Toppling in juvenile pines: A comparison of the root system characteristics of direct-sown seedlings, and bare-root seedlings and cuttings

Abstract

Three-year radiata pine (Pinus radiata D. Don) direct-sown seedlings, bare-root seedlings and cuttings were excavated by hand from a planting trial in Taranaki, New Zealand. Eighteen trees were sampled, six of each plant type. Root system characteristics were compared by investigating differences in above- and below-ground biomass, root length, root size and root biomass distribution. No significant differences were found between plant types in total below-ground biomass, root:shoot ratio, tap root or sinker root biomass. Significant differences between plant types were found for total above-ground, branch, foliage, root bole and lateral root biomass. Additional significant differences were encountered for total root length, tap root and lateral root length. The study found the observed wind-firmness of direct-sown seedlings was unlikely to be because of the size or development of the tap root systems, the degree of symmetrical distribution of their lateral roots or higher root:shoot ratios, but could be associated with the greater proportion of total root biomass allocated to their near-stem lateral roots. It is proposed that the increase in biomass allocated to the near-stem portion of the root system, particularly on the leeward side of a tree, can be considered as an early indicator of emerging tree stability. A field-based method is suggested as a way of obtaining a measure of root anchorage. If plant types are to be developed for greater resistance to toppling, the results from this study would suggest that root stiffness, i.e. less root flexibility, should be a priority consideration in any selection or breeding programme.