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|Title: ||BIOLOGICAL AND ECOLOGICAL STUDIES ON ACACIA DREPANOLOBIUM HARMS EX SJÖSTEDT IN BORANA ZONE OF OROMIYA REGIONAL STATE, ETHIOPIA|
|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|
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.
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)|
|Appears in:||Thesis - Biology|
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