Abstract
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. 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. 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. 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.
Highlights
Poplar trees (Populus spp.) are used widely for soil conservation
Shoot diameter of planting material (PM) was similar in year 1 (Y1) whereas, in year 3 (Y3), the diameter of poles (66 mm) was 16 % greater than from stakes (57 mm) and 113 % greater than from cuttings (31 mm)
Veronese is grown for a range of applications (National Poplar and Willow Users Group 2007), but this study found that its early growth from cuttings was less than Kawa for shoot length and shoot mass and less than Kawa and Geyles for total root mass
Summary
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. Species and hybrids of the genus Populus (poplar) are important examples of trees used in erosion control and remediation programmes in many regions of the world (Wu et al 1994; Lammeranner et al 2005; Licht and Isebrands 2005; Reisner et al 2007; Blanco and Lal 2008). The advantages of using poplar for erosion control include rapid growth, high evapotranspiration rates, extensive lateral root systems, abundant fine root production, and rapid tree establishment from vegetative material. Fewer belowground investigations have been conducted recently (Benomar et al 2013; Berhongaray et al 2013; Hajek et al 2014; Phillips et al 2014), and this imbalance needs addressing because root characteristics and their spatial and temporal changes are important in determining efficacy for soil stabilisation (Stokes et al 2009). There is limited knowledge of the genetic variation in root attributes of populations of poplar which hinders identifying the most appropriate clones for stabilising soil
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