"There does not seem to have been any serious field studies, in any crop, sufficient to estimate the operational effectiveness of containment genes," Strauss wrote. "Until many such studies are published, it would be unwise to assume that genes can be fully and safely contained in the near future."
Decisions to deregulate any wild GM plant like the eucalyptus must take into account this lack of research, said Hong Luo, a molecular biologist at Clemson University who has developed a gene containment system for another wild plant, turfgrass. His team recently completed a one-year study of the system's effectiveness, he said, but more research is needed.
"There haven't been really too much studies of what would be impact of transgene escape from perennials," he said. "We will be cautious in this respect."
It remains to be seen how the public will react to the concept of GM forest trees. But as researchers point out, people have already embraced some engineered trees that have no pollen controls. Almost all of the papaya trees in Hawaii are genetically engineered to resist the devastating ringspot virus, and similar efforts are under way to save the American chestnut, which has been nearly eradicated by fungal disease.
However, the inability to promise 100 percent containment could delay the development of bioengineered plants that carry even slight risks of invasiveness. But such foolproof systems will come, Strauss predicted.
"I do believe we can produce absolute containment," he said. "We will be able to do that, I believe, in 10 years. But it's not proven yet."
The unproven nature of ArborGen's fertility controls is concerning largely because they will be used to introduce a robust, foreign tree, conservation groups say. The timber industry has long dreamed of importing eucalyptus into the South, mimicking Brazil's success, where plantations transformed the country -- at some environmental toll -- from a timber importer to an exporter within decades.
Previous domestic efforts to establish the tree in the South, which came to a peak in the early 1980s, failed as winter freezes scythed dead swaths through experimental plantations. Only in Florida have the trees survived, though they have only been used in only limited ways, mostly for mulch. All efforts to move the tree into more temperate conditions have failed, until now.
Thanks to a plant gene that it licensed from Mendel Biotechnology, a prime R&D contractor with Monsanto Co., ArborGen's freeze-tolerant eucalyptuses have been grown in much colder conditions up into the Carolinas. (ArborGen has many connections to Monsanto, starting with its CEO, Barbara Wells, who worked at the seed giant for 18 years.) Mendel's regulatory gene controls the expression of other genes that influence cold resistance, and its use represents the state of the art in plant biotech.
But in opening the door to the plant's cultivation, far more scrutiny is needed as to how eucalyptus will behave when grown in bulk, said Doria Gordon, a senior ecologist at the Nature Conservancy.
"My concern is about invasiveness. Not that it is a GMO, per se," Gordon said. "The concern is, what threat is it to Florida's natural area and to the Southeast's natural areas?"
Last year, Gordon, who also works at the University of Florida, evaluated one of the two species used to breed ArborGen's hybrids, Eucalyptus grandis, also known as the rose gum. The tree had previously turned invasive in South Africa, Gordon found, which led her to conclude that the tree carried a risk of turning invasive in the South, as well.
Gordon serves on a panel that evaluates the invasive risk of plants in Florida, and last year, the panel classified the rose gum as a possible invader. Only a few variants of the tree can be grown, it said, and only with strict management practices, including harvesting within six months of the onset of flower production -- much sooner than a forest plantation would like.