Secondary forests are increasing in Vietnam. Quantitative forest structure analysis is really needed. This is the basis for sustainable forest resource restoration and development in the future. This book is a small contribution to that purpose. I would like to thank Professor Sven Wagner, Chair of Silviculture, TU-Dresden, Germany. Thank you for your support to complete my research. I would like to thank my wife, sons and family for being with me and encouraging me throughout the process of doing this research.