Effect of Nypa fruticans pruning regime and soil properties on regeneration of Mangrove species (Rhizophora racemosa) in Eastern Obolo, Akwa Ibom State

Abstract

The study was conducted to evaluate the effect of Nypa fruticans pruning regimes on the regeneration of mangrove (Rhizophora racemosa) at Okorombokho in Eastern Obolo, Akwa Ibom State, Nigeria. The Nypa was pruned at a uniform height of 10 cm and the area protected with used fishing nets against infiltration by Nypa seeds in tidal floods. Mangrove plants of similar height were interplanted among pre-existing stands, out of which ten plants were tagged in each sub-plot for the measurement of plant height, leaf area index, and stem girth. Three pruning regimes (0, 4, and 6 weekly pruning (WPR) were adopted and soil samples were collected from 0-15 and 15-30 cm depths. The study was a 3x2 factorial in randomized complete block design with three replications. Soil properties showed consistent differences with depth than with pruning regimes. Bulk density (BD) was statistically similar, averaging 1.04 and 1.06 Mgm-3 in 0-15 and 15-30 cm, respectively, while saturated hydraulic conductivity (Ksat), respectively averaged 0.64 and 0.27 cm h-1 . Electrical conductivity (EC), available phosphorous (Av.P) and base saturation (BS) were significantly (p≤0.05) greater in 4WPR (5.77 dS m-1 ; 30.07 mg g-1 ; 85.4%) than 6WPR (4.54 dS m-1 ; 25.82 mg g1 ; 76.2%) and 0WPR (3.57 dS m-1 ; 23.02 mg g-1 ; 74.3%). Plant height (PH) of mangrove averaged throughout the study was significantly (p≤0.05) greater in 4WPR (80.3 cm) than 0WPR (62.5 cm) but similar to 6WPR (73.4 cm). Stem girth (SG) of mangrove was similar but in the order 4WPR (1.06 cm)>6WPR (0.98 cm)>0WPR(0.86 cm). The pattern of variation in other mangrove growth parameters was similar to plant height and stem girth. The study also showed that PH and SG were negatively correlated with sand, Av.P, and EA but positively correlated with silt and clay, EC, and BS. Results indicated that mangrove species (Rhizophora racemosa) growth was optimum 4WPR than 0WPR and 6WPR and could, therefore, be recommended as a management practice for controlling the growth of Nypa fruticans and regenerating mangrove (Rhizophora racemosa) in the study area.