A Luoi Valley, Vietnam: When Phung Tuu Boi began working here in 1975, he found an ecosystem devastated by war. Aerial spraying of defoliants like Agent Orange had destroyed large swaths of forest. Without live roots to anchor the soil, monsoon rains washed away the topsoil and its nutrients, allowing invasive grasses to take over and prevent forest regeneration.

A botanist by training, Boi initially intended to reforest the denuded land. But he soon realized that the forest ecosystem was not the only thing struggling to recover from Agent Orange.

Boi has used the humble acacia tree to reforest thousands of hectares in central Vietnam. Emboldened by these successes, he has applied his botanical model of remediation to tackle a far more difficult problem.

There are hot spots like the former A So air base in Dong Son, where scientists from Hatfield Consultants in Vancouver, British Columbia, have measured soil levels of TCDD, the dioxin in Agent Orange, more than 200 times greater than the residential standard set forth by the U.S. Environmental Protection Agency.

Dioxin takes decades to break down. Remediating this site would require millions of dollars, and when it comes to financing, the more heavily populated hot spots in Danang and Bien Hoa take precedence.

Boi has developed a low-tech method to keep people from using what looks like arable land. The chemical that taints this soil cannot be seen, smelled or tasted. He builds a green fence, thorny, soft wood not useful as firewood.

The trees he has chosen to make up the fence, Gleditschia australis, produce a fruit that residents can sell to make soaps and medicinals. Gleditschia, a type of honey locust, is disease and insect-resistant, and its thorns and soft wood should deter residents from cutting it down for firewood.

The Vietnamese people are steadily overcoming decades of colonial war with France and the United States. They usually rely on low-tech solutions to the long-term effects of those wars. That’s all they can afford.

It’s been a long time since the United States did anything about cleaning up after a war.