Chile's Fray Jorge National Park
Image courtesy of Juan J. Armesto/Foundation Senda Darwin Archive
On the rugged roadway approaching Fray Jorge National Park in north-central Chile, you are surrounded by desert. This area receives less than six inches of rain a year, and the dry terrain is more suggestive of the badlands of the American Southwest than of the lush landscapes of the Amazon. Yet as the road climbs, there is an improbable shift. Perched atop the coastal mountains here, some 1,500 to 2,000 feet above the level of the nearby Pacific Ocean, are patches of vibrant rain forest covering up to 30 acres apiece. Trees stretch as much as 100 feet into the sky, with ferns, mosses, and bromeliads adorning their canopies. Then comes a second twist: As you leave your car and follow a rising path from the shrub into the forest, it suddenly starts to rain. This is not rain from clouds in the sky above, but fog dripping from the tree canopy. These trees are so efficient at snatching moisture out of the air that the fog provides them with three-quarters of all the water they need.
Understanding these pocket rain forests and how they sustain themselves in the middle of a rugged desert has become the life’s work of a small cadre of scientists who are only now beginning to fully appreciate Fray Jorge’s third and deepest surprise: The trees that grow here do more than just drink the fog. They eat it too.
Fray Jorge lies at the north end of a vast rain forest belt that stretches southward some 600 miles to the tip of Chile. In the more southerly regions of this zone, the forest is wetter, thicker, and more contiguous, but it still depends on fog to survive dry summer conditions. Kathleen C. Weathers, an ecosystem scientist at the Cary Institute of Ecosystem Studies in Millbrook, New York, has been studying the effects of fog on forest ecosystems for 25 years, and she still cannot quite believe how it works. “One step inside a fog forest and it’s clear that you’ve entered a remarkable ecosystem,” she says. “The ways in which trees, leaves, mosses, and bromeliads have adapted to harvest tiny droplets of water that hang in the atmosphere is unparalleled.”
Every living thing here does its part. Mosses and lichens absorb moisture from the air like sponges. Tree leaves are oriented to provide the broadest surface to the incoming fog rather than to the sun. Dead leaves collect in the crooks of branches, creating little pockets of soil in which ferns, mosses, and bromeliads grow. Trees sprout roots that extend into these masses of lodgers to extract their share of the moisture. Birds, beetles, and other creatures in search of water migrate into the forests during the dry summers. Birds and bats then spread the seeds and pollen of these remarkable plants.
Even more marvelous is the way the trees at Fray Jorge receive nutrients as well as water from the fog. Weathers and her colleagues have discovered that the fog, originating offshore from some of the richest ocean waters on the planet, arrives bearing essential nitrogen and other fertilizing nutrients such as phosphorus, calcium, and sulfur. Ajit Subramaniam, an oceanographer at the Lamont-Doherty Earth Observatory at Columbia University, says the droplets in the fog contain a high concentration of these nutrients and transport that life-supporting material high up into the mountains. “Most nutrients flow from land to ocean, not ocean to land, especially in these amounts. It’s almost counterintuitive,” Subramaniam says.
Without the fog from the ocean, Weathers and her colleagues suggest, the rain forest of Fray Jorge might starve to death.
Despite the often lush appearance of the terrain, the soil in a rain forest is typically nutrient-poor compared with, say, the soil of the American Midwest, which is rich enough to support most of our farming. The enormous number of plants crammed together in a rain forest compete aggressively for soil nutrients, and the abundant moisture washes out the rest. This is one reason why the fogborne nutrients, particularly nitrogen, are so important to Chile’s pocket rain forests.
Weathers first came to Chile in the late 1980s and worked for more than 10 years in the southern extreme of the temperate rain forest belt, in Punta Arenas, Torres del Paine National Park, and Chiloé Island. More recently she joined a group of Chilean collaborators at northerly Fray Jorge because she wanted to work in a forest where the climate is much drier, and hence the influence of the fog is more clearly separated from that of the rain. “The place to understand how fog affects the maintenance of forest is not where there is six meters [20 feet] of rain a year in addition to fog,” she says.
These fogs are a local result of enormous global processes, not all of which are completely understood. Weathers has brought together scientists from different disciplines to decipher this natural system. Low-lying coastal regions like Chile’s are subject to advection fog, where warm ocean air crosses a band of cold water before reaching land. The band of cold water off Chile’s coast is produced by the Humboldt Current, a slow northerly ocean flow that runs more than 3,000 miles along the Pacific coast of South America, from southern Chile all the way to the equator. The warm air pulls moisture off the cool ocean, and onshore winds at night help drive the resulting fog inland.
