Geographer Jefferson Fox thought he was on to something big when the Chinese military stripped his team's weather monitoring equipment from a montane rubber plantation in the run-up to last year's Olympics. How big? In the past 20 years, more than 1.2 million acres (485,000 hectares) of evergreen broadleaf and secondary forests have been cleared throughout Southeast Asia to make way for rubber plantations to fuel China's growing appetite for automobile tires.

Fox—who is based at the East West Center in Honolulu—warns in Science this week that the environmental consequences of these massive land use changes, particularly on water resources, could be devastating.

Economists are also sounding the alarm, cautioning in a series of articles set to be published in Human Ecology that government policies that have forced these farmers to abandon traditional agriculture  practices will leave them vulnerable to future fluctuations in rubber prices.

Swidden, or slash-and-burn, agriculture was once practiced throughout the world as a means to cultivate on otherwise infertile soils. But with the rise of modern agricultural techniques, Europeans began to view it as an abominable and primitive practice. As Capt. P. Cupet, a member of France's Pavie Mission to Indochina in the late 19th century once wrote, "These savages are the greatest destroyers of forests I know."

But Fox and his two coauthors believe these "savages" were better at preserving biodiversity than current land-use practices encouraging monoculture, or single-crop, agricultural development in Southeast Asia. Today, Laos, Cambodia, and Thailand—with international encouragement—have adopted laws that criminalize swidden agriculture, or otherwise restrict land-use options to make the practice impossible. As a result, Fox says that Chinese investors have been able to move in and secure sometimes questionable deals that allow them to develop rubber plantations on lands once populated by leopards, monkeys and tigers.

Rob Cramb, an economist at the University of Queensland in Brisbane, Australia, agrees that the environmental fallout from the shift is striking, but he is most concerned about the livelihoods of small farmers who have been forced to change their traditional methods. He acknowledges that some may be successful in the short term, but notes that  "Having so many livelihoods tied to a single commodity (that is rubber) is potentially very dangerous."

As it turns out, Fox says that he and his colleagues were the victims of a new Chinese government policy that prevents foreigners from collecting meteorological data. Fox's research, funded by the National Science Foundation and NASA, was designed to test his theory that rubber trees, which are exotics from the South America, differ from native vegetation in that they suck up most of their water when the soil is the driest at the beginning of the monsoon season.

This phenomenon could lead to water shortages in the future, and he recommends that farmers continue to cultivate rubber but combine it with other crops and forest types. Because their experiments were cut short, he has set up new weather towers in Thailand and Cambodia to monitor how much water rubber trees absorb compared with native species.

Despite the warnings, Fox says it is unlikely the governments in Southeast Asia will change tack.

"We can report that this is not a good trend for the environment and for people's livelihoods," he says, "but I don't think it's going to stop."