This study assesses litterfall and nutrient returns to the soil in isolated stands of Persea gratissima in the rainforest zone of southern Nigeria. The study examined litter production, the concentrations of nutrients in litterfall, the returns of nutrient elements to the soil via litterfall, the relationship between litter production nutrient returns via litterfall, and determined the seasonal variations in litter production and the returns of nutrient elements via litterfall respectively. Data collection was on litterfall which was collected from February 2010 -January 2011. Data collected were statistically analyzed using the SPSS 15.0 version. Average litter production was 60.23 g/m²/yr and 77.31 g/m²/yr for the Persea gratissima and adjoining rainforest. Results of the Independent Samples T-Test revealed that there are significant differences between Persea gratissima and adjoining rainforest in litter production and returns of nutrient elements via litterfall. Except for Nitrogen, the concentrations of nutrient elements were similar. Results of Pearson's bivariate analyses showed that significant positive relationships exist between litter production and nutrients returned to the soil through litterfall at the 5% levels. However, litter production and the returns of nutrient elements vary with the seasons of the year, but the trend in the seasonal patterns of nutrient returns from Persea gratissima and adjoining rainforest is similar for K, Ca, Na and Mg. Persea gratissima return nutrients to the soil through litterfall, therefore its production should be encouraged to help in improving the soil nutrient status in rainforest areas.

In Nigeria, soil fertility restoration for improved agricultural production is a recurrent issue of immense importance mostly with her ever increasing population currently above 150 million.

This study assesses litter production, concentrations and returns of nutrient elements with respect to seasons, so as to provide empirical information on nutrient flux by the isolated exotic stands of Terminalia. Litterfall samples were collected from the isolated stands of Terminalia catappa and adjoining native rainforest which serves as control for the experimental research for 12 months. Data collected were analyzed in the laboratory and the results were subjected to both descriptive and inferential statistical analyses using the SPSS 15.0 version. Average litter production for the Terminalia catappa and the adjoining rainforest were 83.04 g/m²/yr and 77.31 g/m²/yr respectively. Results of the Independent Samples T-Test showed significant difference in litter production, nutrient concentrations and the returns of nutrient elements via litterfall between the two sample sites (P value). Both litter production and the return of nutrient elements varied with the seasons of the year. While Terminalia catappa stands produced the highest litter in the months with heavy rainfall, the adjoining rainforests produced the highest litter in the dry season months. The order of nutrient elements return via litterfall by Terminalia catappa stands was Ca > N > K > Mg > P > Na, while that of the adjoining rainforest was N > Ca > K > Mg > P > Na. Results of Pearson's bivariate analyses showed significant positive relationships between litter production and nutrients return through litterfall at the 5% levels, with the correlations ranging between 0.984-0.999 in Terminalia catappa stands and 0.944-0.991 in the adjoining rainforest. Therefore, the cultivation of Terminalia catappa which is an exotic tree species to this study area has implications in returning nutrient elements to the soils of the rainforest ecosystem.

This study is based on the ecological effects and vulnerability assessment of flooding within Udu Local Government in the Delta State region. This research adopted the survey design. Five (5) flood vulnerable communities which represent the major subdivisions in Udu were investigated. Stratified random technique of sampling was used to divide the communities into quarters for effectiveness in data collection, while simple random technique was adopted in the collection of data. Data collection was on the communities covered by flood, causative factors of flooding, and the resultant effects on human inhabitants, environment, and the prevailing economic activities within the region. Data collection was through direct field survey and the use of questionnaires. The instrument’s level of reliability was achieved at 0.89 using the test-retest method; while instrument validity was determined by experts’ judgements. Data collected were analysed using the descriptive, ANOVA and regression statistics. Results showed that the communities investigated are vulnerable to flooding; significant difference was not found in the observed causative factors of flooding among the vulnerable communities; the effect of flooding is high within the study area; the differences in the effects of flooding within the different flood vulnerable communities in the study area is not significant at 0.05 level of confidence; and no significant relationship exists between the causative factors and the effects of flooding at 0.05 level of confidence. Therefore, good settlement planning, construct of drainage, and selective terrain cultivation are recommended.