124
3.5.4 Effects of Land Uses
3.5.4.1 Effects on Mangrove Forest
Several anthropogenic factors (logging, anarchic urbanization, agriculture, industrial
pollution, sand extraction) are responsible for a decrease in the mangrove cover.
Despite mangrove forests in Cameroon being legally protected since 1996 (Frame- law
n°96/012 relative to management of environment in Cameroon), there was an effective
loss of mangrove forests in the peri-urban settings of Douala since four decades and
possibly persisting beyond. Nfotabong-Atheull et al. (2013) have documented the
effect of anthropogenic land use in the reduction of mangrove cover around the Wouri
estuary both qualitatively and quantitatively. The overall accuracy of the land use/cover
map of 2009 was above 90% with an overall Kappa index of 0.87.
A trend of decrease in mangrove area and increase in human settlements was
observed between 1974 and 2009. In 1974, mangrove forests covered 51.89%
(3.01 km
2
), where as in 2003 it was 31.20% (1.81 km
2
), indicating a decrease of
39.86% over the 29-year period (Table 3.2). In the 2009 photograph, mangroves
represented 24.29% (1.41 km
2
), a decrease of 22.10% to that of 2003. Between
2003 and 2009, the coverage of less disturbed mangrove forests decreased from
0.80 to 0.29 km
2
representing a decrease of 63.75% over the 6-year period.
In contrast, the rate of change in large disturbed mangrove extend after 2003
ranged from 55.80 to 79.43%, amounting to an increase of 10.89% between 2003
and 2009. In 1974, settlements made up 18.11% (1.05 km
2
), whereas in 2009 they
extended to 28.94% (1.68 km
2
) with an increase of 60% over the 35-year period.
However, the measured rate of mangrove decrease is twice as high as that estimated
for tidal forest degradation at Mngazana estuary, Eastern Cape, South Africa
(Rajkaran and Adams 2010), which amounted to ∼21% (∼32 ha) of mangrove loss
since 1982 or to a decline of about 1 ha/year. Although none of the mangrove species present in Cameroon have been listed as threatened (Polidoro et al. 2010), populations are at risk from habitat loss (Table 3.4).
Since 2009, the introduced mangrove palm Nypa fruticans Thurnb. Wurmb. was
found growing in large open areas and along the muddy river front. This species was
also found in the field under the canopy of less degraded mangrove forests, places
where it had not been possible to accurately delineate its distribution on the airborne
imagery. The increase in areas occupied by water, road, agricultural land, sand
quarry, wood market, and other vegetation types (mainly composed of Annona glabra L., Drepanocarpus lunatus GWF Meyer, Paspalum vaginatum Sw., Anthocleista
vogelii Planch., Sesuvium portulacastrum L., and Alchornea cordifolia Müll. Arg.).
3.5.4.2 Effects on Mangrove Fauna
Though such decrease in mangrove faunal composition was recorded in the Littoral
region, many interviewees linked it to the anthropogenic disturbances prevailing.
Local people unanimously shared the opinion that trawler activities along the shore
N. Din et al.
3.5.4 Effects of Land Uses
3.5.4.1 Effects on Mangrove Forest
Several anthropogenic factors (logging, anarchic urbanization, agriculture, industrial
pollution, sand extraction) are responsible for a decrease in the mangrove cover.
Despite mangrove forests in Cameroon being legally protected since 1996 (Frame- law
n°96/012 relative to management of environment in Cameroon), there was an effective
loss of mangrove forests in the peri-urban settings of Douala since four decades and
possibly persisting beyond. Nfotabong-Atheull et al. (2013) have documented the
effect of anthropogenic land use in the reduction of mangrove cover around the Wouri
estuary both qualitatively and quantitatively. The overall accuracy of the land use/cover
map of 2009 was above 90% with an overall Kappa index of 0.87.
A trend of decrease in mangrove area and increase in human settlements was
observed between 1974 and 2009. In 1974, mangrove forests covered 51.89%
(3.01 km
2
), where as in 2003 it was 31.20% (1.81 km
2
), indicating a decrease of
39.86% over the 29-year period (Table 3.2). In the 2009 photograph, mangroves
represented 24.29% (1.41 km
2
), a decrease of 22.10% to that of 2003. Between
2003 and 2009, the coverage of less disturbed mangrove forests decreased from
0.80 to 0.29 km
2
representing a decrease of 63.75% over the 6-year period.
In contrast, the rate of change in large disturbed mangrove extend after 2003
ranged from 55.80 to 79.43%, amounting to an increase of 10.89% between 2003
and 2009. In 1974, settlements made up 18.11% (1.05 km
2
), whereas in 2009 they
extended to 28.94% (1.68 km
2
) with an increase of 60% over the 35-year period.
However, the measured rate of mangrove decrease is twice as high as that estimated
for tidal forest degradation at Mngazana estuary, Eastern Cape, South Africa
(Rajkaran and Adams 2010), which amounted to ∼21% (∼32 ha) of mangrove loss
since 1982 or to a decline of about 1 ha/year. Although none of the mangrove species present in Cameroon have been listed as threatened (Polidoro et al. 2010), populations are at risk from habitat loss (Table 3.4).
Since 2009, the introduced mangrove palm Nypa fruticans Thurnb. Wurmb. was
found growing in large open areas and along the muddy river front. This species was
also found in the field under the canopy of less degraded mangrove forests, places
where it had not been possible to accurately delineate its distribution on the airborne
imagery. The increase in areas occupied by water, road, agricultural land, sand
quarry, wood market, and other vegetation types (mainly composed of Annona glabra L., Drepanocarpus lunatus GWF Meyer, Paspalum vaginatum Sw., Anthocleista
vogelii Planch., Sesuvium portulacastrum L., and Alchornea cordifolia Müll. Arg.).
3.5.4.2 Effects on Mangrove Fauna
Though such decrease in mangrove faunal composition was recorded in the Littoral
region, many interviewees linked it to the anthropogenic disturbances prevailing.
Local people unanimously shared the opinion that trawler activities along the shore
N. Din et al.