Addis Ababa University, Graduate Programs
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ADDIS ABABA UNIVERSITY, GRADUATE PROGRAMS COLLEGE OF NATURAL AND COMPUTATIONAL SCIENCES DEPARTMENT OF PLANT BIOLOGY AND BIODIVERSITY MANAGEMENT Invasion of Prosopis juliflora (Sw.) DC. and its ecological impacts in Afar National Regional State, Northeast Ethiopia WAKSHUM SHIFERAW GEMEDA Addis Ababa, Ethiopia July 2020 Invasion of Prosopis juliflora (Sw.) DC. and its ecological impacts in Afar National Regional State, Northeast Ethiopia Wakshum Shiferaw Gemeda A Thesis Presented to the Graduate Programs of the Addis Ababa University in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Plant Biology and Biodiversity Management Addis Ababa University Addis Ababa, Ethiopia July 2020 ii ADDIS ABABA UNIVERSITY GRADUATE PROGRAMMES This is to certify that the thesis prepared by Wakshum Shiferaw Gemeda, entitled: Invasion of Prosopis juliflora (Sw.) DC. and its ecological impacts in Afar National Regional State, Northeast Ethiopia submitted in Partial fulfillment of the requirements for the Degree of Doctor of Philosophy in Plant Biology and Biodiversity Management complies with the regulations of the University and meets the accepted standards with respect to originality and quality. Signed by the Examining Committee: Advisor: Sebsebe Demissew (Prof.) Signature________________Date____________ Advisor: Tamrat Bekele (PhD) Signature________________Date____________ Advisor: Ermias Aynekulu (PhD) Signature________________Date____________ Examiner: Sileshi Gudeta (PhD) Signature________________Date____________ Examiner: Bikila Workineh (PhD) Signature________________Date____________ _________________________________________________________ Chair of the Department or Graduate Program Coordinator iii Invasion of Prosopis juliflora (Sw.) DC. and its ecological impacts in Afar National Regional State, Northeast Ethiopia Wakshum Shiferaw Gemeda Addis Ababa University, 2019 Addis Ababa, Ethiopia iv Dedicated To Afar Region Pastoral community v Invasion of Prosopis juliflora (Sw.) DC. and its ecological impacts in Afar National Regional State, Northeast Ethiopia Wakshum Shiferaw Gemeda PhD Disseratation 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. Keywords/phrases: Floristic diversity, encroachment, invasive, phenology, seed bank, soil properties vi ACKNOWLEDGMENTS I am thankful to Arba Minch University, Addis Ababa University, and GITEC project for funding different aspects of thesis. My special thanks go to my superivisors: Prof. Sebsebe Demissew, Dr. Tamrat Bekele, and Dr. Ermias Aynekulu for their unreserved guidance, valuable comments from the proposal development to the write up of the thesis. I would like to thank also Afar National Regional State Pastoral Communities Bureau for their support in writing letters of cooperation to various different and for allowing me to collect data from the varous districts. Department of Natural Resources Management in Pastoral and Agro-pastoral districts of Amibara, Awash Fentale, Teru, and Yalo are highly acknowledged for material and human resource assistance during site selection and data collection. All members of the National Herbarium of Addis Ababa University: Mr. Wage Abebe, Ms. Shewaregaw Lema, Ms. Yirgalem H/Silassie and Mr. Melaku Wondafrash are also thanked for their facilitation of material in office and the herbarium. Mr. Ali Ahimed Ibrahim and Yesuf Baba are also acknowledged for their help during data collection. I also extend my gratitude to Central Ethiopian Environmental, Forestry and Climate Change Research Center, Addis Ababa for their permission to use greenhouse for soil seed separation. I like to extend my gratitude for Mr. Habtamu Degefa of Wondo Genet College of Forestry and Natural Resources Management for his assistance in facilitating access to field equipment and encouragement during data collection. Last but not least, I extend my sincere gratitude to my family for their patience and encouragement in the course of my study. vii Table of Contents Pages ABSTRACT ................................................................................................................................... vi ACKNOWLEDGMENTS ............................................................................................................ vii Table of Contents ...................................................................................................................... viii List of Tables ................................................................................................................................ xii List of Figures ............................................................................................................................... xv LIST OF ACRONYMS .............................................................................................................. xvii 1. INTRODUCTION ...................................................................................................................... 1 1.1. Background and justification ................................................................................................... 1 1.2. Statement of problem and significance of the study ................................................................ 4 1.3. Objectives of the study............................................................................................................. 6 1.3. 1. General objectives ................................................................................................................ 6 1.3.2. Specific objectives ................................................................................................................ 6 1.4. Research questions ................................................................................................................... 7 1.5. Research hypothesis ................................................................................................................