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There are a number of people to whom I owe gratitude for their assistance in the production of this thesis. Firstly I would like to thank my main supervisor, Dr Hazel Chapman, for inviting me to join her research team, and her continual encouragement, tolerance, financial support, and guidance throughout this project. Special thanks are also owed to my co-supervisor, Dr Dave Kelly, for his advise with the experimental design and statistical analyses. My appreciation is further extended to my field assistants from Yelwa village: Augustine Johnson, Misa Zubairu,and Julius for helping with the identification and measurements of trees, and Alfred Christopher, Musa Amadu, Usmanu Abubakar, and Joseph who cared for and planted out the seedlings. Finally, I am extremely grateful to my parents for their generous support and to my whole family for their encouragement during this study