Root CSA-Root biomass prediction models in six tree species and improvement of models by inclusion of root architectural parameters

Models were developed for Norway spruce, Sitka spruce, Scots pine, Pedunculate Oak and European Beech to predict the biomass of individual structural roots based on either basal root cross sectional area (rCSA) assessments ( basic models) or on rCSA and additional root architectural measurements (multiple models). The material embraces 1257 roots from 337 trees derived from 33 stands. The soil types of the investigation cover sandy podzols, sandy moraine, brown earth, deep peat, and pseudogley, but all species were not represented on all soil types. The models were developed for stands in three dimension classes depending on the average diameter of the stands and for horizontal roots (angle to the surface less than 45 degrees) and vertical roots (angle to the surface greater than or equal to 45 degrees), respectively. Simple models using rCSA near the stump to predict coarse root biomass (logarithmic models) did not account for stand differences in Norway spruce and Sitka spruce. To eliminate these differences, it was necessary to include root taper and vertical root parameters in the models. Variation between stands concerning the regression between rCSA and root biomass was not found for Pedunculate Oak, Scots Pine or European Beech, but the number of stands of these species was also limited compared with Norway spruce and Sitka spruce.