It seemed like a good idea

The world is full of things that at first seem like good ideas, but later have greater implications for the environment. Nuclear power, for example, was supposed to offer clean and renewable energy cheaply. Then came Three Mile Island and Chernobyl, and people looked at nuclear plants with less enthusiasm.

Dams looked like a smart way to manage flooding and irrigation. The Aswan High Dam in Egypt, which holds back the Nile river, was built in 1970 to allow water storage, electricity production, and irrigation. Unfortunately, the dam stopped the flow of rich silt that made the lower Nile region so fertile. Today, farmers must use fertilizer.

For more than a century in the United States, dams were routinely built to control river flooding and conserve water. In the last decade, government agencies have demolished a number of small, older dams and reopened rivers, allowing fish to resume their migrations.

In the American South, it seemed like a good idea to plant kudzu along riverbanks to stop soil erosion. In its native Japan, a pest keeps the plant in check, but here kudzu developed into an invasive weed. Likewise, in the 1920s, the US government gave cuttings of Rosa multiflora, the wild "rambler" rose, to farmers to construct natural barriers on their land. The plant grew at hyper speed, forming impenetrable thickets in pastures and on recreational land.

Like criminal casebooks, the annals of wildlife management are full of plants and animals that were innocently introduced to fix a problem, and then became renegades.

The urge to improve on nature has deep roots. But decades of mixed results have narrowed the window for experimentation and made stepping gingerly crucial.

E-mail: April Austin.