Mangrove species distribution, abundance and restoration potential in dege mangrove ecosystem, Dar es salaam

A study was carried out in Dege Mangrove Ecosystem, south of Dar es Salaam, on transplanting mangrove seedlings in three selected sites having different levels of degradation, Site A having a clear cut area, Site B showing little disturbance and Site C showing moderate cutting pressure. Ten seedlings each of Avicennia marina, Rhizophora mucronata and Sonneratia alba were transplanted alternately in 8 rows in each of the three sites, making a total of 720 seedlings. The survival, health status and growth rates of all seedlings were assessed over a period of 15 weeks. Mangrove diversity and abundance were also determined by counting and measuring the girth at breast height of all trees, saplings and seedlings of each mangrove species in 8 plots (5 m x 5 m) in each site. As an indication of degradation, all stumps in each plot were counted and measured. Abiotic factors (substrate temperature, salinity, percent saturation capacity and organic matter content) were also measured in each plot. Five mangrove species were observed in Dege mangrove forest, i.e., Rhizophora mucronata, Avicennia marina, Ceriops tagal, Sonneratia alba and Bruguiera gymnorrhiza. Mangrove species diversity and basal area were higher in Site B, attributed mainly to low cutting pressure and high substrate organic matter. Site A had the lowest diversity and basal area, due to high cutting pressure. Transplanted seedlings of Rhizophora mucronata showed faster growth rates than did Avicennia marina and Sonneratia alba in all study sites, though there were no obvious differences in survival and health status among the three species. Survival and health status of transplanted seedlings were generally highest in Site B due to higher substrate organic matter and greater basal area/canopy cover, which provided shade, decreasing substrate temperature and salinity. Survival and health status were generally lowest in Site A, since the area had been clear cut, leading to high substrate temperature and salinity.