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Compression Wood
Compression wood in conifers - the characterisation of its formation and its relevance to timber quality

Compression wood is a type of reaction wood that forms in conifers on the underside of leaning stems, on the leeward side of trees exposed to strong winds, in crooked stems and in the lower part of trees growing on a slope. The structure and chemical composition of compression wood differ from those of normal wood. These differences result in a deterioration in mechanical properties (strength and stiffness) and increased drying distortion so compression wood can be a cause of major problems in the wood processing industry. This research will help to integrate the entire wood chain from the primary forest production to the end user. The output of the project will be advanced decision support tools in the form of predictive models linking silvicultural practice with raw material properties and end product performance.

Objectives
The overall aim of this project is to obtain a long-term improvement in the quality of European softwood timber products, in terms of mechanical properties and geometrical stability related to the occurrence of compression wood.
The main objectives of the project are:
1) to improve and standardise methods for identifying and quantifying the presence of compression wood, from the laboratory through to the industrial level
2) to increase the understanding of the way in which compression wood is formed in relation to stem form, site factors and silvicultural practices
3) to develop models and decision support tools that predict the occurrence and distribution of compression wood within individual tree stems and between trees growing under different site and silvicultural conditions
4) to develop silvicultural strategies to minimise the development of compression wood in growing trees
5) to develop industrial processing techniques to minimise the impact of compression wood on end-product performance.
The species being studied are Norway spruce, Sitka spruce, Scots pine and European larch.

Progress to Date
After 24 months, the Compression Wood project has completed the majority of work in a number of areas:
1) Almost all fieldwork has been completed.
2) Classification systems for the identification of compression wood in discs have been drawn up and initial validation completed.
3) Protocols for field, disc exchange, laboratory and industrial measurements have been drawn up and agreed by the partners.
All the measurements from the completed field sites are being compiled into a central database, which will be completed early in the final reporting period. The vast majority of samples from the field sites have been prepared and measured and are in the process of being analysed.
Detailed laboratory analysis has been undertaken of compression wood ultrastructure using the most up-to-date laboratory techniques. Preliminary analysis has also been completed on the relationship between different mechanical properties and compression wood classification. This has found that MOE tends to be lower in samples containing compression wood and that the relationship between density and MOE is weaker than in normal wood.
All saw logs have been measured and scanned. Post sawmill processing of wood containing compression wood has been conducted in planing trials and its use in window frames and re-engineered laminated timber evaluated.
Modelling work is progressing actively. Prototype models predicting the incidence and distribution of compression wood in relation to stem and log shape have been developed.

Results
1) A number of methods were developed that appear to provide reasonable identification of compression wood.
2) Attempts to establish a connection between the shape of short logs (three to four metres) and the presence of compression wood were almost universally unsuccessful. Log shape is not a good predictor on the presence of compression wood.
3) The presence of compression wood in sawn timber can lead to increased distortion and to timber with poorer mechanical performance. However, compression wood is secondary to knots, grain angle and ring curvature in determining the level of distortion and the mechanical strength of battens or in visual grading.
4) The most important factor in the formation of compression wood appears to be the climatological history of the site. Compression wood formation seems to be strongly associated with strong wind or snow events that disrupt the equilibrium of the tress.
5) The protocols developed during this project are already being used in other projects and the data gathered will be invaluable not only in continuing to answer questions concerning compression wood but also to answer other questions about wood formation and what controls wood quality.

Classified in FORESTRY, NON-FOOD PRODUCTS

Scientist responsible for the project

Professor Dr BARRY GARDINER
Forest Research, Northern Research Station
EH25 9SY Roslin, Midlothian, Scotland
United Kingdom (The) - GB

Phone: +44 131 445 2176
Fax: +44 131 445 5124
E-mail: barry.gardiner@forestry.gsi.gov.uk

References

Project ID QLRT-2000-00177
Organisation Forestry Commission Research Agency
Area 5.3.2
Start date 01 June 2001
Duration (months) 36
Total cost 3 257 960 €
Total EC contribution   1 957 664 €
Status Completed
Web address of the project   http://www.forestry.gov.uk/compressionwood

The partners

  • BUILDING RESEARCH ESTABLISHMENT LTD, United Kingdom (The) - GB
    MaunK@bre.co.uk
  • Natural Environment Research Council Centre of Ecology and Hydrology, United Kingdom (The) - GB
    ac@ceh.ac.uk
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