19 September 2006
A portable instrument to predict wood properties directly from standing trees in the forest could provide an effective way to assess wood quality for Australia’s expanding woodchip export industry, according to a new FWPRDC study.
The application of the near infrared (NIR) spectroscopic instrument is a response to industry demand for an efficient way to predict characteristics such as Kraft Pulp Yield (KPY) from samples taken from standing trees.
According to Ensis principal investigator Dr Geoff Downes, the system provides a rapid in-field analysis of drill-core samples and presents “substantial opportunities for commercial development and use in field-based studies”.
NIR is widely used for non-destructive quality assessment of agricultural products and its use to predict wood properties has been proven but there has not been a shift to routine commercial use because the technology’s consistency and accuracy has not been robustly demonstrated.
However, Dr Downes said the study results indicated that NIR spectra obtained in the field from either standing trees or samples taken from standing trees could be used to accurately predict KPY in a fraction of the time and cost of traditional methods. Conventional analysis of KPY requires destructive sampling and costly laboratory-based investigation which prohibits routine assessments of forest value.
“NIR calibrations based on spectra measured from green wood samples provided good predictions of whole-tree KPY and reasonable predictions of basic density,” he said. “They showed that a portable NIR could estimate the KPY of a standing tree to within one per cent of its true value 70 per cent of the time using field-collected spectra.”
Dr Downes cited pulp yield as a key factor in the economics of tree growing for paper production and tree growers have been breeding for this property for many years.
“NIR is an efficient way to assess young trees for this characteristic,” he said. “Pulp yield varies with the alkali-resistant starch content of the wood and NIR is suitable for detecting this chemical variation.”
Spectra from bark-free surfaces of standing trees and chainsaw frit proved useful as they were easy to obtain. However, it is necessary to explore the effects of seasonal variation on calibration models because spectra from bark-free windows represent only the outer millimetre of wood.
“Spectra obtained from either the hole left during coring or the core itself provide the greatest potential for using NIR to assess radial patterns of KPY and density variation in stems,” Dr Downes said.
The new Ensis Global KPY prediction model developed over the past two years was also tested to gauge the extent to which a single generic calibration could be used to predict KPY in eucalypts across various sites and age classes – a process Dr Downes described as “essential if NIR is going to shift to routine commercial use”. The model delivered reasonable KPY predictions in 45 trees investigated.
The portable field-based NIR instrument will undergo a cost-benefit analysis to measure its value against laboratory examination of wood samples. If deemed valuable, a validation study will be conducted to develop the technology into a standard analytical or inventory method.
This release can be viewed on the FWPRDC website: www.fwprdc.org.au
FWPRDC
Dr Glen Kile, Executive Director
T: (03) 9614 7544 Ensis
Dr Geoff Downes
T: (03) 6226 7962
Wood residue resulting from tree coring was collected and NIR spectra obtained from it.
Standing tree acoustic measurements were used to explore relationships between pulp yield and standing tree stiffness.