SOURCE:

Faculty: Biosences
Department: Botany

CONTRIBUTORS:

Ukpaka, C. Gratius
Nnabude P. C.
Mbaekwe E. I.

ABSTRACT:

For many decades now, the rich natural endowment of tropical forests particularly of south eastern Nigeria have been dwindling alarmingly, as a result of lack of sustainable management. Continuous cropping on the same land, deforestation, over harvesting of useful species, bush fires, influx of inorganic pollutants, grazing pressure, and application of high doses of artificial fertilizer were responsible for this degradation. What has survived are the watersheds, the integrity and sanctity of which is still not been respected. The need therefore to urgently restore the quality and quantity of these watersheds can no longer be overlooked. The aim of the research work therefore was to characterize and identify those factors that were responsible for the degradation of the watershed. This work was hinged on an experimental design, with interaction as follows: rainy and dry season, relief, land use, and soil depth (0-20 and 20-40) cm were tested against floral categories to determine significance. Encountered trees, climbers, shrubs, grasses and forbs species (Growth forms) were identified and recorded for each site (A-E), with the assistance of a field taxonomist, and relevant (Thonner’s analytical keys) texts. Plotless sampling technique (closest Individual method) was used to ascertain the importance values indices (IVI) of the species (Density, frequency and Biomass) at the forested site. Plot count sampling techniques (Quadrat method) was used to ascertain the Importance value indices (IVI) for the non-forested sites. Importance value indices (IVI) were obtained by summing up the relative values of density, frequency and Biomass for all species. Random sampling techniques were employed in all cases to eliminate bias. The Numerical strength of individuals of each species of each growth form was used to determine species diversities, employing Shannon Wiener diversity methods. A well structured Questionnaire (involving one hundred and fifty respondents and, rating scale, were utilized to establish the Economic relevance of each member of each species of each growth form. T-tests were used to determine the effects of the independent variables (seasons, land use, relief and soil depth) on the growth forms (IVI). Soil samples were collected from each site using soil augur instrument. The soils were bulked, air dried, sieved and subjected to laboratory analysis using Walkley Black’s methods to determine pH, percentage nitrogen, percentage organic carbon and percentage organic matter concentrations. Finally regression analysis was used to establish the contribution of each independent variable to the importance value (IVI)) of the dependent variable. The results of this study showed that 31 trees, 9 climbers, 17 shrubs, 37 grasses and 97 forbs (altogether, 191 plant species) were identified. Only 28 trees, 4 climbers, 10 shrubs, 3 grasses and 8 forbs, were highly relevant. Most species were useful as food crops, cash crops, and medicinal plants, industrial raw materials, for erosion control and as fodder crops. From personal observation, continuous cropping of the same site annually, deforestation, other less important factors impacted negatively on the study site. Less useful plant species (grasses and forbs) were more preponderant at the study site than more useful plant species (trees, climbers and shrubs). Dominant species include: Napoleana imperialis (trees), Smilax anceps (climbers), Olax viridis (shrubs), Imperata cylindrica (grass), and Mariscus alternifolia, Sida acuta, Euphorbia hirta, Aspilia africana and Amaranthus viridis (forbs). Percentage-Nitrogen, organic carbon, Organic matter and soil pH were more significant at the dry than at the rainy season, and at the 0-20, than at the 20-40 cm soil depth. Floral diversity indices were site dependent. The forest/fallow site made the highest contribution to floral development (76.71%). The grasses thrived more than all other encountered plant forms (43.03%). An ideal watershed has thousands of species per plot. It also has more of trees, climbers and shrubs that grasses and forbs. But these findings showed the opposite in terms of biodiversity, species dominance, soil indices and preponderant growth forms. It is thereby recommended that reforestation use of organic manure, planting of riparian buffers, shifting cultivation, and proper waste management should be practiced by farmers and supported by government to improve the situation. Sustainability is the key!.