Letters

From the December 2000 issue

Bio Invaders

In "Bio Invaders" (August/September), Ronald Bailey writes that 99 percent of crop plants in the United States are non-native. I understand that the following plants were found in North America when Europeans arrived: corn, tobacco, cranberries, chestnuts, tomatoes, sweet pepper, and some yams. (Some of these are from "tropical" and Central America.) These are pretty important crops!

Bailey adds that all of our livestock, except for the turkey, are nonnative. Since the turkey is a bird, albeit generally flightless, one would normally include other birds, such as ducks and geese, which could be found in most habitable places in the 15th century. Additionally, buffalo are once again considered livestock.

Isaiah W. Cox
London, England

Ronald Bailey's open borders for "bio invaders" reads like science fiction. In keeping with the tenor of oversimplification, even if we accept the inaccurate statement that 99 percent of crop plants are nonnative, the same can be said of measles, cholera, tuberculosis, and HIV.

According to the academics Bailey quoted, the latter qualify as species "enrichment," while rejection of them is mere "religious" preference. Put another way, the benefits of cattle do not lessen the damage wrought by leafy spurge and cheatgrass. Furthermore, to compare the introduction of nonnatives via a random piece of driftwood and via a cargo boat, tens of thousands of which ply the oceans daily, asks us to believe that the quantity of insults is insignificant. That's a bit like saying that having multiple sexual partners does not alter the probability of contracting sexually transmitted disease.

Sure, case-by-case analysis would be ideal. But this assumes we can reverse unsuccessful experiments. Sadly, our few and costly successes are thus far limited to human, rather than ecological, health.

John Walker
Coaldale, CO

Ronald Bailey replies: When I said 99 percent of crop plants were nonnative, I was thinking of the bulk of food production rather than toting up individual species. The ambiguity is certainly my fault. But even looking at individual crop species, 99 percent is not far off.

First, let's agree that crops and livestock are cultivated species, not wild ones, and that the relevant region is the continental United States. Within those parameters, native crops include sunflowers, Jerusalem artichokes, and arguably cranberries, though whether they were cultivated by Native Americans is an open question. Wild chestnuts were ubiquitous in the Appalachians, but the chestnuts eaten by Americans today are generally European or Chinese. As Mr. Cox correctly notes, many of the species cultivated by Native Americans were brought from Mexico, Central America, and South America, including tomatoes, peppers, corn, beans, squash, and even some varieties of tobacco. And North America had plenty of ducks and geese, but again the domestic varieties raised today come from the Old World. Interestingly, the domestic turkey and the tomato both were brought from Mexico to Europe where they were cultivated first before being introduced to North America.

The May 2000 UNESCO Courier lists 120 crops and livestock species and their regions of origin. Only four are native to North America. Not all 120 are raised in the United States, but the fact that 96.7 percent of them come from other regions gives a rough approximation of how dependent our agriculture is on nonnative species.

Like Mr. Walker, I do not like measles, cholera, tuberculosis, and HIV. I reject them not for "religious" reasons, but because they threaten human health. In strictly biological terms, however, they do indeed count as "enriching" the biodi-versity of North America. By one estimate, 50,000 or so nonnative species now dwell in the United States, including honeybees, honeysuckle, apples, pears, pea-ches, nightcrawlers, bluegrass, alfalfa, and red clover. Most people are little bothered by their presence, and they have commingled with native species without much mischief. (Should modern American schoolchildren be taught to condemn Johnny Appleseed for heedlessly spreading invasive species?)

The point of my article is that the problem is not nonnative species per se but bad-acting nonnative species-ones that harm us economically or harm landscapes that we value for aesthetic reasons. Mr. Walker is right that increased trade among humans raises the likelihood of any given species making it to a new environment, but he misses my point that how a species arrives is immaterial-what it does in a new environment is what concerns us. I assume that Mr. Walker would favor controlling an economically damaging nonnative species even if it arrived "naturally" on a piece of driftwood.

"Ecological health" is a notoriously slippery concept. How does one measure it? Maximum productivity? Maximum number of species? Greatest stability over time? Is a tropical forest healthier than a desert, a deciduous forest more robust than a pine barrens, a virgin prairie more vigorous than a wheat farm? My point remains that a preference for native species is not a scientific issue but an aesthetic one.

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