In the News

Unit 6: Interactions and Interdependence

In the News

Climate Change and the Rain Forest: Adaptations and Predictions

A large-scale, innovative experiment in the Amazon rain forest is leading to surprising predictions about the effects of climate change.

Global warming, future El Niños, and increased global logging and farming will likely lead, many scientists think, to a drier future, particularly for rain forests. The experiment is an attempt to see into that future.

For almost five years, scientists diverted rainfall from a 2.2-acre section of the rain forest in western Brazil to see what would happen to the plants. During the wet season, they used a complex series of plastic panels, similar to a greenhouse, to shield the ground and plants from rainfall. During the dry season, they removed the panels. They used a nearby rain forest section as a control area.

After five years of greatly reduced moisture, most of the smaller trees and other vegetation were still standing. However, after the first year, many of the trees stopped growing. Additionally, they closed down their stomata to reduce water loss through the openings. This led to a decrease in photosynthetic activity and a reduction in the amount of carbon removed from the air. Surprisingly, the trees did not drop large numbers of leaves, as scientists had expected. Rather, wood production slowed as photosynthesis slowed and tree diameter did not change.

To survive, the plant life had to get water from somewhere. But where? Scientists found that the normally shallow-rooted rain forest trees sent their roots deeper into the ground in search of moisture. By the end of the observation period, some trees had sent roots down 40 feet and more.

Scientists were surprised that many of the smaller trees proved to be highly adaptable to the new, drier conditions. The older, larger trees did not fare as well. Trees 130- to 150-feet tall eventually began to die as deep soil water reserves dried out. If that trend was allowed to continue, the death of the large trees would have led to a shorter and more open forest.

Over the next two years, scientists will continue to study their 2.2-acre plot as they allow normal rainfall conditions to return. They are interested to see if and how the rain forest recovers from the artificial drought. This might help them learn how rain forests respond to temporary droughts, such as those that occur in El Niños. Unfortunately, it is unlikely to help them understand the long-term effects of global warming and deforestation.

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