules in this period (Spalding et al.
2010
;
Dahdouh-Guebas
2011
).
According to the rainfall variations in Ghana and Cam-
eroon, it appeared that the leaves and twigs/branches lit-
terfall of Avicennia, Rhizophora and mixed stands increased
with the decrease in rainfall (Fig.
14
), and obviously in the
dry season (Kairo and Bosire
2009
; Spalding et al.
2010
).
This can be explained by the fact that interstitial water
salinity, which is relatively high in the dry season, increases
stress in mangroves, resulting in increased leaf and branch
loss by the mangrove trees, indicative of their adaptive
measures to reduce water loss (Spalding et al.
2010
; Dah-
douh-Guebas
2011
; Ramsar-Mava-Unep
2012
).
Leaf production was found to be continuous throughout
the study period, which suggests that environmental con-
ditions are favourable for leaf emergence all year round,
and the stress does not appear to limit leaf production.
Similar results have been reported by Aheto (
2011
), Spal-
ding et al. (
2010
), Crona et al. (
2009
), and Dahdouh-Guebas
(
2011
). Seasonal fluctuations have been found in the lit-
terfall of several mangrove species, notably of the genera
Avicennia and Rhizophora (Spalding et al.
2010
). Litterfall
can also be observed throughout the year with little
(Lovelock et al.
2005
; Conchedda et al.
2011
) or marked
(Day and Machados
1986
; Wattayakorn et al.
1990
; Bosire
et al.
2006
; Andriamalala
2007
; Egnankou Wadja
2009
)
seasonal variations. The major flowering and fruiting sea-
sons of R. racemosa and A. germinans in Ghana and
Cameroon were mainly in the dry season (except for fruits
in Avicennia Ghana and Cameroon, and flowers in mixed
mangroves in Cameroon were highest in the dry season).
The trend of total litterfall products followed the changes of
flower and fruit litterfall products (Table
1
). It was observed
that total litterfall decreased in the rainy season. A general
trend of litterfall peaks occurring during the dry season has
been reported in a number of mangrove studies (Ochieng
and Erftemeijer
2002
; Lovelock et al.
2005
).
Carbon pools in litterfall were determined mainly using the
Kauffman and Donato (
2012
) method, where carbon con-
centrations (ranging from 46 to 50 %) are multiplied by the
biomass of litterfall in both countries (Table
2
). It appeared
that in Ghana sites the total mean carbon stock was
3,410.98 g/m
2
in Avicennia, 6,067.33 g/m
2
in Rhizophora
and 2,975.84 g/m
2
in mixed stands; while in Cameroon the
carbon stocks were 5,329.73 g/m
2
in Avicennia, 7,582.52 g/
m
2
in Rhizophora and 8,529.36 g/m
2
in mixed stands. It was
also clearly shown in Fig.
15
that the highest peak of carbon
stock mainly appeared in the dry season. From the results
above, it was shown that the period (dry season) or country
(Cameroon) with high total mean biomass of litterfall also
showed high-carbon content.
Globally, according to the rainfall variation in Ghana and
Cameroon, it appeared that the leaves and twigs/branches
litterfall of Avicennia, Rhizophora and mixed stands
increased with decreasing rainfall, then obviously in the dry
season (Figs.
3
,
7
). This can be explained by the fact that
interstitial water salinity, which is relatively high in the dry
season, increases stress in mangroves, resulting in increased
leaf and branches loss by the mangrove trees, which is
indicative of their adaptive measures to reduce water loss.
An analysis of variance (ANOVA) of vegetative and
reproductive litterfall showed very significant differences
(p B 0.0001) in twigs/branches, leaves and flowers in
Ghana and Cameroon between sites (Lovelock et al.
2005
;
Spalding et al.
2010
; Alongi
2011
; Dahdouh-Guebas
2011
).
The present study also present higher total mean litter-
fall, trees densities and carbon stocks in Cameroon sites
compare with those from Ghana with relatively lower val-
ues. The structural development of the mangrove forest was
then found to be positively related to the production of
litterfall in each country. Similar results were found in the
West and Central African Ecoregion (Baba et al.
2004
;
Bosire et al.
2006
; Ajonina
2008
; Nfotabong Atheull
2008
,
2011
; Worlanyo Aheto
2011
; Kauffman and Donato
2012
).
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