Robert Nold's dismissal of the threat posed by non-native species is a classic case of denial (HCN, 8/3/98). By his own admission, he has "grown about 2,000 species of plants ... and few have shown any "irreversible" tendencies to invade native habitats."
Observation has shown me that "a few" is all it takes.
Since moving to central Oregon, I've seen cheatgrass, medusahead, mustard, knapweed, star thistle, Russian thistle, kochia and teasels (to name just a few non-native weeds) invade an ever-expanding acreage of range land that formerly consisted mainly of native bunchgrasses and sagebrush. Although irrigated areas may contain a greater number of these weeds than naturally dry areas, most thrive anywhere the ground has been disturbed by man or livestock.
In the nearby Ochoco National Forest, other noxious weeds doing fine without any "supplemental irrigation" are hoary cress, tansy ragwort, Dalmatian toadflax, Scotch broom, puncture vine, Saint-John's-wort, Russian and spotted knapweed, bull, Scotch and Canada thistles, Dyer's woad and burdock.
Invaders displacing native flora elsewhere in the United States include the Eurasian tamarisk, leafy spurge, kudzu vine, Australian melaleuca, and Brazilian pepper. The U.S. Department of Agriculture estimates that the United States is now home to over 4,000 non-native plants and 2,300 alien animal species, costing the country $122 billion a year.
This reduces biodiversity and causes extinctions worldwide. Here in Oregon, the latest invader is the Atlantic green crab, which, if not brought under control, will decimate the Northwest's oyster beds and destroy a $40 million annual industry. I just hope that Nold's Pollyanna nonsense hasn't won him any believers among what I trust are the more well-informed readers of this paper.