Effects of Logging on Environmental Factors, Natural Regeneration, and Distribution of Selected Mahogany Species in Budongo Forest Reserve, Uganda
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EFFECTS OF LOGGING ON ENVIRONMENTAL FACTORS, NATURAL REGENERATION, AND DISTRIBUTION OF SELECTED MAHOGANY SPECIES IN BUDONGO FOREST RESERVE, UGANDA By JOSEPH B. BAHATI DEPARTMENT OF FOREST BIOLOGY AND ECOSYSTEMS MANAGEMENT FACULTY OF FORESTRY AND NATURE CONSERVATION MAKERERE UNIVERSITY A THESIS SUBMITTED IN CANDIDATURE FOR THE DEGREE OF DOCTOR OF PHILOSOPHY OF MAKERERE UNIVERSITY KAMPALA 2005 ABSTRACT This study explored some of the basic environmental factors that affect the natural regeneration of four mahogany species existing in the Budongo Forest Reserve, Uganda. The four species studied are: Khaya anthotheca, Entandrophragma cylindricum, E. utile and E. angolense. For each species, the biology, ecophysiology, silviculture and management are reviewed. Diverse published reports were critically reviewed and efforts made to highlight their contributions and identify knowledge gaps. Whereas forest understorey light is emphasized as the major hindrance to tropical natural forest regeneration, this study also investigated the effects of past logging in the Budongo forest reserve on soil factors and microenvironments (illumination, photosynthetically active radiation and forest temperature) and on mahogany regeneration. Three forest categories (“treatments”) including unlogged (one compartment), earlier logged (seven compartments) and later logged (three compartments) were identified from the Budongo forest main block and the two outlying forest patches (Siba and Kaniyo Pabidi). Data were collected from plots established in each compartment. A total of 258 plots were sampled. The plots were 25m x 50m each. Within each plot, mahogany seedlings, saplings and trees were sampled. From the same plots, soil samples were collected and were analyzed for texture, pH and nutrients and compared within and between treatments. Furthermore, illumination, photosynthetically active radiation (PAR) and temperature (below ground, forest floor and forest understorey-air) were evaluated to ascertain whether there were any variations in and between the three treatments. There was significant difference between the unlogged and the logged treatments (05 < P ≥ 0. 01) in terms of regeneration, edaphic and micro-environmental factors. K. anthotheca was observed to be quantitatively the most significant mahogany timber species in Budongo Forest Reserve. Next in abundance were E. cylindricum and E. angolense respectively. The least important, in terms of regeneration density was E. utile. Exploitation generally affected individuals in the larger sizes (≥ 80cm dbh). Differences in light regimes are between logged and unlogged forest tracts. The earlier and later logged treatments were quite similar, but PAR effects were detectable between the extreme forest categories (unlogged vs. later logged). Values of PAR and illumination were lowest in the unlogged forest than in the logged treatments. Contrasts between forest treatments were most marked in the later logged treatment, particularly with illumination and temperature (below ground and on the forest floor). Lower temperatures in the unlogged forest and higher temperatures in the most recently logged compartments were observed. Direct multivariate analysis of data using DCA and CCA techniques showed a significant correlation between local patterns of mahogany regeneration and some of the soil variables, available phosphorus, potassium and total nitrogen being the most important Given the significance of the role of light/PAR and temperature variations in the treatments sampled, more silvicultural effort, such as enrichment planting and conservation should be placed on compartments that were logged earlier, preferably in the 1960s. ACKNOWLEDGEMENTS This thesis is the output of a study supported by a large number of individuals and institutions. I am very grateful to all those persons and institutions for their invaluable contributions towards this achievement. I am highly and sincerely thankful to my supervisors, Associate Professor John M. Kasenene and Dr. Peter Ndemere for their professional scrutiny, constructive criticism of my reports and thesis draft and encouragement right from the inception to the completion of this study. I will be forever grateful to Dr. John B. Hall of the School of Agricultural and Forest Science, University of Wales, Bangor, who provided very useful statistical guidance during the analysis of the raw data reported in this thesis. I am very grateful to Dr. Joseph H. Obua for guiding me during the whole period of my study. I would like to say thank you to the Ford Foundation for funding the study and to Makerere University, in particular Associate Professor William Gombya-Ssembajjwe for the administration of the logistical support for this study. I am grateful to the School of Postgraduate Studies, Makerere University, for the financial assistance extended to me at the end of my fieldwork. I acknowledge with special thanks the Dean, Dr. John R. S. Kaboggoza and the Associate Dean, Associate Professor Abwoli Y. Banana, Faculty of Forestry and Nature Conservation, who encouraged me to pursue this study, to attend coursework at Indiana University, USA and to register at Makerere University. Also, I am grateful to all my colleagues in the Faculty of Forestry and Nature Conservation, Makerere University who encouraged me during difficult times. My thanks go to Professor Elinor Ostrom, Workshop in Political Theory and Policy Analysis, who supported my one year stay at Indiana University; Professor J. C. Randolph, School of Public and Environmental Affairs, who guided my interest in ecophysiology; and Associate Professor Jon Unruh and Dr. Glen Green, Centre for the Study of Institutions, Population and Environmental Change, who introduced me to GIS and Remote Sensing. Also, special thanks go to the Commissioner, Forest Department for granting me permission to study in Budongo Forest Reserve and for introducing me to Forestry Officials in Masindi and Hoima Districts. I am grateful for their cooperation and support, which made my fieldwork not only achievable, but also remarkably enjoyable. I am indebted to the co-coordinator and all technicians of the Budongo Forest Project who helped in the data collection. My sincere thanks go to Mr. Bonny Tamale and all the technicians in the Makerere University Soil Science Laboratory for the timely analyses of soil samples. Many thanks to my mother, brothers, sisters, relatives and friends for their good wishes, prayers and keeping me close to their heart. Finally, but most important, I wish to thank, with special love my wife, Grace Bahati and daughters, who all endured hardships and difficulties during my absence from home - thank you Grace, thank you my beloved daughters. Joseph B. Bahati TABLE OF CONTENTS Pag e DECLARATION ii ABSTRACT iii ACKNOWLEDGEMENTS iv TABLE OF CONTENTS v List of Tables ix List of Figures x List of Appendices x List of Abbreviations xi CHAPTER 1: General introduction 1 Summary 1 1.1 Background to the study 1 1.2 Scope of the study 3 1.3 The research problem 5 1.4 Justification of the study 7 1.5 Aim and objectives 8 1.6 Research hypotheses 9 1.7 Research assumptions 10 1.8 Thesis structure 10 CHAPTER 2: Literature review on natural regeneration in 12 closed tropical forests Summary 12 2.1 Logging and management impacts on closed moist forests in the 12 tropics 2.2 Effects of climate, forest soils, animals, forest light, temperature, 16 ground/canopy covers and crown shapes on regeneration 2.2.1 Effect of climatic factors 16 2.2.1.1 Effect of water on regeneration 17 2.2.1.2 Effects of light 17 2.2.1.3 Effect of photosynthetically active radiation 19 2.2.1.4 Effect of forest temperature on forest regeneration 20 2.2.2 Forest soils 21 2.2.3 Effect of biotic factors (animals, ground/canopy covers) 24 on regeneration 2.3 Management history of the Budongo Forest Reserve 26 2.4 Past ecological, vegetation survey and regeneration studies in 28 Budongo Forest Reserve 2.4.1 Ecological studies 28 2.4.2 Vegetation survey studies 32 Pag e 2.4.3 Regeneration studies 41 2.5 Effect of forest types on natural regeneration in Budongo Forest 47 Reserve 2.5.1 Forest types 47 2.5.2 Natural regeneration in Budongo Forest Reserve 48 2.6 Ecology of the Budongo mahoganies: state of knowledge 48 2.6.1 The Meliaceae in Budongo Forest Reserve, Uganda 50 2.6.1.1 Khaya anthotheca (Welw.) C.DC. 52 2.6.1.2 Entandrophragma cylindricum (Sprague) Sprague 55 2.6.1.3 Entandrophragma utile (Dawe and Sprague) Sprague 56 2.6.1.4 58 Entandrophragma angolense (Welw.) C.D.C. (Meliaceae) 2.7 Lessons learnt 60 CHAPTER 3: Materials and methods 62 Summary 62 3.1 Country background 62 3.2 Budongo Forest Reserve: description 64 3.2.1 Budongo forest biodiversity status 66 3.2.2 The study treatments (compartments) 68 3.2.3 Justification for compartment selection 68 3.3 Equipment used, slope correction and survey team 70 3.3.1 List of equipment 70 3.3.2 Correction for slope 70 3.3.3 The Field Team 71 3.4 Study design, selection, distribution of samples and intensity 71 3.4.1 Study design 71 3.4.2 Selection of samples 72 3.4.3 Sampling intensity 73 3.4.4 Study matrix 74 3.5 General layout of samples and data collection methods 76 3.5.1 General layout of samples 76 3.5.2 Regeneration data collection methods and procedures 77 3.5.2.1 Definitions 77 3.5.2.2 General assessment of the mahogany individuals 78 3.5.2.3 Seedling, sapling, pole, and tree measurements 79 3.6 Soil sampling layout and sample collection 80 3.6.1 Soil sampling layout 80 3.6.2 Soil samples collection