SPATIAL DISPOSITION AND EXTENSION OF THE STRUCTURAL ROOT-SYSTEM OF DOUGLAS-FIR

Root systems of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) trees in The Netherlands were measured to study relationships between root system structure and size, and stem and crown diameter and growing space, all of which are relevant to tree stability. Twenty-one trees, planted between 12 and 37 years previously, were winched over and the structural portion of their root systems to a diameter of 0.5 cm and the crown perimeter were mapped. Retrospective measurements were made of the extension of major lateral roots. Size and shape of the crown projections were only poorly correlated with root system width. Reconstruction of spatial development of the root systems revealed that root spread was very limited during the first 5 years after planting. Highly significant positive correlations were found between stem diameter at 1.3 m and root biomass, and with the cross sectional area of the structural roots.