1493_ Uncovering the New World Columbus Created - Charles C. Mann [157]
THE END OF THE WORLD
The morning had been clear and bright, an ominous sign. On the pedestrian bridge that leads to the Xishuangbanna Tropical Botanical Garden I could see the faintest skirl of fog on the hills. Researchers had drawn their office curtains on the building’s sunny side. Founded in 1959, the garden grew up with Xishuangbanna’s rubber industry. Its scores of scientists monitored the impact of the refashioning of the regional ecosystem and didn’t like what they saw. “We all hate rubber,” one researcher told me. “But then we’re all ecologists here.”
Although the Golden Triangle receives as much as one hundred inches of rain a year, three-quarters of it falls between May and October. The rest of the year the forest survives largely on dew from morning fog. “Back in the 1980s and 1990s there was still fog at lunchtime,” XTBG ecologist Tang Jianwei told me. “Now it’s gone by eleven.” The “very obvious” change, he said, is a symptom of a profoundly altered hydrological regime.
Rubber is to blame, Tang said. H. brasiliensis usually sheds its leaves in January and new leaves begin budding in late March. The absence of leaves means that the forest has fewer surfaces to retain dew, which reduces water absorption during the dry season. Surface runoff rises by a factor of three—which in turn jacks up soil erosion by a remarkable factor of forty-five. Worse, the new leaves’ most intense growth occurs in April, at the dry season’s hottest, driest point. To propel growth, the roots suck up water from three to six feet below the surface. Tapping begins as the new leaves appear and continues until they fall. To replace the lost latex, the roots suck up still more water from the ground. How much water? Tang did some rough estimates with pen and paper. Half a kilogram of latex a day, twenty days a month tapping, 180 trees to the acre … good latex is 60 to 70 percent water … 4,400 pounds of water a year per acre. Rubber producers are effectively putting all the water in the hills into trucks and driving it away. “A lot of smaller streams are drying up,” he said. “Villages have had to move because there’s no drinking water.” Now spread this impact across Laos and Thailand, he said. It would be a slow-motion remaking of a huge area. “It’s not easy to tell what the effects would be,” Tang said.
Beginning to heed ecologists’ worries, Xishuangbanna effectively banned new rubber planting in 2006 by freezing all land rotation. The scheme is unlikely to have much effect. To begin with, as Shi notes, it seems to violate China’s newly reformed land laws. But even if Xishuangbanna farmers were to stop planting H. brasiliensis tomorrow, its area would keep rising—on their own, rubber trees are invading the remaining forest.
Almost every bit of Xishuangbanna that can support rubber trees has been cleared and planted (top), a change that is profoundly altering the environment—the region’s morning mists are vanishing, along with its water supply. With China’s rubber companies running out of suitable land in China itself, they have moved across the border to northern Laos (above, a freshly logged hillside). (Photo credit 7.8)
Hillside rubber plantations surround Tang’s office in the botanical garden. Because trees are grafted from the wood of high-yielding specimens, the great majority of the rubber trees in Southeast Asia are clones. And the majority of the trees used to create those clones descended from the few sprouts that survived from Henry Wickham’s original expedition—a slice of a slice of a slice. These are the trees that Weir brought to Fordlândia, the varieties so highly susceptible to M. ulei. The trees make a canopy of green so unbroken that Beijing legally describes rubber plantations as “forests”; locals can fill fallow farmland with rubber and fulfill government conservation dictates. As