Characteristics and Diversity of Black Mangrove (Avicennia germinans) Pneumatophores in a Deforested and Sand-Filled Forest at Eagle Island, Niger Delta Nigeria

Abstract

Pneumatophores are a major channel of oxygen circulation in mangrove forest. It is hypothesized that soil condition, canopy cover and stagnant pool of water can influence pneumatophore growth rate. Pneumatophore characteristics i.e., abundance, diversity in root types, microbial and chemical composition in sand-filled mangrove forest was studied. Six plots were established within a rectangular area measuring 4152.24 m2 in a rand@om block design to investigate the effect of soil conditions on pneumatophore growth. A total of 9,586 pneumatophores were physically counted and differentiated into four types namely 1-branch, 2-branch, 3-branch, and 4-branch pneumatophores.  Soil samples were also collected, and the physico-chemistry determined in the laboratory. The ANOVA results shows that there is significant difference in the abundance of pneumatophore types (F3, 20 = 7.61, p<.001). The most abundant pneumatophore type is the one branch pneumatophore (n=4747) while the least is the four branched pneumatophores. The stagnant pool site with silty and muddy soil has the most abundant pneumatophore growth whereas plots in the seashore site with sandy soil has the least abundant pneumatophores. In contrast, the seashore site has the highest diversity (H=1.367), which means more root types (i.e., 2-, 3- and 4-branch) while the stagnant pool has the lowest diversity (H=0.956), which means more of the 1-branch type. Metal concentration was higher in the stagnant pool site while microbial count is higher in the seashore site.  The study shows that soil condition, canopy cover, stagnant pool plus tidal action influenced pneumatophore growth, which means that deforestation of mangrove trees leads to poor soil formation (i.e., sandy soil) and affect root formation in mangrove soil. Therefore, the destruction of mangrove trees should be discouraged to prevent soil degradation.