Compression wood in conifers (Compression Wood)

Examining the formation of compression wood in conifers and its effect on timber quality

Compression wood forms on the underside of leaning and twisted stems and trunks. Its structure and chemical composition differs from normal wood, producing low quality timber with poor mechanical properties. Forest Research led this project and worked with 10 partners from across Europe in field and laboratory studies to evaluate the impact of compression wood on softwood timber and to develop solutions to minimise its detrimental effects.

Findings and recommendations

• Incidence: strong winds and snow are the biggest causes of compression wood formation as they disrupt the equilibrium position of the trees; poor rooting, unstable soils, and sloping sites exacerbate this effect
• Compression wood identification: physical or chemical examination of cell ultrastructure is most reliable, but also time consuming and expensive; use of transmitted or reflected light with rapid, semi-autonomous systems gave consistent, valid results
• Pith eccentricity: malformed pith in log ends could also help to identify compression wood in logs, but is difficult to measure in operational situations
• Shape effects: no simple correlations between tree or log shape and the occurrence of compression wood
• Log processing: careful geometric positioning of logs during sawing can reduce the presence and impact of compression wood in timber products
• Drying: specific drying schedules of timber with compression wood did not reduce distortion; compression wood should be dried and stored in the same way as normal wood

Our involvement

As co-ordinator for this project Forest Research was responsible for administrative and financial management, working with all partners to meet project milestones to complete deliverables.

Our researchers were also involved in scientific activities. We investigated the incidence of compression wood in Sitka spruce stands growing on sites with varying levels of wind exposure and slope, and in two Scots pine stands planted with different initial spacings (1.4m and 2.4m). The team analysed site soils and climate, tree competition, slope variation, and the stem shape and crown characteristics of sample trees.

The incidence of compression wood and the properties of timber were studied on two sets of sample trees felled at these sites. The team also investigated the relationship between compression wood formation and tree shape, site and climatic factors and stand characteristics.

Data collected in this project have used to model the properties of wood for Sitka spruce and Scots pine.

Funding and partners

Funded by the EU Fifth Framework Programme (75%) and the Forestry Commission (25%).

Partners:

• Forest Research (project coordinator)
• Centre for Ecology and Hydrology (CEH), UK
• University of Freiburg, Germany
• National Institute for Agricultural Research (INRA), France
• Ferdinand Braun SA, France
• University of Joensuu, Finland
• University of Florence, Italy
• Chalmers University, Sweden
• Building Research Establishment (BRE), UK