The biological and ecological studies of A. drepanolobium: the floristic composition in A.rndrepanolobium wooded grassland, soil properties, seed production, seed dispersal, soil seedrnbank, percent seed germination at different treatments, capacity of coppicing , and itsrninteractions (symbiosis) with ants, insects and microbes were investigated in four A.rndrepanolobium wooded grassland sites in Negele Borana , Oromiya Regional State, S.rnEthiopia.rnThe results indicated that in A. drepanolobium wooded grassland 114 plant species werernidentified. Of these 70.2 %, 23.7% and 6.1% were herbs, trees/shrubs and climbersrnrespectively. More over, 33.3 % were forage species whereas 14.4% and 2.6% had socioeconomicrnand medicinal importance respectively. Asteraceae, Fabaceae and Poaceae havernconstituted 36 % of the total number of species. The number of species was found to bernsmaller than previous studies on non- A. drepanolobium wooded grassland of the study area.rnThis may suggest the impact of bush encroachment by A. drepanolobium, which had a meanrndensity of 1798 plants/ hectare with a large number of individuals at the younger stage. Thernsoils studied had higher proportion of clay (> 30 %) with properties that favor the growth ofrnmost plant species. An average of 2417 Â± 23 (X Â± SE) seed production per plant wasrnencountered, and only 1 Â± 0.4 (X Â± SE) trees bore seeds in average per plot. Seeds are mainlyrndispersed by wind. 267 seeds (8.3 Â± 2.6 seeds /m 2) were found only at the litter layer andrnnone in mineral soil layer. There was statistically significant difference in percentrngermination among treatments [F (5, 17), P < 0.05]. Fast rate and higher percent germinationrnwas achieved by scarification treatments whereas dry heat treatment (90 oC) and moist heatrn(98 oC for greater than 30 minutes) resulted in almost all mold outgrowths after a weekâ€™srnperiod. Tukeyâ€™s HSD indicated that moist heat treatments didnâ€™t improve the percentagerngermination. High percent germination of a control experiment within weekâ€™s time mayrnsuggest the absence of pronounced seed dormancy in the study species. There is nornstatistically significant difference among stumping treatments both in number and in height ofrncoppice but the coppice number and height increased down to a tree height (soil surface).rnFour A. drepanolobium occupant ant species (3 Crematogaster and 1 Tetraponera species)rnwere identified. However, a black cotton soil habitat hosted only 2 Crematogaster species.rnAlthough each tree was occupied by a single ant species, Crematogaster mimosae occupiedrnthe largest proportion (85%) of seed bearing trees. The mutualistic association ofrnCrematogaster nigriceps is doubtful because this species sterilizes flower buds and newrnshoots. Two seed feeding bruchid beetles (Callosobruchus maculatus and Acanthoscelidesrnobtectus) were identified and found to reduce the reproductive vigor of the study species byrnmass predation of its seeds. A. drepanolobium was found to be nodulated by slow growingrnrhizobia called Bradyrhizobium species. There was no statistically significant difference inrnnodulation status between two soils (t at 24 df = -1.22 and P=0.268). The mean nodulernnumber and weight werern4.93 Â± 0.6 and 0.00381 Â± 0.0008 (X Â± SE) in clay soils respectively. Reduction in nodulationrnmay be due to 1) richness of clay soil in mineral elements including nitrogen 2) absence ofrnadequate aeration 3) missing of some nutrients elements such as molybdenum and 4)rnSlowness of the fixer species. From the socio-economic view point, 50% of informants declared the importance of A.rndrepanolobium, and the rest expressed their hatred for its bush encroachment impacts onrntheir surrounding. However, from the present study , it can be suggested that sterilization ofrnflower buds and young shoots by Crematogaster nigriceps ants, low soil seed bank, seedrnpredation by bruchid beetles and low recruitment being the limiting factors, further expansionrnof bush encroachment by A. drepanolobium can be managed through integrated bushrnmanagement systems such as reducing cultivation of dry season grazing areas, encouragingrntraditional rangeland management systems and applying proper land use policy, reducingrnexcess livestock, stumping late in rainy seasons and periodic burning though completernrecovery of the previous range condition is a difficult task.rnKey words: A. drepanolobium, bush encroachment, seed characteristics, Crematogaster,rnbruchid beetles.