A critical analysis of methods for rapid and nondestructive determination of wood density in standing trees

Key message: Field methods for rapid determination of wood density in trees have evolved from increment borer, torsiometer, Pilodyn, and nail withdrawal into sophisticated electronic tools of resistance drilling measurement. A partial resistance drilling approach coupled with knowledge of internal tree density distribution may offer an alternative solution for wood density surveys in the future. Context: Finding ways to nondestructively assess wood density in trees has been a quest by foresters and wood scientists around the world. In the past several decades, traditional increment borer methods have gradually evolved into sophisticated electronic tools of resistance drilling measurements. Aims: We provide a comprehensive review of research development in the use of several field nondestructive methods for rapid determination of wood density in trees and discuss pros and cons of each method for field applications. Results: The use of the increment borer has been a standard method for assessing wood density in trees, and it has been further developed into a system approach allowing the use of outer wood cores and knowledge of internal density distribution for predicting wood density of major tree components. Studies on the use of torsiometer, Pilodyn, and nail withdrawal tools have had very limited success and do not warrant replacement of the increment borer. Resistance drilling, on the other hand, has emerged as a potential tool for more efficient and economical collection of wood density information in trees. Conclusion: The resistance drilling method has considerable advantages over other methods in terms of less damage to trees, faster operation, and higher measurement sensitivity. Internal friction is a key factor that currently hinders further application.