Magnesium fertilizer, weed control and clonal effects on wood stiffness of juvenile Pinus radiata at two contrasting sites

Abstract

Two field trials established at contrasting sites (Kaingaroa and Rolleston) with different silvicultural treatments [magnesium (Mg) fertilizer or plus or minus weed control (±WC)] but identical clones of Pinus radiata were measured at age 6 for tree height (Ht), diameter at breast height (DBH) and ground-line (GLD), and modulus of elasticity (MOE) of standing trees. This study was undertaken to (i) quantify the main and interactive effects of clone, site, Mg fertilizer or WC on stem slenderness and corewood MOE of juvenile radiata pine, and (ii) examine the relationships between clonal means of corewood MOE and stem slenderness from 15 selected clones.At the Kaingaroa site, clone had a significant (P<0.001) influence on stem slenderness and corewood MOE, which exhibited a 1.5-fold variation (1.48–2.33GPa). The Mg fertilizer effect on MOE was not significant. At the Rolleston site, both WC and clone had significant (P<0.001) influence on corewood MOE. Compared to −WC, +WC reduced MOE by 7%. The MOE exhibited a 1.7-fold variation (1.67–2.83GPa) among the 15 clones. Across both sites, MOE exhibited a 1.5-fold variation (1.65–2.55GPa) among the 15 clones. Overall, clonal differences in MOE were substantial and larger than the differences due to site and WC. Significant interactions were also found between clone and Mg fertilizer, clone and WC, and clone and site.This study for the first time showed the clonal means of MOE was strongly and positively correlated to clonal means of stem slenderness. This study has the important implication for forest managers that clonal material can be closely matched to site conditions and management regimes to optimise product value.