IMPACT OF PROSOPIS JULIFLORA ON HERBACEOUS VEGETATION AND SELECTED SOIL PHYSICO-CHEMICAL PROPERTIES IN GABI-RASU ZONE, AFAR REGIONAL STATE, ETHIOPIA

Abstract

Prosopis juliflora has become serious woody weed in the fragile ecosystem of Ethiopia. In Afar Regional State, it has been affecting the livelihood of the community by aggressively and successfully invading the rangeland and outcompeting the indigenous herbaceous species. The aims of this study were to investigate the impacts of P. juliflora invasion on the composition, diversity and biomass production of herbaceous vegetation, on selected soil physico-chemical properties under its canopy and selected ecosystem services. Fifty six, (each 15m x 15m), quadrats (plots) were selected from seven sites in Amibara and Gewane Districts. The sites were categorized in to five groups: zero prosopis cover (ZPC), low prosopis cover (LPC), medium prosopis cover (MPC), high prosopis cover and very high prosopis cover (VHPC) depending on the percent of canopy cover of P. juliflora. The herbaceous species composition, diversity and biomass were determined from five (each1m X1m) randomly placed sub-quadrats within 15 m x 15 m sampling plot. 112 soil samples were collected at depths 0-20 cm and 20-40 cm systematically from four (each 5m X5m) sub-quadrats within the main quadrat for the physico-chemical analysis of the soil. A total of 77 herbaceous species were identified belonging to 20 families from the study sites. Poaceae was the most represented family with 21 species followed by Acanthaceae family with eight species. The regression analysis revealed that species richness and diversity were decreased with increasing prosopis percent canopy cover at Alaydage (R2=0.88 & 0.67), M/sedi (R2=0.89 & 0.81), Yigile (R2= 0.92 & 0.91) and Angalile (R2= 0.91 & 0.77) sites. On the other hand, the herbaceous richness and diversity increased until 40% then any further increase in percent canopy cover resulted in a decline at K/buri, Orafita and Serkamo sites. The lowest biomass production was recorded from VHPC plots at all the study sites and highest was collected from ZPC plots 148.27 g/m2, 228.60 g/m2, 262.11 g/m2 and 865.11 g/m2 in Alaydage, M/sedi, Yigile and Angalile respectively. The dissimilarity ratio of the plots was increased with increase in prosopis canopy cover. The principal component analysis depicted that clay and sand particles were the most influential environmental variables on herbaceous vegetation. The results of the soil analysis showed that bulk density significantly decreased (p<0.05) with increasing in percent canopy cover at all xvi sites except Alaydage and Angalile. Soil pH was significantly (p<0.05) different at Yegile, Orafita, Alaydage and K/buri at both depths and in M/sedi at 0-20 cm depth which was lower under VHPC than ZPC plots. EC was significantly (p<0.05) lower under VHPC than ZPC and LPC plots in all sites except Serkamo and Alaydage where no significant variation was observed. Highest OC, TN and available P were recorded in VHPC plots in Yigile, Orafita, Alaydage, Serkamo and K/buri than ZPC and LPC plots at both depths and SOCS at 0-20 cm depth. About 83.9% of the respondents’ perceived P. juliflora brought negative impacts on herbaceous plants and 46.4% agreed on the positive impacts of P. juliflora on the soil fertility. Therefore, P. juliflora had markedly negative impacts on the under canopy herbaceous species richness, diversity and biomass production while ameliorating the soil properties in vegetation dearth/scarce areas.