Early root development of field-grown poplar: effects of planting material and genotype

BACKGROUND: Poplar trees (Populus spp.) are used widely for soil conservation. A key advantage is their ability to establish from unrooted stem sections of varying dimensions, ranging from small cuttings to large poles. This study determined root length and biomass of young trees from three different-sized stem sections and quantified clonal variation. METHODS: Two concurrent field trials were conducted: trial 1 compared root attributes of trees from cuttings, stakes, and poles of a single poplar clone, while trial 2 compared those of trees from cuttings of six poplar clones. Excavations of entire trees were conducted in autumn for three (trial 1) or two (trial 2) years after planting. RESULTS: Total root mass averaged over 3 years was in the order poles (364 g) > stakes (70 g) > cuttings (17 g), and total root length was in the order poles (73 m) > stakes (21 m) > cuttings (7 m). Maximum lateral root extension was approximately 2.6 m from poles, 1.7 m from stakes, and 0.8 m from cuttings. Clonal variation in trees from cuttings was found for both mean total root mass (10.4–45.9 g) and total root length (3.5–11.8 m). In both trials, root mass and length increased, decreased, or were unchanged with increasing 0.5-m increments of the distance from stem and soil depth, depending on year, planting material, root diameter, and their interaction. CONCLUSIONS: Early root development from poles was greater than from cuttings, with development from stakes being intermediate. Different poplar clones exhibited large variation in root biomass development within 2 years of planting. The results provide an understanding of the differences in early root development of poplar planting materials and clones used for soil conservation and other purposes and guidance on appropriate tree spacings of different planting materials to achieve root interlock.