Trees that can withstand drier conditions are proliferating, while those that need more water are dying in greater numbers. The dominance of embaluba is particularly worrisome because the trees are hollow and storing far less carbon than slower-growing species like mahogany. Clearings are a natural part of the Amazonian cycle, as large trees inevitably die and other species gradually take their place. But even logging could not match the power of fire to turn the forest into Swiss cheese.
In the past half-century, 17 percent of the Amazon — an area larger than Texas — has been converted to croplands or cattle pasture. Less forest means less recycled rain, less vapor to cool the air, less of a canopy to shield against sunlight. Under drier, hotter conditions, even the lushest of Amazonian trees will shed leaves to save water, inhibiting photosynthesis — a feedback loop that is only exacerbated by global warming.
According to the Brazilian Earth system scientist Carlos Nobre, if deforestation reaches 20 to 25 percent of the original area, “flying rivers” — rain clouds that recycle the forest’s own moisture five or six times — will weaken enough that a rainforest simply will not be able to survive in most of the Amazon Basin. Instead it will collapse into scrubby savanna, possibly in a matter of decades.
Losing the Amazon, one of the most biodiverse ecosystems on Earth, would be catastrophic for the tens of thousands of species that make their home there. What scientists are most concerned about, though, is the potential for this regional, ecological tipping point to produce knock-on effects in the global climate.
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