Abstract
This study investigated the distributional patterns of species in response to salinity gradients. The vegetation was systematically sampled using a quadrat of 50 x 10 m. Vegetation variables were measured. At depths of 0 – 15 and 15 – 30 cm, sediment samples were dug and analyzed using standard methods. Fourteen species were encountered. Rhizophora mangle and Mytragyna ciliata had highest and least density values of 6664±687.16 and 3.00±0.42 st/ha. The most frequent species were Rhizophora mangle and Nypa fruticans (100 %). Rhizophora mangle and Mytragyna were tallest (12.45±1.20 m) and shortest species (3.11±0.24 m). Elaeis guineensis and Alchornea cordifolia had the largest (1.79±0.05 m2/ha) and least (0.008±0.0002 m2/ha) basal area values. Highest crown cover value was recorded by Rhizophora mangle (9.14±0.08 m2/ha) while by Alchornea cordifolia had the least value (0.04±0.001 m2/ha). Gradient analysis revealed that Ipomoea involucrata, Paspalum vaginatum, Dracaena mannii, Piptadeniastrum africanum, Elaeis guineensis, Staudtia stipitata, Alchornea cordifolia, Terminalia superba and Mytragyna ciliata belonged to ecological group 1 with ecological optima of 8.14, respectively. Acrostichum aureum (ecological optimum of 29.32), Avicennia africana (ecological optima of 19.56 and 30.12) and Phoenix reclinata (ecological optima of 8.14 and 29.32) belonged to ecological group 4 while Nypa fruticans (ecological optima of 8.14 and 29.32) and Rhizophora mangle (ecological optima of 19.56 and 30.12) belonged to ecological group 0. This study provides information on species adaptation and performance in relation to environmental stress and will form the basis for the future and effective management of this ecosystems.
Highlights
Mangroves are plants occurring in tropical and sub-tropical coastal environments and they consist of species with good adaptations to intertidal conditions
With regards to the density of species, Rhizophora mangle dominated with mean value of (6664±687.16 st/ha) while Mytragyna ciliata had the least density value (3.00±0.42 st/ha)
Rhizophora mangle and Nypa fruticans had the highest frequency values (100 %) while the least values were associated with species such as Ipomoea involucrata (14.29 %), Staudtia stipitata (14.29 %), Piptadeniastrum africanum (14.29 %), Alchornea cordifolia (14.29 %), Terminalia superba (14.29 %) and Mytragyna ciliata (14.29 %)
Summary
Mangroves are plants occurring in tropical and sub-tropical coastal environments and they consist of species with good adaptations to intertidal conditions. The growth and distribution of such species are strongly controlled and influenced by a constellation of factors such as salinity, tidal flushing, geographical latitude, freshwater runoff, rainfall, erosion/sedimentation rates, soil quality and nutrient inputs [1] Of all these factors, salinity tends to be very dominant and most influential in this ecosystem. As a result of regular sea tidal flushing and inundations, the mangrove soil becomes highly saline and these obviously affect the zonation and growth patterns of mangroves In such scenarios, what defines the survival and distribution of the plant species is their adaptation and salt tolerance abilities to salinity. The intrinsic abilities of these species to survive harsh environmental conditions (wind action, tidal flushing and salinity) makes this ecosystem very critical for conservation
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