Standardization of fine-root definition
In order to conduct a cross-site analysis, it is essen- tial to standardize the definition of ‘fine-roots’. While a wide range of upper limits have been used, two commonly used definitions of fine-roots are diameter < 2 mm and < 5 mm (Vogt et al., 1996), which are generally well-correlated (Figure 4). We divided the entire data set into four forest categories: namely fir, pine, spruce, and broadleaf, as a compromise between the desire of deriving species specific information and