Adansonia Digitata L.)
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i ABUNDANCE, STRUCTURE AND USES OF BAOBAB (ADANSONIA DIGITATA L.) POPULATIONS IN OMUSATI REGION, NAMIBIA A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN BIODIVERSITY MANAGEMENT AND RESEARCH OF THE UNIVERSITY OF NAMIBIA BY FAITH MUNYEBVU 201212263 April 2015 Main Supervisor: Prof. I. Mapaure Co-supervisor: Dr. E. G. Kwembeya ii ABSTRACT This study sought to determine the biology and the uses of baobab (Adansonia digitata L.) populations in Outapi and Onesi constituencies in Omusati Region, Namibia. As one of the important Non-Timber Forest Products (NTFPs)-providing species of ecological and socio-economic significance, there is need to have a better understanding of the biology and local uses of the species before its full potential and sustainable harvesting is realized. A comparison of densities, distribution patterns, structure, phenology, stem conditions and uses of baobabs between the two constituencies was done. Field data collection was conducted in April 2014. Road transects were used to sample baobabs in the two sites by purposively choosing the next road to gain access to the next focal tree. Circular plots with a radius of 30m from the edge of the canopy of each focal tree were demarcated. In each plot, diameter at breast height (dbh) of adult and sub-adult trees, height of adults, sub- adults and saplings and their stem conditions, number of fruits on each fruiting baobab tree, the Global Positioning System (GPS) waypoints and coordinates and the land-use types where baobabs occurred were recorded. The results revealed that there was no significant difference in the baobab densities (χ2=2, df=1, p>0.05) and median fruit abundance (U=5550.5, p>0.05) between Outapi and Onesi constituencies. The Chi-square tests detected significant differences in the dbh-size classes (χ2=33.038, df=8, p<0.001) and height classes (χ2=16.295, df=4, p<0.05) between the two study sites. The bell-shaped distribution curve in dbh size-classes in the two sites showed poor recruitment. Onesi constituency had 77% damaged stems compared to 50% in Outapi constituency (χ2=22.705, df=2, p<0.001). Onesi villagers make use of the baobab tree more extensively than Outapi residents (χ2=31.022, df=9, p<0.001). Some of the common uses of baobabs in both study sites include human and livestock consumption and treating various ailments. Poor seedling survival resulting primarily from herbivory, human activities and climate variability hampers baobab recruitment. Considering the poor recruitment due to the above factors, the potential for commercialization of baobabs in the region may not be viable. Therefore, active planting in undisturbed areas, protection of seedlings from livestock coupled with community awareness are vital to ensure recruitment so that effective commercialization and subsistence use is realized and sustainable. Key words: Adansonia digitata L; baobab; commercialization; NTFPs; populations; recruitment iii TABLE OF CONTENTS ABSTRACT ............................................................................................................... ii ACKNOWLEDGEMENTS .................................................................................... vi DEDICATION ......................................................................................................... vii DECLARATION .................................................................................................... viii LIST OF ACRONYMS ............................................................................................ ix LIST OF TABLES ..................................................................................................... x LIST OF FIGURES ................................................................................................... x LIST OF APPENDICES ......................................................................................... xii CHAPTER 1: INTRODUCTION ............................................................................ 1 1.1 General Introduction .......................................................................................... 1 1.1.1 Study species .......................................................................................... 3 1.1.2 Bio-physical characteristics of baobabs ................................................. 5 1.1.3 Estimation of ages of baobabs ................................................................ 6 1.1.4 Distribution and occurrence of baobabs ................................................. 7 1.1.5 Ecological importance .......................................................................... 10 1.1.6 Baobab populations in Namibia ........................................................... 11 1.2 Statement of the problem ................................................................................. 12 1.3 Objectives ......................................................................................................... 15 1.4 Research Hypotheses ....................................................................................... 15 1.5 Significance of the study ................................................................................. 17 CHAPTER 2: LITERATURE REVIEW .............................................................. 20 2.1 Factors affecting baobab population abundance and structure ........................ 20 2.2 Influence of temperature and rainfall on baobab population structure ............ 24 2.3 Land-use and the baobab population structure ................................................ 26 2.4 Factors affecting baobab fruiting .................................................................... 28 2.5 Ecological concerns and the conservation of baobabs ..................................... 29 2.6 Baobab dietary and medicinal uses .................................................................. 31 2.7 Socio-economic values of the baobab tree and baobab products .................... 33 iv 2.8 The value chain ................................................................................................ 34 CHAPTER 3: MATERIALS AND METHODS ................................................... 38 3.1 Study area......................................................................................................... 38 3.1.1 Location and extent .............................................................................. 38 3.1.2 Climate ................................................................................................. 40 3.1.3 Geology and soils ................................................................................. 41 3.1.4 Flora ...................................................................................................... 42 3.1.5 Fauna .................................................................................................... 43 3.1.6 Socio-economic activities ..................................................................... 45 3.2 Selection of study sites and experimental design ............................................ 46 3.3 Assessment of population structure and abundance ........................................ 48 3.4 Assessment of individual plant condition and phenology ............................... 50 3.5 Socio-economic survey .................................................................................... 52 3.6 Data analyses ................................................................................................... 54 3.6.1 Population abundance and distribution ................................................ 54 3.6.2 Stem diameter frequency distribution .................................................. 55 3.6.3 Height-class distribution ....................................................................... 55 3.6.4 Stem condition ...................................................................................... 55 3.6.5 Assessment of fruit production ............................................................. 56 3.6.6 Assessments within different land-use types ........................................ 56 3.6.7 Uses of baobabs .................................................................................... 56 3.6.8 Baobab propagation and factors affecting seedlings and saplings survival ................................................................................................. 57 CHAPTER 4: RESULTS ........................................................................................ 58 4.1 Population density and spatial distribution ...................................................... 58 4.2 Comparisons of the size-class distributions ..................................................... 61 4.2.1 Comparisons between Outapi and Onesi constituencies ...................... 61 4.2.2 Comparisons of size-class distributions among land-use types ........... 62 4.3 Differences in the height structure between Outapi and Onesi........................ 64 4.4 Comparisons of stem conditions ...................................................................... 66 4.4.1 Comparisons between Outapi and Onesi constituencies ...................... 66 v 4.4.2 Stem condition and size-class distribution ........................................... 69 4.4.3 Stem condition and the land-use types ................................................. 70 4.7 Comparisons of fruit production ...................................................................... 72 4.7.1 Comparisons between Outapi and Onesi constituencies