Invasion of Prosopis Juliflora (Sw.) DC. and its Ecological Impacts in Afar National Regional State, Northeast Ethiopia
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2020-07-18
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Addis Ababa University
Abstract
The ecological impacts of Prosopis juliflora (Sw.) DC. on ecosystem properties have been reported to be severe especially on grazing land and woodland. The objectives of this study were to quantify the land use/cover changes in Awash Fentale and Amibara districts, (2) investigate the effects of climate variability on the phenology of P. juliflora, (3) assess effects of Prosopis juliflora invasion on species composition and diversity, (4) investigate the effects of P. juliflora on soil physicochemical properties, and (5) assess effects of Prosopis juliflora on soil seed bank compositon and density. A combination of remote sensing data and field observations were used to analyze effects of Prosopis juliflora invasion on land use and land cover changes from 1986 to 2017 in Amibara and Awash Fentale districts in Afar National Regional State. Data for phenology of Prosopis juliflora including leafing, flowering, green, and mature pod proportions (%) per tree per month were collected for a year in 2017. For floristic analysis, data were collected under four distinct habitats, namely Prosopis juliflora thickets (PJT), P. juliflora mixed with native species (PJM), non-invaded woodlands (NIWLs), and open grazing lands (OGLs). Quadrats were laid using systematic random sampling technique. In each habitat, soil samples for soil seed bank were also collected from litter layer, 0–3 cm, 3–6 cm, and 6–9 cm. In Amibara and Awash Fentatle districts, during 1986–2017 area under farm land, water bodies, grassland, area invaded by P. juliflora increased, while barren and woodland areas decreased. Overall, 7886 ha of woodlands and 221 ha grazing lands were converted to Prosopis juliflora invaded land during 1986–2017 in the study area. During 2017 growing seasons, the lowest proportion of mature and green pods per tree of Prosopis juliflora were recorded in Bega (dry season), but the highest in Belg (spring) season. The highest proportion of flowering per tree was recorded in November-December, while the lowest proportion of flowering per tree was in January-February. Invasion by Prosopis juliflora significantly changed diversity, evenness and species richness. The mean values of Shannon diversity index and species richness under PJM (H’ =2.22, R= 13.94) and NIWLs (H’=2.23, R =13.44) were significantly higher than that of PJT (H’=1.96, R=11.50) and OGLs (H’=1.84, N=9.56). Invasion by Prosopis juliflora also significantly reduced density of native woody species. In this study, 102 trees ha-1 of native woody species were recorded under P. juliflora thicket, but 1252 trees ha-1 of native species were recorded under non-invaded woodlands. In Teru and Yalo districts, the mean density of soil seed bank in non-invaded grazing lands (813 ± 375 seedlings / m2) was significantly higher than the soil seed bank density of Prosopis juliflora invaded lands (545 ± 156 seedlings / m2. Invasion of Prosopis juliflora had significantly affected soil pH, exchangeable Na+, water soluble Ca2+ + Mg2+, water soluble Na+, and exchangeable sodium percentage in Teru and Yalo distrcits. Thus, invasion of Prosopis juliflora significantly increased soil pH (1.5%), but decreased exchangeable Na+ (24.2%), exchangeable sodium percentage (21.6%), and water soluble Ca2+ + Mg2+ (39.9%) than non-invaded open grazing lands. Based on these results it is concluded that Prosopis juliflora drastically alters vegetation and soil properties. If the present change continues, pastoralists grazing lands will be lost. To reverse these situations, integrated management of Prosopis juliflora should be implemented through participation of all stockholders and multidisciplinary research approaches.
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Floristic Diversity, Encroachment, Invasive, Phenology, Seed Bank, Soil Properties