The fact that trees shrink by the hour during the day and grow at night could lead to researchers
being able to produce purpose-designed timber.

"We could manipulate the growing conditions of trees to produce wood suitable for fine furniture
veneer or wood for papermaking," says CSIRO's Dr Geoff Downes.

"Trees generally grow at night, and when the sun comes out they shrink," says Dr Downes. "This pattern is related to the trees' water use, with growth (i.e. tree diameter expansion) slowing and then reversing when transpiration resumes after sunrise."

Dr Downes and his team used measuring devices fixed to trees at an experimental site in Tasmania to monitor the relative position of the bark to a resolution of about one hundreth of a millimeter. 

"We were picking growth up almost at the cell level," Dr Downes says.

Using an irrigation system installed at the low-rainfall research site, the scientists were able to control the level of water stress experienced by trees, and hence find out precisely how water
availability affected growth. 

The research team has established when the growth and shrinkage phases start at different times
of the day, how long the nightly growth phase lasts, and how fast the trees grow each day.

Beginning in 1995, Dr Geoff Downes and colleagues obtained hourly readings of the growth of
blue gum (Eucalyptus globulus) and shining gum (E. nitens) trees. 

"In future we will be able to provide growers with tools which will help them to select the best
sites to grow exactly the type of tree they need to produce particular products," says Dr
Downes.

Laboratory testing has confirmed the precise correlation of stem growth rates with key wood
properties.

Dr Downes says that the number of hours during which growth occurs is less in summer than in
spring and autumn, although the rate (microns per hour) is usually higher. 

In fact, even when irrigation prevents any growth limitation due to a shortage of soil water, trees
can shrink so much during the day in summer that the night-time growth barely matches the
shrinkage. 

"Often there is no net growth over a 24 hour period in summer, even when water is available,"
Dr Downes says.

Early results show that anything that slows tree growth will lead to an increase in wood density. 

"In relating growth rate to wood density, it is not the width of the tree's annual ring that is
important but the pattern of growth over the year," he says.

Dr Downes is confident that analysis of the accumulated data will provide insights into links
between weather and soil water conditions and the development of wood characteristics that
result in costly log-end splitting. 

The research was carried out on the property of Mr David and Peter Tinning, near Hobart. It
was funded through the CRC for Hardwood Fibre and Paper Science with additional
sponsorship from Norske Skog and North Forest Products. 

Company news release
N2955