Uphill Battle

As the climate warms in the cloud forests of the Andes, plants and animals must climb to higher, cooler elevations or die.

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Scientists have described this type of forest as a nutrient-rich economy perched on a nutrient-poor substrate. The soils are acidic, cold and waterlogged. “It’s a bad place to be a root,” Silman says. As a result, he has found, most trees put on less than a millimeter of girth a year—about the thickness of a dime. That slow growth rate doesn’t portend well for the ability of cloud forests to respond to rapidly changing climatic conditions, says Silman.

We trudge down the soggy trail. At one point it opens into a wide bog covered with deep sphagnum moss. Silman takes a detour in search of a new plant, but suddenly his leg disappears into a sinkhole. He pulls it out and backtracks to firmer ground. I stay on the trail. The biologists have their binoculars out frequently, to glimpse birds flitting by. Cloud forest is so dense that most wildlife encounters are brief. Still, the scientists spot mountain-tanagers, foliage-gleaners, spinetails and antpittas. The bird population goes up as we go down. The tropical Andes harbors 1,724 species of birds—more than double the number in Canada and the United States combined.

Josh Rapp, a forest canopy biologist at Wake Forest, is one of the daredevils of our group. He uses a slingshot to shoot a small lead weight attached to fishing line over a high limb. He uses the fishing line to haul up stronger string, and the stronger string to haul up his climbing ropes. He secures the rope to a branch of the 120-foot-tall tree, dons his helmet and inches up the rope. “There’s just so much more variety, multiple layers, and varied structures up there than you get in a temperate forest,” he says. “And all this variety translates into some amazing habitats for epiphytes. There’s big tank bromeliads shooting up red stocks with multiple yellow flowers, and big clusters of pink orchids. It’s incredible.” The epiphytes may be particularly susceptible to climate change if the cloud level rises.

William Farfan, a biologist from the University of Cuzco, brings me a small orchid not much bigger than his thumb. “Look at that,” he beams. “Isn’t she beautiful?” Indeed, the tiny purple, yellow and ivory blossom is dazzling. Karina Garcia, another biologist from the University of Cuzco, demonstrates her collecting prowess with a bunch of blossoms that trail to the ground like an enormous wild bridal bouquet. The Peruvians on our expedition compete with each other to capture the rarest and most elegant treasures from the forest; so far, she’s ahead.

Collecting specimens may sound a bit old-fashioned, but paleoecologist Mark Bush of the Florida Institute of Technology, who studies the ancient history of these cloud forests, says scientists are still trying to pin down what lives here.

Work continues throughout the week. The biologists attach bands to trees to measure growth rates, collect specimens and stake out plots they will visit later to monitor changes in the forest in response to climate change. We are not without visitors. A troop of woolly monkeys swings through the canopy, hanging onto limbs that seem barely able to hold their weight, and leaping across chasms. One morning Silman spots a pair of prehensile-tailed porcupines in the canopy that he says are harder to find than jaguars in this part of the world.

Many animals here have evolved close relationships to specific types of plants. In the dense, relatively windless cloud forest, birds and insects do most of the pollinating. Sword-billed hummingbirds, with bills longer than their bodies, feed on flowers with long tubular blossoms. Sicklebill hummingbirds have shorter bills that have an almost 90 degree bend, allowing the bills to fit into similarly bent flowers of the genus Heliconia. “There are more than 200 species of hummingbirds in South America,” says Cristián Samper, director of the Smithsonian’s National Museum of Natural History, “and every one of them has a story like that.”

In previous trips, Silman and Bush have hauled in, by mule and backpack, pontoon platforms that they float on lakes in the cloud forest. They lower a hollow drill from a miniature derrick into lake bottoms to gather three-foot-long plugs of sediment. These core samples are sent to Bush’s lab in Melbourne, Florida, for analysis. The distribution of pollen in the layers of sediment offers clues to how life in the region changed in response to the last ice age.

At Lake Consuelo, near the lower limit of the cloud forest, the researchers created a sedimentary record extending back 43,000 years. Comparing their data with different sediments analyzed by other scientists, Bush and Silman believe that during the last ice age, which lasted from about 105,000 to 11,000 years ago, when temperatures fell by 9 to 16 degrees Fahrenheit in this area, species moved down from the mountains into the Amazon Basin. “Basically, the tropical forests had a much more tolerable climate for allowing species to survive,” says Bush. “The lack of enormous ice sheets moving across the land, as happened in North America, prevented the wholesale extinctions that occurred in the north.” As the earth began to warm up about 19,000 years ago, species moved back up into the Andes—but at a very slow pace.

Based on that picture of the past, Silman and Bush think that these slow-growing cloud forests may not be able to keep up with the rapid climate change predicted for this century. They and other scientists say plants won’t be able to adapt fast enough to survive in their current ranges. Trees in particular may have to move to higher elevations in just one or two generations. But no one knows whether they will flourish upslope, where the land is steeper and the soils have different chemistry, depths and microbes.


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