Tree improvement and sustainable forestry - impact of two cycles of loblolly pine breeding in the U.S.A.

The N.C. State University-Industry Cooperative Tree Improvement Program has completed 43 years of genetic improvement for loblolly pine in the southern U.S. The impact of the tree improvement on forest productivity has been substantial through the two cycles of breeding, testing and selection. The southern U.S. plants more than one billion loblolly pine seedlings annually, all of which are genetically improved seedlings from seed orchards. Trees grown from seeds of first-generation seed orchards have produced 7-12% more volume per acre at harvest than trees grown from wild seed. Second-generation seed orchards are now producing more than 50% of the total seed harvest in the region with estimated gains ranging from 13% to 21% in rotation volume over unimproved seedlots. When second-generation seed orchards are rogued to the best 30% of the parents, gains of 26% to 35% in volume production at harvest should result. Gains over the first-generation are estimated to be 14 to 23% additional for rogued seed orchards. Genetically improved stock has not only demonstrated outstanding growth, but has also lower infection from fusiform rust, typically 20-25% below the unimproved seedlots. With additional improvements in value from quality traits (stem straightness and wood quality), the estimated genetic gains in value should be much greater. The intensively managed plantations of loblolly pine with genetically improved materials have had and will have significant impact on the sustained management of forest resources in the southern U.S. Although only 15 percent of the commercial forests are currently in plantations (11 million hectares), almost 50 percent of the South's timber supply will soon come from them. Improved wood production on limited commercial lands will reduce the logging pressures on natural forests, old-growth and ecologically sensitive forests. By increasing wood production per hectare in plantations, rather than by managing more hectares of forest, genetics, in combination with intensive silviculture, can and will provide better opportunities for the use of natural forests and forest lands for conservation and recreational purposes. Results from two-cycles of loblolly pine breeding strongly suggest that high-yield plantations by genetic improvement can contribute significantly to the conservation and sustained use of forest resources. The future impact will be even more dramatic as the tree improvement program moves to advanced generations. Together with intensive silvicultural practices, forest genetics and tree improvement will continue to contribute significantly to the sustained management of world forest resources