Ecological Studies of Obollo Afor Savanna Woodland

Abstract

Nwadinigwe, Alfreda Ogochukwu Ecological Studies of Obollo Afor Savanna Woodland Obollo Afor Savanna Woodland in Udenu Local Government Area of Enugu State, Nigeria is located near Obollo Afor-Ikem road, about 19km from the University of Nigeria, Nsukka. The 3 sites are found in between 2 hills near a diverted river course. Ecological studies of the savanna woodland revealed a floristic composition of 133 species in 46 families; 34 families; of Dicotyledons, 10 of Monocotyledons, and 2 of Pteridophytes. The percentage frequency and density determinations showed that the humid site had the highest percentage of the different plant attributes while the dry site had the lowest. The semi humid site was in between. The number of trees and shrubs recorded in the 54 plots of 100 m2 each was 1137. This gave a density of 0.211 trees and shrubs per m2, ranging from 0.33 on the humid site to 0.14 on the dry site. The results of species and plot ordination using Factor Analysis reveaed that the first axis separated the fire-tener plants and epiphytes from the fire resistant savanna species and large trees. The second axis separated herbaceous and shrubby species. The fire-tender plants, epipgytes, herbaceous and shrubby species were found in the semi-humid sites of the project area while the savanna species tend towards the drier site. When the plant attributes (the number of plants in a plot, percentage herbaceous species, percentage fire-tender plants, percentage grasses and sedges, density of trees and shrubs, percentage woody species, basal area of woody species and savanna plants) and the soil factors were plotted superimposed on the plot ordination. It was found that the that the stands on the humid and semi-humid areas had higher values for majority of the plant attrubutes and the soil factors than those in the dry site. However, the stands in the dry site had higher values for savanna plants, grasses and phosphorus. The correlation and regression analysis revealed that most of the plant attributes had positive (and negative for grasses and sedges) linear relationships with many of the soil factors with a significant correlation of p= 0.01 (and p =0.05 for PH and the plant attributes). The relationships between the humid areas (and semi-humid areas), the plant attributes and the soil factors demonstate how moisture and soil factors affect the distribution of species. The life - form determination showed that phanerophytes dominate the vegetation. Measurement of basal area of woody species whose girths at breast height were more than 5cm showed that the vegetation is young since there is a significant increase in girth-size class below 41 cm. The phenology studies showed that 70 species flowered once a year, 5 flowered twice a year while only one, Maranthes Kerstingii flowered 3 times a year, A type of crytogeal germination was observes in Parinari curatellifolia in which the apparent radicle gave rise to the '' apparent rhizomes'', which produced tiny ''scale leaves'', ''nodes'' ''internodes'' buds, numerous rootlets and roots inside the fruit mesocarp. The hiding of the 'apparent rhizomes' and the newly formed buds inside the tough fibrous fruit mesocarp may be a response of the plant to pyrophytic habit so that these organs are protected from fire attacks and damage by animals and man. The results of burning and slashing on seed germination, average herbaceous standing crop and grass tiller regeneration gave highest values for burnt plots, followed by slashed plots and lastly by the unburnt plots. The effects of temperature [250C - 300C (ambient), 800C and 1100C] storage (4 weeks to 11 weeks); watering with ash (o g/1, 5 g/1, 5g/I, 10g/I, 15g/I and 20g/I) and seed position (apical, intermediate and basal) in the inflorescence on seed germination showed that early burning temperature (800C) of bush fire significantly favoured the germination of Andropogan gayanus but retarded that of Hyparrhenia rufa, H, rufa may require a dormancy period of less than 4 weeks before germinating, whereas A. gayanus may require a domancy period of more than 4 weeks. The enhancement of germination by 1g/I ash concentration was significant at P> 0.05 for H. rufa but it did not increase the mean germination of A.gayanus seeds. Higher ash concentrations depressed the mean germination of both plants. The somatic polymorphism exhibited by H. rufa was significant at P> 0.01 while that exhibited by A. gayanus was not significant. The interaction between ash concentration and temperature was significant at P>0.05 for H. rufa. For A. gayanus the interaction between storage and temperature was highly significant at P>0.01. All other interactions were not significant. For an effective savanna management policy, it is necessary to provide adequate water supply, suitable soil factors and apply early burning strategy, which encourages light and high tree canopies, mineral recycling, seed germination, grass tiller regeneration and herbaceous production.