Growth performance and gum arabic production of Acacia senegal in northwest lowlands of Ethiopia

Despite the wide distribution of natural stands of Acacia senegal in Ethiopia, commercial exploitation of gum arabic is con- strained by lack of tapping and development techniques. We evaluated the gum arabic yield from natural stands of A. senegal and the growth of 6 provenances in different parts of the country. For the gum yield evalua- tion from natural stands, four tapping positions and three tapping seasons were tested in a factorial RCB design. The second experiment in Metema evaluated survival and growth of six provenances. A. senegal trees in natural stands respond well to tapping if tapped during the appropriate season and at the correct position on the tree. The mean gum yield did not vary significantly by tapping season （p=0.63）. Higher mean yield was, however, collected from trees tapped in October （96 g.tree^-1 per two harvests）. The mean yield differed significantly （p=0.009） between the tapping positions. Mean separation （ct=0.05） shows that trees tapped at mid stem gave higher yield （160 g.tree^-1 per two harvests）. The interac- tion effect of tapping season and position was not significant. Higher mean yield （（70 ± 112） g.tree^-1） was recorded in mid October-mid stem in two harvests. The second experiment indicated statistically significant difference in mean survival （p=0.0298）, height （p=0.000） and root col- lar diameter （RCD）, （p=0.012） between the six provenances. Highest survival, height and root collar diameter growth was observed from Ab- derail provenance （100%, （148±11） era, （38±11） mm, respectively）. We recommend October and mid-stem and branches as appropriate tapping season and position. We recommend planting of the Abderafi provenance for the study area due to its superior growth and survival. Our study contributes to the proper selection of provenances for plantation devel- opment and improved tapping technology for better production of gum arabic in the country.

Variations in soil properties and native woody plant species abundance under Prosopis juliflora invasion in Afar grazing lands, Ethiopia

Introduction:Pastoralism and agro-pastoralism are the major modes of life in arid and semi-arid rangelands.However,rangeland quality and quantity are rapidly deteriorating due to a number of natural and human-induced factors,one of which is bush encroachment.Little is known on how bush encroachment affects the ecosystem functions and services expressed in terms of the native vegetation composition and structure,status of the soil seed bank,soil chemical and physical properties,and the abundance of mycorrhiza spores.Methods:We assessed woody species in 64 plots distributed across four levels of Prosopis juliflora invasion(high,medium,low,and none)at two sites,Amibara and Gewane,in the Afar Region,Ethiopia.We collected composite soil samples to investigate the soil seed bank,mycorrhizal associations,and spore abundance.Results:Plant biodiversity was generally low,with eight and four woody species in Gewane and Amibara,respectively.Prosopis juliflora was dominant in highly,moderately,and lowly invaded areas while Acacia senegal dominated the non-invaded areas.The average number of P.juliflora individuals ranged from 3/ha at non-invaded areas in Gewane to 4200/ha at highly invaded areas in Amibara while the total individual number of native woody species ranged from 0 to 88/ha at highly and lowly invaded areas,respectively.The population structure of trees/shrubs in all invasion areas showed an inverted J-shaped distribution,characterized by a high abundance of small individuals.Prosopis juliflora invasion was associated with high soil OC,Na,Ca,P,bulk density,and moisture content.Herbaceous seed numbers and species richness were highest in the moderately and highly invaded areas.All sampled tree species were associated with mycorrhiza but the percentage of root length colonization by different arbuscular mycorrhizal fungus structures varied significantly(p<0.05)across invasion categories and sites.Conclusions:Our results revealed that although P.juliflora invasion negatively impacted the availability of native woody livestock forage species,it had a positive effect on most soil physical and chemical properties.Such variable effects call out for sustainable management practices when invaded areas are restored.