prompted applications of insecticides. Many of these new traits for improving agricultural production on farm are ones that could have environmental impacts that are similar in kind to the present generation of transgenic crops. Their value accrues directly to the farmer and the seed company and only indirectly to other sectors of society. Their potential risks, however, are borne by a wider segment of society. Thus, risk analysis of this next generation of traits is likely to resemble present discussions and debates about biotechnology. The evaluation of these risks is likely to become more complicated and difficult as the range of transgenic crops expands from the major grain crops to the more wild and perennial plants, such as pines and poplar.
Over the long term, new knowledge regarding the physiology and development of plants and their interaction with microorganisms could eventually provide the foundation to modify plant structure and reproduction. It may become possible to genetically engineer crop plants that are more tolerant to drought, salinity, and other abiotic stresses (see below); that are able to grow more efficiently in the acidic, aluminum-containing soils found in tropical areas (Herrera-Estrella 1999); that can compete more effectively with weeds; that can reproduce in a shorter time; and that can potentially fix their own nitrogen.
Transgenic technology is also being applied to several commercially important tree species, including poplar, eucalyptus, aspen, sweet gum, white spruce, walnut, and apple (Kais 2001). The global demand for wood and wood products is growing along with the human population. To reduce pressure on existing forests, forest plantations that grow transgenic trees are expected to play an increasingly important role in meeting the demand for tree products (Tzfira et al. 1998). As mentioned above, the first traits being genetically engineered into trees are herbicide tolerance and insect resistance, which are useful for establishing and maintaining young trees. Several traits are under development to better adapt trees to postharvest processing, and these may become commercially available in the near future. For example, there is research under way to modify the lignin content of certain tree species, in order to improve pulping, the process by which wood fibers are separated to make paper. Reduced lignin may improve the efficiency of paper production and may reduce environmental pollution from the paper production process.
To restrict the transfer of transgenic traits to wild forest and orchard tree populations, it is generally considered essential to simultaneously genetically engineer reproductive sterility. Methods currently exist to do this in crop plants (Mariani et al. 1992, Williams 1995), so this technology