Abstract
Root biomass can represent a significant proportion of the total ecosystem biomass, although the difficulty in extracting the roots is often a limiting factor when estimating the belowground biomass. The objective of this study is to create equations to estimate the root variables from other tree variables for mizunara oak (Quercus crispula BLUME) in broad-leaved secondary forests. First, experimental plots were established in secondary forests dominated by mizunara oak and sample oak trees were felled just outside the plots. The biomass of each tree organ was measured and other root variables such as root length, area and volume were also measured. Then, allocation of the four root variables by root diameter classes was described. Regression equations by power function were created between the four root variables and root diameter to estimate the missing root parts by root diameter classes and for the total root system. Root variables for missing parts were estimated from the diameter of broken root ends with regression equations between the four root variables and root diameter for total root system. Finally, allometric regressions between root variables and other tree variables were analyzed both by root diameter classes and for the total root system. Diameter at beast height (DBH) proved to be a good predictor of root variables for different root classes and for the total root system. Diameter at stump height (DSH) can be a useful estimator if branching starts at DBH as it also shows high correlation with root systems.
