Figure 5: Modeled (-axis) versus measured (-axis) biomass (a, c) and increment (b, d) for European forest cohorts (defined by region, species, and age). (a, b): fitting measured volume, increment and age to a single stand closure () (model A). (c, d): fitting measured volume, increment and age to one per age cohort (model B). In all fits a single productivity index () for each region and species was fitted for all age classes. Cross-validated percentage root mean squared error (PRMSE) was 37, 26, 30, and 22 for the models used in (a), (b), (c), and (d), respectively.