ABSTRACT

A research was conducted to determine the density and species composition of viable seeds buried in four forest stands of a tropical rainforest in umudike, Abia State, Nigeria. The objectives were to investigate; the changes over time in density and plant species composition of the soil seed bank in secondary forest re-growth of various ages, the vertical distribution of the soil seed bank in each of the forest stands, the relationship between soil seed bank species and the above-ground vegetation in each of the forest stand, and the relationship between soil seed banks of a Natural forest stand of 36 years and that of a Gmelina arborea plantation of the same age. Four 0.25ha stands of forest aged 6-, 18-, 36- and greater than 70 years and a 0.25ha of Gmelina arborea plantation aged 36- years were selected for the study. Soil samples were collected in the month of May, August, November 2007 and February, 2008. A total of 46 samples were taken randomly .from each forest stand and Gmelina arborea plantation. Soil samples were collected at two depths (0-5cm and 6-10cm) with an augar of 7.5cm in diameter. Seedling Emergence techniques were used to study the soil seed banks. The average density of the soil seed banks varied from 6.5 to 8.5 seedlings/rn2with 6 year forest and 70 years forest having the least and highest seedlings/rn2respectively. The forest ages had no significant difference on the size and species composition of the soil seed banks. The sampling period however, showed significant differences on the size and species composition of the soil seed banks (P > Q.05). Correlation between forest age and woody species was highly significant (P > 0.01). Forest age and total herbaceous species also showed significant difference while no significant difference existed between forest age, and total number of plant species. The correlation between soil depths and total number of seeds germinated from the forest of different ages showed negative significant relationships which ranged from r = -0.94 to r ='-0.69 at P> 0.5 and P> 0.01. These results mean that seed bank size reduced as soil depth increased. A similarly test between the above-ground vegetation and soil seed banks species of the four forest stands gave Sorensen's coefficient of community (cc) values rangin.g from Q. 16 to 0.22 with a mean of 0.18. There was no relationship between soil seed bank species and above ground vegetation. Gmelina arborea plantation recorded higher number of total seedlings and herbaceous seedlings but lower number of woody species than the Natural forest of the same age. The number of woody and herbaceous species germinated from the Natural forest and Gmelina arborea plantation were not significant.