FAO has predicted that worldwide wood demand will have increased by 25 percent between 1996 and 2010. This increase won’t be met from natural forests – 35 percent of the world’s industrial wood comes from plantations, although they made up only 5 percent of total forest cover in 2000.

Plantation area will grow to meet demand. Globally, it increased fourfold between 1990 and 2000, and that trend is expected to continue, especially in developing countries. Where will the land come from?

“It is impossible to ignore any sound strategy for making plantations more productive,” says FAO forest geneticist Pierre Sigaud. “Such strategies might include genetically modified trees. But they also include better seed selection and management practices.”

And where genetic improvement is needed, he points out, there is far more untapped potential in existing forest genetic resources than in agriculture -- where the crops have largely been domesticated and there are fewer wild relatives on which to draw for breeding purposes. So GMOs could have a role – but their use would be limited to plantation forestry, while, globally, the majority of forests will remain natural forests.

Longer life cycles may mean more instability

The longer an organism grows, the greater the opportunity for variations in its environment. As a result, genetically modified trees present unique challenges. The long life of a tree means that it is more likely to encounter stresses – such as weather and pests – that could trigger unpredictable genetic responses. The slower growth of trees means that problems will take longer to show.

One risk is related to the spread of modified genes into natural populations, as tree pollen disperses widely. On the other hand, plantations often rely on introduced species that have no wild relatives growing nearby – limiting the opportunities for crossing with wild populations.

But the differences between trees and crops cut both ways. “With crops, you can adapt the environment to the plant with agronomy and agrochemicals,” says Dr Sigaud. “But forests take years or decades to mature, and such practices are often uneconomic and in any case are often regulated. So a tree has to be suitable for its environment, whether it’s genetically modified or not. There are few species for which genetic modification can bring significant advantages compared to traditional selection and improvement programmes.

In any case, commercial constraints limit opportunities for genetic modification of trees. Growing and harvesting a plantation takes time and money, as do trials. Because of this and concerns over public opinion, genetically modified trees so far have not been planted commercially, although there has been plenty of research – especially in high-yield plantation species.

Opportunities and dangers

Besides faster growth, qualities anticipated from genetically modified trees include: better tree form; more uniform wood quality; lower or modified lignin content; pest resistance; herbicide tolerance; sterility; and adaptation for harsh environments.

If genetically altered trees are released commercially, the first modifications are likely to be for modified lignin content, pest resistance and herbicide tolerance.

  • Lignin is a heavy tissue that gives strength to plant cell walls and helps support the tree. Breaking it down during pulp and paper production requires costly, environmentally hazardous chemicals. Trees with reduced lignin could be processed more cheaply and cleanly. But they may have less resistance to pests and high winds.

  • Pest resistance has already been bred into commercially released genetically modified food crops. It causes them to produce toxins that kill pests and then degrade quickly in the environment, thus causing limited direct harm to the environment. The same technique could work for trees, although there are concerns that their long life cycle could give pests more chance to develop resistance to the toxins.

  • Herbicide tolerance could permit more targeted application of herbicide, thus reducing the amounts used. But this application is less important than with crops -- in forestry, herbicides are generally used sparingly and only when a forest is being established.

Further ahead, there could be more environmentally friendly applications. Trees can prevent or reverse land degradation, and tree improvement, whether by genetic modification or not, could bring new opportunities of this type. Trees bred for harsh environments could help protect fragile land on desert margins, while those bred for salt tolerance could help restore the productivity of land damaged by poor irrigation practices. Also, faster-growing trees – in addition to their commercial possibilities – could help fight global warming by taking more carbon dioxide from the atmosphere and converting it into plant matter – a process called carbon sequestration.

A safe technology?

While wood is not consumed by humans, other parts of forest trees do get into the food chain, through the consumption of pollen, honey, wild fruit and game, for example. Long-term environmental risks may be more easily overlooked, especially as forest plantations may be remote and not closely supervised. In any case, all newly introduced ‘natural’ or improved tree species need careful supervision, independently from genetic modification.

Making GMO trees sterile so they do not breed and release genetically modified material into the environment is an important safeguard, but it may not be completely reliable. Trees without reproductive features might reduce the diversity of birds and insects that feed on them. These questions call for caution, as should the cost and effort of investing in such technology and the time needed to get that investment back.

A further disincentive to genetic modification in forestry is the wide, largely unexplored diversity of existing forest species. Much of this can be used to make forests and forest plantations more productive, using traditional tree improvement and breeding techniques combined with sound silvicultural practices.

Commercialization of genetically modified trees could come and may make trees even more useful in a number of ways. But the technology is not likely to be adopted as quickly or as broadly as in other sectors.

March 2003