Modelling variation in wood density within and among trees in stands of New Zealand-grown radiata pine

Abstract

Background: Density is an important wood property due to its correlation with other wood properties such as stiffness and pulp yield, as well as being central to the accounting of carbon sequestration in forests. It is influenced by site, silviculture, and genetics, and models that predict the variation in wood density within and among trees are required by forest managers so that they can develop strategies to achieve certain wood density targets. The aim of the study presented here was to develop a wood density model for radiata pine (Pinus radiata D. Don) growing in New Zealand. Methods: The model was developed using an extensive historical dataset containing wood density values from increment cores and stem discs that were obtained from almost 10,000 trees at over 300 sites. The model consists of two sub-models: (1) a sub-model for predicting the radial variation in breast-height wood density and (2) a sub-model for predicting the distribution of density vertically within the stem. Results: The radial variation in breast-height wood density was predicted as a function of either ring number or both ring number and ring width, with the latter model better accounting for the effects of stand spacing. Additional model components were also developed in order to convert from annual ring density values to a whole-disc density, predict log density from disc densities, and account for the variation in wood density among individual trees within in a stand. The model can be used to predict the density of discs or logs cut from any position within a tree and can utilise measured outerwood density values to predict the density by log height for a particular stand. It can be used in conjunction with outerwood density to predict wood density distributions by logs for stands of any specified geographic location and management regime and is designed to be able to incorporate genetic adjustments at a later stage. Conclusions: The analysis has confirmed and quantified much of the previous knowledge on the factors that affect the variation in wood density in radiata pine, particularly the influences of site factors and silviculture. It has also quantified the extent and patterns of variation in wood density within and among trees.

Modelling the variation in wood density of New Zealand-grown Douglas-fir

“…Both species exhibit strong genetic influences on wood density, and as shown in this study, the environmental effects of temperature and soil fertility are very similar for both species. Within-site variation between trees is also very similar, with the average coefficient of variation in outerwood density of 7.5% observed in this study almost identical to the value of 7.4% in a similar study on radiata pine (Kimberley et al 2015). The lack of relationship between the coefficient of variation and the mean level of density is similar to the pattern observed for radiata pine (Cown 1999).…”

“…Although both species show a tendency for wood density to increase radially from the centre of the stem, and for discs or logs to decrease in wood density with height in the stem, the effects are far more pronounced in radiata pine than Douglas-fir. Wood density typically increases by about 110 kg m −3 from rings 1 to 30 in radiata pine (Kimberley et al 2015), but only by about 65 kg m −3 between its lowest level at ring 7 to ring 30 in Douglas-fir. Disc density at 80% tree height is about 38 kg m −3 less than at the base of the stem in Douglas-fir, while in radiata pine the difference is about 70 kg m −3 (Kimberley et al 2015).…”

“…Wood density typically increases by about 110 kg m −3 from rings 1 to 30 in radiata pine (Kimberley et al 2015), but only by about 65 kg m −3 between its lowest level at ring 7 to ring 30 in Douglas-fir. Disc density at 80% tree height is about 38 kg m −3 less than at the base of the stem in Douglas-fir, while in radiata pine the difference is about 70 kg m −3 (Kimberley et al 2015). From a practical perspective, this means that the log and stem average density for a given breast density value will be higher in Douglas-fir than in radiata pine.…”

“…However, data suitable for developing such models have been collected and are described in several published studies (Cown 1999;Harris 1966;Knowles et al 2003;Lausberg 1996;Lausberg et al 1995) and numerous unpublished studies. Similar data for New Zealand-grown radiata pine (Pinus radiata D. Don) have recently been used to develop models explaining both site-level (Palmer et al 2013) and intra-stem (Kimberley et al 2015) variation in wood density, and the influence of genetic improvement (Kimberley et al 2016). Together these models have been implemented in the Forecaster growth and yield simulator (West et al 2013), enabling forest managers to analyse the effects of different combinations of site and silviculture on wood density.…”

Influence of site conditions and silvicultural practice on the wood density of Scots pine (Pinus sylvestris L.) - a case study from the Doksy locality, Czech Republic

“…It generally applies that the strength of wood increases with increasing density (Kimberley et al 2015). Wood density decreases with the increasing height of the tree, and it increases in the horizontal direction from the pith to the periphery of the trunk (Požgaj et al 1997).…”