The Humboldt Current runs north with a bend to the west. This moves water away from the coast, causing upwellings that bring cold, nutrient-rich water from the ocean floor to the surface, where it feeds innumerable microorganisms and algae. These waters are home to one of the most productive marine ecosystems on earth. But the recent discovery that they share their nutrients with the land was unexpected. Weathers believes that “winds and waves kick surface scum high into the air, where it can be incorporated into the fog that moves inland.” Fog water can hold concentrations of nutrients or pollution 5 to 300 times greater than what rain can carry, she says.
Human pollutants—not natural nutrients—are what first set scientists looking at the chemistry of fog, following fatal smog clouds that settled over Donora, Pennsylvania, in 1948 and over London in 1952. In the 1980s fog grabbed attention again in the United States when researchers found it was contributing to the damage caused by acid rain. Weathers and other scientists determined that clouds and fog were major carriers of acid and other pollutants, transporting them even to remote places such as the White Mountains of New Hampshire and Great Smoky Mountains National Park. Acidity in all forms of moisture was causing stunted growth and injury to forests, researchers realized. “Although the clouds did not always deliver a huge amount of water relative to rain, they had a huge amount of pollution,” Weathers says. Fog is essentially a ground-level cloud, so it can transfer pollutants to vegetation without the need for rain.
Scientists and policymakers then needed to know how the acidity of the polluted clouds and rain compared with that found in a pristine environment. Lacking detailed historical records of what substances were typically found in American rainwater prior to industrialization, researchers decided to measure the next-best thing: unpolluted rain from the most remote regions of the world. This is what prompted Weathers to assemble a full set of fog-sampling equipment and head for southern Chile, a location that had the cleanest rain measured anywhere. She and her colleagues learned that even there the fog was acidic, although not nearly as acidic as it then was in the eastern United States. The fog also contained much more nitrogen than expected. Weathers wondered where it came from, sparking a search that eventually uncovered the critical moisture and nutrient roles of the fog originating over the Humboldt Current.
Forest ecologist Juan Armesto of the Universidad Católica de Chile, who collaborates with Weathers, says that the country’s modern coastal rain forest represents small fragments of what must have once been a contiguous forest, connected to the Amazon Basin, that changed gradually over the past 5 million to 25 million years due to the colossal upheaval that created the Andes Mountains. When the Andes were not yet fully uplifted, this forest extended unbroken from east to west, as documented by many plant and animal species that have close relatives on both sides of the mountain range. Over time, trees in Chile evolved with special branching systems to capture fog because of the need to grab sustenance out of the air. “If you are there to capture fog, height is not as important as branching,” Armesto says.
An analogue to the Chilean rain forests exists in the United States. The coast near Fray Jorge basks in a mild, Mediterranean-type climate similar to that of the famous coastal redwood forests of California, an area with long summer droughts. Despite being in different hemispheres and featuring very different species, these two forest systems have an important commonality: They both exist along coastal mountains that front highly productive marine systems—the Humboldt and California currents.
When major banks of fog invade these forests, tree canopies intercept the wind-driven water droplets via branches and leaves or clusters of needles that extend into the air. In most trees, sap flows from the roots, up through the trunk to the branches and leaves. But studies in California’s coastal redwood forests show that sap flow sometimes runs in reverse during fog events, with captured water moving from the atmosphere into the leaves and then down through the branches—something that may be happening in Chile as well. Fog may also help sustain trees simply by wetting the leaves, which prevents the release of interior moisture into the air.
Tracking the movement of nitrogen is much harder, but Armesto and Weathers believe that the nitrogen transported by fog is also critical to the survival of Chile’s coastal rain forests. “These forests recycle a lot of their nutrients from the leaf litter, and they also keep their leaves for several years rather than lose them each fall,” Armesto says. “Such processes help retain a large amount of the nutrients the forest takes in, but the main source of fresh nutrients is the fog.”
Researchers are still trying to quantify the percentages of nitrogen obtained from fog versus other sources, such as rain. But Weathers believes fog delivers significant quantities of nitrogen to Chile’s coastal forests, where growth is limited by a lack of this critical nutrient.
The fog forests are sensitive measures of every aspect of the environment, including atmospheric movements, ocean currents, pollutants, and nutrients. Climate change therefore poses special dangers to Fray Jorge and other fog forests around the world. Alterations in air and sea temperatures could lower fog frequency, for instance. It could also elevate the fog base, moving the life-giving fog higher than the mountains the thirsty forests cling to.
In California, “Records are limited, but from what we have for the last 50 years, rainfall has become more variable,” says Todd Dawson, a professor of integrative biology at the University of California at Berkeley. “The length of the ‘fog day’ has decreased from greater than 14 hours to about 11 hours.” According to Dawson, “Changes in the frequency and amount of fog could have important impacts, not so much to the mature trees but to young trees and seedlings. And that could have profound consequences for new generations of forest.”
In Chile’s temperate rain forest, Armesto sees similar vulnerabilities. Rising temperatures could influence Chile’s inversion layer, a warm air mass that rides over the fog and contains it. It could also modify coastal upwellings and the nutrients they deliver. As a result, climate change could affect the frequency of foggy days or alter the elevation of the fog zone. “Warming should mean more fog, but that doesn’t mean more fog will be delivered to the forest,” Armesto says.
For all these reasons, fog forests are good places to watch for warning signs. “The fog forests are living on the edge and are thus harbingers of major environmental changes,” Weathers says. But they are also uniquely adaptive environments. Going back 250 years, studies of the tree rings in Chilean fog forests reveal that despite some extremely dry periods produced by El Niño cycles, the rain forests continued to produce new plants. Redwood forests have weathered these same cycles as well. Could the robustness in the face of drought displayed at Fray Jorge and elsewhere help these forests survive the next set of climatic shifts?
Just as fog forests are places to understand the sensitivity of natural systems, they are also places to look in wonder at how such systems interact and adapt. “There is a connection here between the atmosphere, the moisture it holds, and the organisms that depend upon these things that you can see, feel, and smell, which is rarely presented so graphically in nature,” Weathers says.
That is perhaps the final twist at Fray Jorge: It takes a journey into this foggy forest to perceive nature’s intricacies with true clarity.