Modelling the influence of environment and stand characteristics on basic density and modulus of elasticity for young Pinus radiata and Cupressus lusitanica

Abstract

Data taken from 261 4-year-old trees growing within a nationwide set of site quality plots where Pinus radiata D. Don and Cupressus lusitanica Mill. were established at high stand densities (40,000 stems ha −1) were analysed to (i) determine how site, species and fertilisation influence the wood properties basic density and green dynamic modulus of elasticity (MOE) for the stem at the tree base, and (ii) develop predictive models of basic density and MOE for both species. A further objective was to examine the utility of the “experimentation in miniature” (EIM) approach used here, to identify key determinants of wood properties across an environmental gradient. Site mean variation for both wood properties was highly significant with treatment-averaged values ranging from 27% (365 to 465 kg m −3) for density to twofold for MOE (2.4–5.9 GPa). Basic density of C. lusitanica significantly exceeded that of P. radiata by 12% (457 versus 407 kg m −3), while MOE of P. radiata significantly exceeded that of C. lusitanica by 33% (4.4 versus 3.3 GPa). Neither fertilisation nor the interaction of fertilisation and species had a significant effect on either basic density or MOE. Although key determinants of basic density were very different between species, they exhibited considerable similarity for MOE. In the final multiple regression model of basic density for C. lusitanica ground-line diameter accounted for 88% of the variance, while for P. radiata 90% of the variance in basic density was explained by total soil phosphorus (P), average leaf area index (LAI), total annual radiation, and average minimum air temperature during winter. The final multiple regression model of MOE for C. lusitanica accounted for 90% of the variance using stem slenderness, average air temperature during winter, and average LAI, while stem slenderness and total soil P accounted for 96% of the variance in P. radiata MOE. Key determinants of P. radiata basic density previously identified across an environmental gradient at conventional stockings were consistent with our results. Results from our study also demonstrate that previously unmeasured variables, within these conventionally stocked stands, such as total soil P and LAI may also have an important influence on P. radiata basic density. Although preliminary and limited to a single wood property in P. radiata this comparison suggests that EIM has some utility for identifying key determinants of wood quality across environmental gradients.