Floristic Assessment of Natural Regeneration in an Enhanced Post-Remediated Hydrocarbon Impacted Land: A Window for Selection of Remediation Potential Native Macrophyte

Abstract

Aim: The study was aimed at revealing the composition and demographic status of forest regeneration in a post remediatied hydrocarbon impacted site by enhanced natural attenuation. Study Design: A stratified systematic transect method was used to assess the regeneration status. Place and Duration of Study: Field sampling: in parts of Edovna vegetation landscape in Emohua Local Council area of Rivers State, Niger Delta, Nigeria and site remediation activity carried out for 10 weeks. Methodology: Site remediation treatment technique, Vegetation assessment, Regeneration Assessment and data analysis were carried out. Results: The hydrocarbon activities around the SPDC marginal oil field manifold in Emuoha study area negatively impacted the Edovna forest vegetation landscape at Umuobizu resulting to a retrogressively mosaic trend condition. However, following the p-RENA process a progressively secondary succession has resulted to such classified flora: as lowland secondary vegetation mosaic nature, with heterogeneous continuum in spatial and closed horizontal assemblage of structural arrangement.     Several species of diverse life forms were found existing through diverse mode of regeneration. New species were found regenerating and were absent as adult. Greater mode of single level of regeneration than multiplier level of regeneration was exhibited among the recruits through coppicing, stolon, seedling, sapling, rhizome and tuber. The HG exhibited greater multiplier mode while HH had greater single mode of regeneration. The herbaceous recruits among the life forms revealed a secondary physiognomic unit, heterogeneous in nature as a result of the regeneration process with few regenerating shrubby recruits. A total of 115,549 seedlings and 7,825 saplings ha-1 of 96 recruits of 70 genera under 23 families were found in 800 m2 sampled site. The dominant family was Poaceae richest in species diversity (24 species). The phytosociological composition of recruits has recorded highest frequency (1675), abundance (621), density ha-1 (49,600), IVI (104.81), diversity richness (11.75) and evenness (5.96) with Herbaceous herb (HH) in highest number of regenerating recruits in the order (HH>HG>Sh>HCl>HS>ShCl>T) of habit forms. The Chamaephytes and Hemi-cryptophytes across diverse herbaceous life forms, Mesophanerophytes, Microphaneropytes, Nanophanerophytes and Hemi-cryptophytes across shrubby life forms and a megaphanerophyte tree life form were recorded among recruits. The percentage mode of regeneration had 40 recruits of herbaceous form that exhibited 12 multiplier and 4 single mode of regeneration respectively.  Four shrubby recruits exhibited 2 multiplier and 13 recruits exhibited 2 single mode of regeneration. Conclusion: The demographic status of regeneration revealed a greater seedling density than sapling density thus implying a successful and new regeneration which through protection of natural regeneration can return back to it complete forest cover again. It can be deduced in this present study that the success of natural regeneration depends on both the demographic status and rate of establishment of natural recruits which was maximal at the p-RENA landscape of the study site across the herbaceous, tree and shrubby recruits in the present study.