i MODELING PRESENT AND FUTURE ABOVEGROUND BIOMASS OF EVERGREEN BROADLEAF FORESTS IN VIETNAM A thesis Submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Forestry by Nguyen Viet Xuan New Zealand School of Forestry University of Canterbury 2018 i ii ABSTRACT Forest reforestation and degradation have both occured over the past five decades in Vietnam. To cope with this problem, the Vietnamese government has established plans and set up strategies to reduce deforestation and forest degradation. It also launched national support for the conservation and sustainable management of forests, as well as enhancement of forest carbon stocks in developing countries (REDD+) programs. A limited number of studies have attempted to establish a database of aboveground biomass of evergreen broadleaf forests in Vietnam, as well as growth models such as height versus diameter at breast height (H-D) models, basal area (G) increment models, and above ground biomass (AGB) increment models. In addition, the information describing the relationships between environmental indicators and tree species distributions was also insufficient, leading to potential failure of reforestation and rehabilitation projects. This study examined the correlation between environmental indicators and tree species distributions. It also sought to develop H-D models based on the outcomes of grouping tree species into different groups, and model the relationship between G and AGB increments with other environment factors and stand characteristics. The study utilized data collected from Forest Inventory and Planning Insititution (FIPI) and valiation data from Vietnamese Academy of Forest Sciences (VAFS). It then employed ordination analysis to analyse the correlation between tree species groups and environmental factors. In addition, previous H-D functions applied in past research on tropical forests were used to develop H-D models for this particular study. Validation procedures were used to compare selected H-D models with other H-D iii models applied in the same forest types. Lastly, a decision tree approach was adopted to select the climatic, soil, and stand variables that were most likely to be useful for the development of G and AGB increment models. The findings were that there was a correlation between solar radiation, depth to bedrock, clay content, temperature and rainfall with tree species distributions. Nine selected H-D models for nine respective tree species groups were less biased and more precise comprared to two given H-D models in a validation procedure. Finally, both G increment models and AGB increment models were developed, in which these climatic, soil, and stand variables were directly added. The study was intended to contribute valuable data and relevant models for the benefit of forest managers and administrators who could use the results to effectively carry out the process of reforestation, REDD+ projects, and national forest inventories programs at minimal cost in timely and efficient manners. iv ACKNOWLEDGEMENTS This thesis has been completed with the support and contribution of many people and agencies. Firstly, I would like to thank my supervisory team for their great support in the completiton of my work. I am grateful to Professor Euan Mason, my principal supervisor, for his academic advice and technical support in various areas including statistics, R coding and research strategies. I deeply appreciate his patience throughout my research and writing, as well as his encouragement when I experienced difficulties during my study. I am also grateful to Professor Bruce Manley for his initial support and advice, which played a significant part in the establishment of the key research tasks of this study. In addition, I wish to express my immense gratitude to Professor Horacio Bown from the University of Chile. Professor Horacio has been one of the visiting professors at the University of Canterbury and is not formally part of my supervisor team. However, I have considerably benefitted from his knowledge and expertise, as well as his encouragement during the most critical stages in the latter part of my thesis writing. I also want to express my sincere thanks to Dr. Vu Tan Phuong for his invaluable contribution and assistance during my data collection in Vietnam. In relation, I am grateful to the Vietnam Forest Inventory and Planning Institution and various research agencies such as Silvicutural Research Institute and Research Institution for Forest Ecology and Environment of Vietnamese Academy of Forest Sciences for sharing their data, which were definitely critical in the completion of my thesis. v Most importantly, it would not have been possible for me to have this academic opportunity to undertake and complete this thesis without the financial support of the New Zealand Aid Programme of the Ministry of Foreign Affairs and Trade. Special thanks to Katinia Makaafi for her assistance throughout the most challenging times of my thesis journey. I would also want to express my gratitude to my labmates and friends, who are fellow research students at the School of Foresty. Special thanks to Serajis Salekin and Darius Phiri for their encouragement and helpful discussion on their research topics that are also related to this study. Finally, I would like to express my special thanks to my beloved wife, Van Nguyen and our two lovely daughters, Chau Anh and Khanh Chi, who provided me with love and motivation during my stay in New Zealand. I also thank my parents for their encouragement during my PHD journey. Without their kind support and understanding, this thesis would not have been possible. vi TABLE OF CONTENTS ABSTRACT ............................................................................................................ ii ACKNOWLEDGEMENTS ................................................................................. iv TABLE OF CONTENTS ..................................................................................... vi LIST OF FIGURES ............................................................................................ viii Figure .................................................................................................................... viii Short title ............................................................................................................... viii Page ....................................................................................................................... viii Figure ...................................................................................................................... ix Short title ................................................................................................................. ix Page ......................................................................................................................... ix LIST OF TABLES .................................................................................................. x Table.......................................................................................................................... x Short title ................................................................................................................... x Page ........................................................................................................................... x Table........................................................................................................................ xi Short title ................................................................................................................. xi Page ......................................................................................................................... xi LIST OF SYMBOLS AND ACRONYMS ......................................................... xii CHAPTER 1 ............................................................................................................. 1 INTRODUCTION ................................................................................................... 1 BACKGROUND ................................................................................................................................. 1 OBJECTIVES ..................................................................................................................................... 7 RESEARCH QUESTIONS ................................................................................................................. 7 HYPOTHESES ................................................................................................................................... 7 THESIS STRUCTURE ....................................................................................................................... 8 CHAPTER 2 ........................................................................................................... 10 THE EFFECTS OF ENVIROMENTAL FACTORS ON TREE SPECIES DISTRIBUTION OF BROADLEAF FORESTS IN VIETNAM ..................... 10 INTRODUCTION ............................................................................................................................. 10 MATERIALS AND METHODS ...................................................................................................... 16 RESULTS ......................................................................................................................................... 29 Species aggregation ......................................................................................................................