On the crest of the eastern Andes is an expansive vista of one of the most
diverse forests on Earth. Storm clouds boil up in the pink evening sky, and fog
advances over the foothills, suffusing the mountains with the moisture that
makes them so astonishingly full of life.
These are the cloud forests of Peru. Clouds born of moisture rising from the
Amazon River Basin sustain a great variety of trees, which in turn support
ferns, mosses, bromeliads and orchids that struggle to lay down roots on any
bare patch of bark.
It's these epiphytes ("epi" means "on top of," and "phyte" means "plant"), plus
the wet humus soil, the thick understory of plants and the immersion in clouds,
that distinguish cloud forests from other types.
Miles Silman, a biologist from Wake Forest University, and other scientists are
attempting to catalog and understand the plant and animal life in Andean cloud
forests before it's too late. Oil companies, having found petroleum and natural
gas in the surrounding lands, are cutting roads and pipelines that scientists
say are damaging some plant populations. Also, local farmers and ranchers clear
cloud forest land to expand their operations and harvest firewood.
Most significant, the cloud forests here are threatened by climate change.
In other parts of the world, warmer temperatures in the past century have pushed
native species toward the geographic poles or altered their seasonal growth and
migration.
In North America, for example, the ranges of the blue-winged warbler and other
songbirds have shifted north; barn swallows and other birds are migrating
earlier in the spring than they once did; and plants are blooming sooner.
But cloud forests may be particularly vulnerable to climate change.
Of 25 biodiversity hot spots worldwide that conservation groups say deserve
special protection, the tropical Andes is the richest by far. The region has
almost twice as many plant species and four times as many endemic plants —
native species found nowhere else in the world — as the next place on the list,
the forests between central Mexico and the Panama Canal.
Many of the Andean plants have "shoestring distributions." That is, the area
where they can root, grow and reproduce stretches over hundreds of miles
horizontally — but only hundreds of feet vertically.
Says Silman to Smithsonian magazine, "I could stand upslope and throw a rock
across the elevational range of many different species."
These plants' preferred altitudes — and therefore the altitudes of the birds and
other animals that feed on them, pollinate their flowers and disperse their
seeds — are determined largely by temperature. And as the Andes heat up through
global warming, these plants may be evicted from their natural homes.
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.
Silman and Mark Bush, a paleoecologist from the Florida Institute of Technology
who studies the ancient history of these cloud forests, think that the 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.
"Plants are going to have to migrate on average 2,600 feet to remain in
equilibrium with climate," says Silman. "That's a long way, and they have to get
there by 2100." By then, according to most climate experts' predictions, the
average temperature in the cloud forest will increase by four to seven degrees
Fahrenheit.