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Please use this identifier to cite or link to this item: http://hdl.handle.net/123456789/921

Authors: Melesse, Maryo
Advisors: Dr. Sileshi Nemomissa,Dr. EnsermuKelbessa and Dr. Tamrat
Keywords: A. drepanolobium, bush encroachment, seed characteristics, Crematogaster,bruchid beetles.
Copyright: 2003
Date Added: 23-Apr-2008
Publisher: Addis Ababa University
Abstract: ABSTRACT The biological and ecological studies of A. drepanolobium: the floristic composition in A. drepanolobium wooded grassland, soil properties, seed production, seed dispersal, soil seed bank, percent seed germination at different treatments, capacity of coppicing , and its interactions (symbiosis) with ants, insects and microbes were investigated in four A. drepanolobium wooded grassland sites in Negele Borana , Oromiya Regional State, S. Ethiopia. The results indicated that in A. drepanolobium wooded grassland 114 plant species were identified. Of these 70.2 %, 23.7% and 6.1% were herbs, trees/shrubs and climbers respectively. More over, 33.3 % were forage species whereas 14.4% and 2.6% had socioeconomic and medicinal importance respectively. Asteraceae, Fabaceae and Poaceae have constituted 36 % of the total number of species. The number of species was found to be smaller than previous studies on non- A. drepanolobium wooded grassland of the study area. This may suggest the impact of bush encroachment by A. drepanolobium, which had a mean density of 1798 plants/ hectare with a large number of individuals at the younger stage. The soils studied had higher proportion of clay (> 30 %) with properties that favor the growth of most plant species. An average of 2417 ± 23 (X ± SE) seed production per plant was encountered, and only 1 ± 0.4 (X ± SE) trees bore seeds in average per plot. Seeds are mainly dispersed by wind. 267 seeds (8.3 ± 2.6 seeds /m 2) were found only at the litter layer and none in mineral soil layer. There was statistically significant difference in percent germination among treatments [F (5, 17), P < 0.05]. Fast rate and higher percent germination was achieved by scarification treatments whereas dry heat treatment (90 oC) and moist heat (98 oC for greater than 30 minutes) resulted in almost all mold outgrowths after a week’s period. Tukey’s HSD indicated that moist heat treatments didn’t improve the percentage germination. High percent germination of a control experiment within week’s time may suggest the absence of pronounced seed dormancy in the study species. There is no statistically significant difference among stumping treatments both in number and in height of coppice but the coppice number and height increased down to a tree height (soil surface). Four A. drepanolobium occupant ant species (3 Crematogaster and 1 Tetraponera species) were identified. However, a black cotton soil habitat hosted only 2 Crematogaster species. Although each tree was occupied by a single ant species, Crematogaster mimosae occupied the largest proportion (85%) of seed bearing trees. The mutualistic association of Crematogaster nigriceps is doubtful because this species sterilizes flower buds and new shoots. Two seed feeding bruchid beetles (Callosobruchus maculatus and Acanthoscelides obtectus) were identified and found to reduce the reproductive vigor of the study species by mass predation of its seeds. A. drepanolobium was found to be nodulated by slow growing rhizobia called Bradyrhizobium species. There was no statistically significant difference in nodulation status between two soils (t at 24 df = -1.22 and P=0.268). The mean nodule number and weight were 4.93 ± 0.6 and 0.00381 ± 0.0008 (X ± SE) in clay soils respectively. Reduction in nodulation may be due to 1) richness of clay soil in mineral elements including nitrogen 2) absence of adequate aeration 3) missing of some nutrients elements such as molybdenum and 4) Slowness of the fixer species.From the socio-economic view point, 50% of informants declared the importance of A. drepanolobium, and the rest expressed their hatred for its bush encroachment impacts on their surrounding. However, from the present study , it can be suggested that sterilization of flower buds and young shoots by Crematogaster nigriceps ants, low soil seed bank, seed predation by bruchid beetles and low recruitment being the limiting factors, further expansion of bush encroachment by A. drepanolobium can be managed through integrated bush management systems such as reducing cultivation of dry season grazing areas, encouraging traditional rangeland management systems and applying proper land use policy, reducing excess livestock, stumping late in rainy seasons and periodic burning though complete recovery of the previous range condition is a difficult task.
Description: A thesis presented For the Partial Fulfillment of the Requirements of the Degree of Master of Science in Biology (Botanical Sciences)
URI: http://hdl.handle.net/123456789/921
Appears in:Thesis - Biology

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