3. Results
3.1. RelationshipsbetweenFRBdiameterclasses
We used both the FRB of trees and combined tree and under- storey FRB (total FRB) data for all the biomes to study the relationships between the root diameter classes. All the data of the FRB of trees originated from temperate and boreal forests. There were significant linear correlations between the ≤2 mm and ≤1 mm FRB and between the ≤2 mm and ≤5 mm FRB for both the trees and the trees and understorey vegetation combined (p < 0.001, Fig. 1), but there was more variation in these relationships when the tree and understorey vegetation roots were combined. The relation- ships did not differ between the needleleaf and broadleaf forests (p > 0.05).
The data standardized to the different diameter classes indicated that the standardized mean total ≤1 mm FRB for the various biomes is 25–29% smaller than the mean total ≤2 mm FRB and that of the ≤5 mm FRB 34–60% higher (Table 3). The mean total FRB biomass estimates standardized to the ≤2 mm diameter class did not differ significantly from those calculated from the original data, which contained the different diameter classes (Table 3), in any of the biomes (p > 0.05).