In traditional Q'eqchi' Maya expression it is said "the forest catches the clouds (li kiche' naxchap li choq)." This is exactly what a cloud forest does. Cloud forests catch clouds. Or in the parlance of biologists, cloud forests filter clouds in a process called lateral cloud filtration. Clouds blow in among the trees as moisture from the ocean moves inland, encountering mountains. Water droplets (like the one pictured below) collect on the leaves of the trees of these forests through the process of lateral cloud filtering. In many cases, cloud filtration accounts for more than half of the annual precipitation in cloud forests.
Cloud forests are like rain forests in that they generally receive high levels of precipitation. The difference is that with cloud forests, much of that precipitation comes directly from the clouds that filer through the trees.
There are cloud forests all over the world. People usually think of cloud forests as uniquely tropical. However, lateral cloud filtering happens in temperate regions as well.
Take a walk along Cape Lookout Point on the Oregon coast. The hemlocks and Sitka spruces stand like towers along the rugged coast. Ocean breezes pushing moisture in from the Pacific is almost a constant here. Moisture from the clouds condenses as it touches the tree tops. The condensed water forms tiny droplets. Epiphytes growing on the massive trunks of the spruce trees are the first to catch the water.
Walk under these trees on a cloudy, breezy day and you would think you were in a rain storm. Walk out into the parking lot of the trail head and you will notice that it is not rain at all. Annual precipitation in the nearby village of Cape Meares is 65 to 90 inches. Under the towering cover of the mature hemlock and spruce forest, the annual precipitation is 150 inches to 200 inches.
Similar dynamics of lateral cloud filtration occur all along the pacific coast. From the forests of the Kenai peninsula near Seward, Alaska, to Cape Scott on Vancouver Island, to Quinault, Washington on the Olympic peninsula, to Khwunrghunme, California among the towering Coastal Redwoods. In these forests a large percentage of precipitation comes from directly from cloud filtration. Thus these forests can be, and perhaps should be, considered cloud forests although they are often referred to as temporate rain forests.
Cloud forests are more common in the tropics. They are green, growing, glowing gardens of bromeliads, ferns, orchids, and mosses. They are steep slopes of laurel trees and ridges of magestic oaks. They are acidic bog like soils drenched with moisture. Whether in Borneo or Hawaii, the Canary Islands or Costa Rica, tropical cloud forests filter clouds and this filtration accounts for much of their annual precipitation. In the tropics these forests are sometimes called fog forests. Generally cloud forests are higher than rain forests but not always. The atmospheric conditions that create a cloudy or foggy environment can happen at any altitude. But it is generally true that cloud forest are high (1,000 to 3,000 meters above sea level). In Guatemala, cloud forests can be as low as 900 meters above sea level. All these forests have in common the fact that while the fog or clouds diminish the amount of direct sunlight, they greatly increase the amount of precipitation.
Total precipitation means both rainfall and the water collected through cloud filtration. Total annual precipitation in tropical cloud forests can be as high as 275 inches to 385 inches. "The extra water-trapping capacity [of trees through cloud filtering] can be as much as 60 percent" (John Roach, National Geographic News, Aug. 2001). Using Roach's numbers, this means that the 385 inches of precipitation would be reduced to 155 inches if the trees were removed.
The cloud filtration that happens in these forests increase ground and surface water making these forests virtual water factories. To give one concrete example: the cloud forest of La Tigra National Park in the mountains above Tegucigalpa, Honduras, has a mere 18km x 16 km area of cloud forest. Yet this single forest provides 40% of the water used in Tegucigalpa, the capital city of Honduras with its 1.25 million inhabitants.
Although some 30% of Guatemala is still primary forest, less than 2% of Guatemala is cloud forest. Remote, rural communities and urban areas alike get their water from the springs and streams replenished from these cloud forests. Although they account for a small percentage of the landscape, they account for a large percentage of Guatemala's water. Cloud forests are the living aquifers of Guatemala. Turn on your shower in any hotel in Antigua and you have a direct connection to the cloud forest el Pilar on the Volcano Agua. If your bathroom window faces south you can see the cloud forest from which your water is coming.
Visit Zacapa and the villages of the Motagua valley, one of the driest regions of Guatemala. The water systems of these villages and irrigation systems of these farms are all connected to the cloud forests of the Sierra de las Minas. The town of San Rafael de la Cuesta in western Guatemala bought a small section of cloud forest from a neighboring village specifically to insure their municipal supply of water.
The approximate 800,000 inhabitants of the Cahabon watershed derive their water from the cloud forests of the Sierra Chama, Sierra Yalijux, and the Sierra Sacranix. More on water as a resource.
In Guatemala, cloud forests are found:
- along the volcanic corridor of the western highlands,
- in the central highlands,
- along the Sierra de las Minas,
- on the north slope of the Cuchumatanes,
- and the el Triunfo forest on the Guatemala, Honduras, El Salvador border.
Of these areas, the largest contiguous cloud forest is that of the Sierra de las Minas. The cloud forests of the central highlands, e.g. Sierra Yalijux and the Sierra Sacranix, are more fragmented due to human impact but of equal importance ecologically.
Guatemalan Cloud Forest Ecology,
October 15, 2001, we hike from Montane pine-oak of Rio Matanza, Baja Verapaz, up into the cloud forests above La Union. The walk is only 5 kilometers but we can see big changes as we move from one kind of forest to another. It's a sunny day. In the pine-oak forest, the sun feels warm on our backs, especially in the clearnings. Is it just a coincidence that a cloud rolls in just as we being to notice fewer pines? The amount of direct sunlight is diminished. The sky is no longer deep blue but a grey-white. Now the brightness is not coming from the sky but from the objects around us. The sun is not shinning but the leaves are. With less sunlight the rate of evapotranspiration diminishes as well. You can almost feel as if the pulse-rate of the earth has dropped; perhaps in the cloud forest the earth is at rest.
Laurels replace pines. We notice more epiphytes and mosses on the trees. In fact, some trees are so completely covered with other plants that it is hard to see the host tree. Enormous fern trees now tower over our heads. Through the fog we hear Howler Monkeys (Alouatta pigra). The air is distinctly cooler but we have not gained much elevation. The ground below our tread has changed as well. We have left the noisy, dry pine needle and oak leaf carpets of the pine-oak forest. Now we are walking on sponge-like ground, reminiscent of bog land in the boreal (taiga). Above us the trail continues to climb. Far off, we hear the two note call of the Resplendent Quetzal. It almost feels like we are on another planet.
We will save the last part of the hike for another day, but if we were to continue to climb to the ridge and follow it along, the character of the cloud forest would change yet again. Massive oaks dominate the ridges, mixed with an occasional pine, and towering tree ferns. Here we might be lucky enough to see the Pink-headed Warblers. These massive oaks tower over the other trees along the ridge.
A mature oak cloud forest produces 28,373 pounds of leaflitter per hectare per year (Kohler et al. 2006). This annual deposit across the thousands of hectares of cloudforests adds up to a sizable carbon lockbox, helping to counter atmospheric carbon pollution.
We step out onto a limestone outcropping. Long ago, this rock was the ocean floor. Geologically speaking, the mountains of the central highlands are young. Taking that geological long view of things, these oak and laurel cloud forests have only recently arrived from the north.
The biodiversity and endemism are especially high in tropical cloud forests (an endemic is a species found only in one area). To further understand this phenomenon in Guatemala's cloud forests, let's reach for what may seem an esoteric corner of research: Dr. Jack Schuster, Entomologist at the University del Valle of Guatemala, studied endemism among Coleoptera: passalid beettles in the cloud forests of Guatemala. He found extraordinarily high levels of endemism in the cloud forests. His findings illustrate the ecological character of Guatemala's cloud forests. Endemism is so high, not only among among beetles but among orchids and other vascular plants, insects, amphibians, reptiles and even a few species of birds that it would be possible to say that each cloud forest is unique.
The beettle in the photo (left) is endemic to the cloud forests of just a few volcanos along Guatemala's volcanic corridor. Each volcano's cloud forest is altitudinally isolated from other forests by the broken topography of peaks and valleys. These isolated forests are the ideal venue for the species and subspecies that are branching out from evolution's family tree.
Cloud forests are a treasure trove of biological diversity. Here are a few more examples.
Köhler, L. et al. 2006. Above-Ground Water and Nutrient Fluxes in Three Successional Stages of Costa Rican Montane Oak Forest with Contrasting Epiphyte Abundance. In Ecology and Conservation of Neotropical Montane Oak Forests, ed. Maarten Kappelle. Berlin: Springer.