Scientists putting bacteria to work in bid to save timber

Press, 14 December 1983, Page 21

Scientists putting bacteria to work in bid to save timber

DERRICK ROONEY

“Think big” may be a national catch-phrase at present, but a group of researchers at the School of Forestry at Canterbury University has been going the opposite way. They have been thinking small — with the promise of big results.

They are two-thirds of the way through a research project into a group of water-dwelling bacteria which have the unusual ability to make wood more permeable. This may not sound very exciting to the layman, but it has considerable importance to the timberpreservation industry and to foresters. If it is brought to a successful conclusion, it may well considerably widen the range of tree species which can be treated to produce ground-durable posts, and may save millions of dollars worth of roundwood which at present is left on the forest floor to rot. “Roundwood” is a forester’s term for the small logs which are removed when a partly mature forest is thinned. They are too small to be sawn for timber, but may be treated for use as posts or poles. The problem is that the number of species of tree which can be treated economically is small, and roundwood production in New Zealand is dominated by radiata pine. Roundwood production from thinnings is an important part of the management cycle of pine forests, and has both silvicultural and financial implications.

Hundreds of thousands of treated radiata posts and poles are produced each year in New Zealand, mostly for general farm fencing, a purpose for which they are quite acceptable. Pine poles are also used for deer fencing, pole houses, and other purposes. Posts with greater tensile strength are preferable for some of these uses, but radiata scores because of the ease with which it can be treated.

Douglas fir, although it has very high tensile strength, is seldom used for posts or poles, because of the difficulty and expense of treating it to make it durable. Thus while Douglas fir accounts for about 8 per cent of New Zealand’s timber production, almost no roundwood is extracted from the Douglas fir plantations. This means that the thinnings from Douglas fir plantations are left on the forest floor to rot. Foresters call this “thinning to

waste.” It is wasteful, but at present there seems to be no alternative to it.

The work being done at Canterbury University is therefore of considerable potential significance to the forest industry. If it is concluded successfully, the research may well result in major changes in the management of the Douglas fir forests. It may also greatly increase the financial return from them.

The project, which is funded by grants from the Forest Research Institute and the University Grants Committee, began two years ago, and has a year to run. The research is being done by a Ph.D. student, Mr K. Archer, under the supervision of Dr J. Walker and Dr J. D. Allen. Dr Allen has also completed a study of bacteria in beech, and is supervising a Ph.D. study of bacteria in pine logs. The School of Forestry is the only institute in New Zealand doing research into bacteria in wood.

According to Dr Walker, the implications may extend beyond the shores of New Zealand. If an economic method of treating Douglas fir can be devised, it may well be possible to modify the method to work with other problem woods, such as spruce. The impact of this on the spruce-based Northern European softwood industry would be profound. It may also be possible to apply the technique to hardwoods, such as some non-durable eucalypts, which may be grown quickly to pole size, but may be treated only with difficulty and at considerable expense.

The key to Mr Archer’s research is the capability of certain bacteria to modify.a log’s pit membranes, the microscopic “valves” which permit the flow of sap — or other liquids — between cells in the layers of wood. In radiata pine the membranes are so constructed as to allow easy passage of the chemicals used in preservative treatment, but in Douglas fir and some other timbers the membranes can jict as plugs, blocking the minute^channels between the cells. The preservatives thus cannot penetrate beyond the outer layer of wood.

Since about 1960 it has been known that certain bacteria found

in water can break up these “plugs,” opening up the channels, and the Canterbury University research is aimed at determining whether this bacterial ability can be exploited to modify the wood so that the preservatives can be distributed evenly throughout it. It is believed to be the first attempt in the world to seek a practical application for this curious bacterial appetite. A group at the Imperial College, London, is also examining the phenomenon, but is using a sapdisplacement technique, in which the bacteria are slowly sucked through the wood by applying a vacuum to one end of the log. This technique has no commercial application.

What the Canterbury researchers are looking for is a process which can be installed in a treatment plant at minimum cost, can be adapted to bulk treatment of logs, and is compatible with the commonly used tanalising method. In a sense, the project arose from the devastating nor’west windstorm which flattened most of the mature exotic forests in Canterbury on August 1, 1975. Piles of logs at Balmoral forest were stored under sprinklers to prolong their life, while a market was found for them. Subsequently, the same bacteria which had been discovered about 1960 — in log ponds in Ireland — were found in the Balmoral logs. Ironically, their presence there caused problems, because they made some of the radiata too permeable to the preservative chemicals. It occurred to the university researchers that it might be possible to use these bacteria to make denser types of wood more permeable, and thus amenable to conventional preservative treatment. This treatment, known as tanalising, applies compounds of copper, chrome, and arsenic under pressure. When these penetrate the wood they react with it, so that they become permanently “locked” in the wood.

Tanalising is not successful with Douglas fir and many hardwoods, because of the problem with the pit membranes. A Christchurch firm can treat Douglas fir and eucalypts by a different method, using bunker oil and pentachlorophenol,

but the treatment is expensive. Mr Archer collected a range of bacteria samples from Balmoral, cultured them and applied them in sprinkler tanks to sections of Douglas fir logs from Ashley forest. Some logs were incised — in a small roller mill fitted with short, knife-like spikes — to determine whether this made it easier for the bacteria to penetrate the log. Two groups — one incised and one not — were set aside as controls, and received no bacterial treatment.

When the experiment was terminated after eight weeks and the log sections were dried and treated, it was found that the logs sprinkled with bacteria absorbed

up to 350 per cent more chemicals than the control logs. While these results may seem promising, there is a long way to go before they can be put to commercial application. As Mr Archer noted in a paper on his research, the results raise more questions than they answer.

There are problems with the “relative uptake” of chemicals — in the experiment the chromium compound penetrated deeply into the wood, but the arsenic went less far and the copper even less. Further experiments will determine the role — if any — of the bacteria in this.

Further research should also indicate whether the optimum conditions have been provided for bacterial improvement of permeability. Changes in the sprinklng method, in temperature, or in timing may well cause marked changes in the results.

The research project has another year to run, and in that time some of the answers to these problems may emerge. When they do, there will still be a long way to go to a practical application for the discovery — but the university researchers will be beyond the first step towards a valuable new production technique.