Effect of Soil Types on Growth, Survival and Abundance of Mangrove (Rhizophora racemosa) and Nypa Palm (Nypa fruticans) Seedlings in the Niger Delta, Nigeria

The invasion of nypa palm into mangrove forest is a serious problem in the Niger Delta. It is thus hypothesized that soil  will influence the growth, survival and abundance of mangrove and nypa palm seedlings. The objective was  to compare the growth, survival and abundance of both species in mangroves, nypa palm and farm soils (control). The seeds were planted in polyethylene bags and monitored for one year. Seed and seedling abundance experiment was conducted in the field. The result indicates that there was significant difference in height (F_{3, 162} = 4.54, P<0.001) and number of leaves (F_{3, 162} = 21.52, P<0.0001) of mangrove seedlings in different soils, but there was no significant difference in diameter (F_{3, 162} = 4.54, P = 0.06). Height of mangrove seedling was  influenced by highly polluted soil (P = 0.027) while number of leaves was  influenced by farm soil (P = 0.0001). On the other hand, mangrove seedlings planted in farm soil were taller (7.8±0.7 cm) than seedlings planted in highly polluted (7.7±0.4 cm), lowly polluted (6.3±1.4 cm)  and nypa palm (6.0±0.8 cm) soils whereas Nypa palm seedlings planted in farm soil were the tallest (42±3.4 cm) followed by mangrove-high (38.8±5.8 cm), mangrove-low (34.2±cm) and nypa palm (21.1±1.0 cm) soils. Furthermore, species abundance of the different growth stages of mangrove and nypa palm seedlings were significantly different (F_{1, 37} = 3.07, P = 0.04). Nypa palm seedlings outnumbered mangroves (27:1) and had higher overall survival rate (0.48) than mangroves seedlings (0.35) in all soils. This implies that nypa palm has competitive advantage over mangrove in mangrove soil.