Cloud forests are tropical or subtropical mountain forests that exist inside clouds. Found at elevations where persistent fog and low-hanging clouds wrap around the mountainside, these forests pull moisture directly from the air through their canopy, creating an ecosystem unlike any other on Earth. They cover less than half of one percent of all land on the planet, yet they play an outsized role in water supply, carbon storage, and biodiversity.
How Cloud Forests Capture Water From Air
The defining feature of a cloud forest is not rain. It’s fog. These forests sit at the altitude where warm, moist air rising from lower elevations cools and condenses into clouds, bathing the trees in a near-constant mist. The canopy then acts as a giant filter: tiny fog droplets, too light to fall on their own, collide with leaves, branches, and the thick mats of moss covering every surface. Those droplets merge into larger drops that eventually drip to the forest floor. This process goes by many names, including fog drip, cloud drip, and horizontal precipitation.
Without trees to intercept them, those fog droplets would mostly stay suspended in the air. On bare soil, direct fog deposition amounts to almost nothing, roughly 0.2 millimeters per day. But with a forest canopy doing the work, the numbers change dramatically. In one study in eastern Mexico’s mountain region, fog interception contributed a volume of water 22 times greater than rainfall alone, accounting for 91% of total water input to the system during the monitoring period. A single pine tree in the same region captured enough water during a four-hour fog event to supply a family of four for over a month.
Where Cloud Forests Grow
Tropical cloud forests exist in about 60 countries, concentrated in a band within 23 degrees north and south of the equator. They typically form between 1,000 and 3,500 meters in elevation, with the upper treeline reaching 3,500 to 4,000 meters on the tallest peaks. The exact altitude depends on local conditions: on small oceanic islands, persistent clouds can form much lower, while on large continental mountain ranges, the cloud belt sits higher.
Major cloud forest regions include the Andes of South America, the highlands of Central America and southern Mexico, the mountains of East Africa, Southeast Asia (particularly Borneo and New Guinea), and parts of the Caribbean. Smaller remnants exist on volcanic islands like Madeira, the Canary Islands, and Hawaii. Despite spanning dozens of countries, the total area is tiny. These forests cling to narrow elevation bands on mountainsides, making them naturally fragmented and small.
What Makes the Ecosystem Unique
Step into a cloud forest and the first thing you notice is that everything is covered in something else. Mosses, ferns, lichens, and flowering plants blanket every trunk, branch, and rock. These are epiphytes, plants that grow on other plants without parasitizing them, drawing moisture and nutrients from the air and rain instead of soil. About 10% of all vascular plant species on Earth are epiphytes, spread across roughly 900 genera and 80 families. But their abundance and diversity peak in humid montane forests at middle elevations, precisely where cloud forests sit.
Five groups dominate: orchids, bromeliads, aroids (the family that includes philodendrons), peperomias, and ferns. Together these account for 85% of the more than 27,600 epiphyte species recorded worldwide. In a single cloud forest tree, you might find dozens of orchid species, bromeliads holding miniature ponds in their leaf rosettes (which become habitat for frogs and insects), and ferns that start as small trunk epiphytes before growing into climbing plants with roots that eventually reach the soil below.
The trees themselves tend to be shorter and more gnarled than those in lowland tropical rainforests. Trunks are often twisted, branches crooked, and the canopy lower and denser. This stunted growth is partly a result of the soil conditions. Cloud forest soils are typically waterlogged and acidic, which slows decomposition. Nutrients like nitrogen, phosphorus, and calcium cycle slowly because microbial activity is suppressed by the cool, wet conditions. Leaf litter accumulates into thick organic layers rather than breaking down quickly as it does in warmer lowland forests.
Water Supply for Millions
Cloud forests function as natural water towers. The moisture they strip from passing clouds feeds streams and rivers that flow downhill to agricultural valleys and cities. In eastern Mexico, researchers found that fog represented a 33% savings in groundwater consumption for surrounding communities. Nearly half the fog volume absorbed by the soil went beyond replacing what plants used, generating surplus water that recharged aquifers and fed springs.
This matters most during dry seasons, when rain stops but fog persists. Many tropical mountain communities depend on cloud forest watersheds for drinking water year-round, and the fog-capture function keeps streams flowing even when it hasn’t rained in weeks. Deforestation in these zones doesn’t just remove trees. It removes the mechanism that turns clouds into usable water, directly reducing supply to downstream populations.
Carbon Storage Capacity
Cloud forests punch above their weight as carbon sinks. On average, mountain cloud forests store around 384 metric tons of carbon per hectare, more than double the upper range of temperate coniferous forests (67 to 177 metric tons per hectare). The majority of that carbon sits in the soil rather than in the trees. In studied sites in Mexico, soil held over 50% of total carbon stocks, with values ranging from 68 to 198 metric tons per hectare. Above-ground biomass contributed another 43 to 117 metric tons per hectare.
That heavy soil carbon load is a direct consequence of the slow decomposition rates. Cool temperatures, constant moisture, and acidic conditions mean organic matter accumulates over centuries. The thick, spongy soil layers in cloud forests are essentially long-term carbon warehouses. Disturbing them through logging or conversion to agriculture releases stored carbon rapidly, turning a sink into a source.
Threats From a Warming Climate
Cloud forests face a threat that other ecosystems don’t: the clouds themselves can move out of reach. As global temperatures rise, the altitude at which air cools enough to form clouds shifts upward. This is known as the lifting cloud base hypothesis. For every degree of warming, the cloud base rises roughly 100 meters. That may not sound like much, but for a forest that depends on being immersed in fog, even a modest shift can be devastating.
On tall mountains, the forest could theoretically migrate upward to follow the clouds. But many cloud forests sit on mountains of moderate height, where there’s simply no room to move. The forest is already near the summit. When the clouds lift above the peak, the trees lose their primary water source, and the species adapted to those conditions face what researchers call “mountaintop extinctions.” Modeling suggests that a 1°C warming with a corresponding 100-meter cloud base lift would reduce cloud forest extent across the Americas and Africa, though some areas in Asia might see expansion as broadleaf forests shift upward.
Deforestation compounds the problem. In many regions, the treeline has already been pushed downward by farming, grazing, and burning. This shrinks the elevation band available for cloud forest from both ends: human activity pressing from below, rising cloud bases pressing from above. The result is a narrowing strip of habitat with nowhere to go, in an ecosystem that already occupies less than half a percent of Earth’s land surface.