Non-destructive methods for predicting sawn lumber properties from young, standing Eucalyptus grandis and Eucalyptus grandis X urophylla trees.
Date
2021-03
Authors
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Publisher
Stellenbosch : Stellenbosch University
Abstract
ENGLISH ABSTRACT: Eucalyptusis the most widely planted hardwood genusin South Africa cultivated for both sawn lumber and pulp. It is known for its fast growth but is prone to high growth stresses and other problematic wood properties. The properties with the highest impact on Eucalyptus sawn lumber quality are excessive board splits, severe shrinkage, brittle heart and cell collapse. This study aims to identify and evaluate methods to non-destructively test the underlying properties in standing Eucalyptus grandis and Eucalyptus grandis X urophyllatreesrelated to these lumber propertiesand to develop a predictive tool for identifying superior (plus)trees, for applications within tree breeding programmes. A secondary objective was assessing variation within and between trees for the measured properties.
70 trees, sampled from five sites close to Tzaneen, Limpopo, were split into six sample groups. Five of these groups consisted of 10 trees each, whilst the sixth group consisted of 20 trees due to the genetic variation of the trees on the site.The trees were chosen based on age and genetic improvement–two characteristics which were considered as important determinants for lumber quality. A novel paddle core system was developed for assessing growth strain within the stem of the standing tree. Additionally, non-invasive measurements of sound-wave velocity, height and diameter were taken before felling the tree. The felled trees were crosscut into two logs and four discs for further assessment. The logs were milled into boards and kiln dried for evaluating shrinkage, split length, brittle heart and collapse.The discs were processed for moisture content and density measurements.
Property analysis of the boards showed that both split length and brittle heart increased with age and decreased with radial position from the pith to bark,as well as decreased with height. Cell collapse proved to be centered around the pith, with significantly higher levels of collapse exhibited in the boards closer to the pith and little to no collapse in the boards closer to the periphery. Width and thickness shrinkage exhibited opposite trends where width shrinkage increased from pith to bark, while thickness shrinkage had a decreasing trend. Density presented a V-trend for all six groups with density decreasing just after the pith, and then increasing towards the bark. Strain measurements produced varying results between the two different tools used to mark the paddle cores.One tool indicated only compressive strain whilst the other indicated only tensile strain in the given stem. Moisture content increased with height. Time-of-Flight (ToF) of stress waves decreased with age and increased for trees that were improved through genetic selection. Cup had various radial trends for different groups and bow increased from pith to bark.
Moisture content, density, time-of-flight and growth strain were used to develop models for predicting the occurrence of the aforementioned lumber properties. It was not possible to develop models that predicted lumber properties reliably over the six age and genotype groups. The best model for predicting split length of the boards showed promise on young trees with a marginal coefficient of determination(r²) of 0.772. The input variables that can be measured on standing trees in this model were time-of-flight, moisture content and growth strain. Moisture content and strain was measured on samples obtained via limited destructive means(as measured with the paddle core method). The end split scoring system of the tree,which was used in the past to predict log quality,was also compared to the measured board splits by means of simple linear regression,but a relatively poor coefficient of determination was obtained (r² = 0.216). The newly developed paddle core method has shown potential as a predictor of growth strain.However, further improvement is still required before practical implementation can be considered.
AFRIKAANSE OPSOMMING: Raadpleeg teks vir opsomming
AFRIKAANSE OPSOMMING: Raadpleeg teks vir opsomming
Description
Thesis (MScFor)--Stellenbosch University, 2021.
Keywords
Eucalyptus grandis, UCTD, Lumber and lumbering, Time-of-flight mass spectrometry