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Abstract
To understand the underlying control of patterns of important wood properties is fundamental to silvicultural control of wood quality and genetic selection. This study examines the influences of site, silviculture and seedlot on diameter growth, wood density and estimated wood stiffness in mid-rotation radiata pine (Pinus radiata D Don) stands across New Zealand. Selected treatment combinations were assessed across five sites in a 17-year-old experiment comparing silvicultural treatments and improved breeds of radiata pine. Diameter at breast height (DBH), and stress-wave velocity (an indicator of wood stiffness) and outerwood (outermost five growth rings) basic density at breast-height were assessed for ten trees from each plot in the experiment. There were large differences in DBH and wood properties between sites. Silviculture (stand density) had a stronger influence than seedlot on DBH and stress-wave velocity, while the converse applied to outerwood density. There was a positive relationship between stand density and both stress-wave velocity and outerwood density. Trees in the un-pruned 500 stems ha−1 treatment had larger DBH, lower outerwood density and lower stress-wave velocity than trees in the 400 stems ha−1 pruned treatment. This suggests that silvicultural manipulation (pruning) of green crown length is important for controlling both growth and wood properties. Results from this study support previous research which indicates that thinning, and to a lesser extent pruning, have a strong impact on DBH, stress-wave velocity and outerwood density. Increasing stand density is consistently associated with stiffer and denser outerwood.
Highlights
To understand the underlying control of patterns of important wood properties is fundamental to silvicultural control of wood quality and genetic selection
Using data from a national series of experiments, the main objective of the present study was to quantify site, silvicultural and seedlot influences on diameter growth, wood density and estimated wood stiffness in mid-rotation radiata pine stands across New Zealand
At each of the five individual sites, there was more variation in Diameter at breast height (DBH) and stress-wave velocity among silvicultural treatments than among seedlots, while the converse situation was observed for outerwood density (Figure 2)
Summary
To understand the underlying control of patterns of important wood properties is fundamental to silvicultural control of wood quality and genetic selection. Variation in wood characteristics within and between trees is affected by a number of factors including tree age (cambial ageing), environment (site and climate) and genetics (Downes and Drew 2008; Larson 1969; Zobel and Sprague 1998). Some of these factors, such as the choice of genetic material and tree spacing, can be manipulated by silviculturalists to achieve desired woodquality outcomes. From a forestmanagement perspective, the combination of using faster growing genetically improved stock and the move to shorter rotation lengths, has placed emphasis on the resultant quality of the central core of juvenile wood (Burdon et al 2004; Cown 1992; Lasserre et al 2009) as the trees grown under these conditions will have a higher proportion of juvenile wood
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