Monteverde's cloud forest is an otherworldly haven, but the fog that should shroud it in water are rising, drying out its spectacular hanging gardens. Jocelyn Timperley reports.
On the misty Tilarán Mountain Range above Monteverde in Costa Rica, a rare combination of circumstances has led to something special.
A pocket of forest constantly shrouded in thick cloud supports an enormous variety of specialist plants and animals. For many of them, this is the only place on Earth they are found.
The ecological diversity of this cloud forest beggars belief. Some 400 bird species live here, from the spectacularly loud three-wattled bellbird to the long-tailed manakin, famed for its males' courtship dance . Sloths, black-handed spider monkeys, jaguars, pumas and Baird's tapirs roam below the thousands of tree species which droop with dense carpets of plants. Dozens of unique amphibians thrive in the moist climate, and so many insect species they have never even been counted.
But all is not well in this cloud forest, or many of the other patches of tropical cloud forest scattered across the world. Because it's becoming increasingly clear that the clouds that bring these forests to life are beginning to drift away.
As the clouds lift, the forest world below is being transformed.
"When I first came to Costa Rica and had my first look at the cloud forest, I was like 'Oh my God', look at all these plants, look at all these epiphytes.'"
Ecologist Nalini Nadkarni and I are walking through the Bosque Eterno de los Niños (Children's Eternal Rainforest), a swath of cloud forest in northwestern Costa Rica around the size of Baltimore made up of a mix of pristine forest and reforested areas.
Cloud forests are a specialised type of rainforest almost constantly enveloped in mist and fog.
Most are found in high mountains in the tropics sitting relatively near the ocean. These form due to the steady easterly winds which carry evaporated ocean water upslope, where it cools off and condenses into small droplets of fog.
Tropical cloud forests make up only 0.4% of the Earth's land surface , but support 15% of all birds, mammal, amphibians and tree fern species, half of them found only in cloud forests.
When she first visited Monteverde in 1980 Nadkarni quickly became obsessed with epiphytes – a term for the hundreds of plant species , from orchids and bromeliads to mosses, ferns and lichens. Epiphytes sprout from every visible surface in the cloud forest, never touching the ground and gaining all their water and nutrients from the fog. In the 1980s, she says, nobody really knew anything about their ecological roles.
The trees here literally creak under the weight of their epiphytes. Climb into the canopy, says Nadkarni, who is now a professor at the University of Utah, and you find horizontal branches covered with them like carpets .
Epiphytes have evolved many ways to capture the water and nutrients from cloud forests' constant mist. It's orchids, though, that are the most diverse epiphyte family in Monteverde , with some 450 species. "Sometimes we're sitting on branches that have literally $10,000-worth [£7,500] of orchids," says Nadkarni. "It's so amazing."
The vast majority of the non-woody biomass of Monteverde's cloud forest is made up of epiphytes, while their ability to absorb nutrient-dense mist means they have a disproportionately high importance for other species too. "They're actually augmenting the amount of nutrients and providing these inside the forest to circulate internally," says Nadkarni.
It's still not known exactly how many epiphytes species exist in these forests, nor what proportion of them are found nowhere else – one of the many areas of research now trying to catch up even as the warming planet begins to change this ecosystem.
So what happens if the clouds lift, and these plants stop having year-round mist to drink? Their world gets torn apart. "These forests here will go, 'Yikes, we're caught with our pants down. We don't have any mist and fog'," says Nadkarni.
Scientists call it the " lifting cloud base hypothesis ": warming temperatures due to climate change mean the mist keeps rising upward until it misses the mountains altogether, changing how frequently the plants and animals are immersed in cloud.
"And it's already happening?" I ask Nadkarni.
"It's already happening. We're already seeing effects."
Researcher Alan Pounds, a scientist at the Monteverde Cloud Forest Preserve, first proposed this lifting cloud base hypothesis in the 1990s. "It's been shown in lots of different areas that it is happening," he tells me, from the Andes to East Africa.
Scientists including Pounds have been collecting data on the moisture in Monteverde's cloud forest since the early 1970s. In 1999, he and two colleagues published a paper warning the number of dry days – measured as days when a standard rain gauge fills less than a 10th of a millimetre, used as an indicator of mist and cloud water – had drastically increased, and was increasingly coalescing into runs several days long.
"If you look back at the '70s, it was rare to have more than 25 days of the entire year where we weren't recording precipitation," he says. Through the 1990s, it was 59. Between 2015 and 2023, his preliminary, unpublished analysis indicates an average of 119 rain-free days each year, he says. Since 2002, he has additionally been collecting long-term data on mist and cloud-water to help make sense of it all, he says. Final results are imminent.
"[A cloud forest] is a mountain immersed in clouds," he says. "Or it's supposed to be, that's part of the problem – a lot of that is changing."
There are several other concerns about climatic changes to this cloud forest. In the dry season, wet days appear to be getting wetter, and dry days drier. "So far we're not seeing a decline in total precipitation," says Pounds. "[But] we're seeing more and more contrast." The size of the cloud bank may also be shrinking , says Pounds, though notes this is unconfirmed.
Because they appear near mountain tops, typically above 1,500m (4,900ft), cloud forests tend to be far smaller than lowland forests like the seasonal rainforest that makes up most of the Amazon and lacks these year-round, low-lying clouds. In Monteverde, you can drive for five minutes and find yourself in a completely different microclimate.
The mountaintop location also means species are often isolated, and thus endemic – native only to one (in this case, often very small) area. It makes them particularly susceptible to extinction .
Monteverde has already been the site of the most famous impact of the changing climate on cloud forests: the disappearance of the famous golden toad in the late 1980s. Living in only a tiny area of the cloud forest, the golden toad stayed buried underground for most of the year, emerging every spring to mate.
"You'd see these bright orange male frogs jumping around looking for females," says Nadkarni.
In 1987, over 1,000 golden toad adults were seen mating . By 1989, only a single male was spotted . The next year none. The golden toad is now presumed extinct . The likely cause: a deadly mix of climate change , an invasive fungus and a strong El Niño year – a weather phenomenon that pushes up global temperatures – which produced an exceptionally dry season . Pounds' and others research has since documented huge losses of frogs and toads linked to climate change and the Batrachochytrium dendrobatidis fungus .
The loss of species like the golden toad is a sign the habitat is in flux. One way to view the impact of the changing climate on the cloud forest, says Pounds, is that "it's turning into a seasonal rainforest… more like the lowlands".
The result, he says, is that lowland species are moving in.
Not all species are happy to live in cloud forests, says Pounds, but "there are advantages… if you can deal with the conditions", such as escaping competition and predation from the many different species in lowland tropical forests.
Now, though, as Monteverde's clouds lift, temperatures rise and the forest dries out, these lowland species are being seen more and more. Keel-billed toucans – opportunistic predators of other birds' eggs and chicks – are increasingly nesting alongside resplendent quetzals , the emblematic species of Central American cloud forests, which is already threatened due to deforestation . Poisonous snakes like the terciopelo are arriving in Monteverde. Lowland bats, appear to be moving up , including the enormous spectral bat, which preys on quetzals.
As the climate changes and these species arrive, they may be displacing and disrupting current residents, causing chaos in the complex, finely tuned microecosystems of the cloud forest.
Each species here has "its space, its schedules and its friends", says Daniela Quesada Cruz, community programme coordinator at the non-profit Monteverde Institute. The 75 species of wild avocado tree in Monteverde, for example, all produce fruit at different times of the year – any change and their fruit could rot with no birds visiting to disperse it.
Climate impacts mean that "you basically lose" the more specialised flora and faunas of the higher elevations, says Pounds. "It's all happening very quickly and we didn't really have the resources to do the kinds of systematic sampling of everything that we should have. It's overwhelming."
Monteverde's cloud forest is not the only one at risk. Across Mesoamerica, climate change and deforestation are driving cloud forest plant species uphill by an average 1.8-2.7m (5.9-8.9ft) per year. Worldwide, 2.4% of cloud forest cover was lost between 2001 and 2018 alone.
After the disappearance of the golden toad and decline of other frog species in Monteverde , researchers began seeing other clues of climate impacts in the cloud forest, says Nadkarni – including on trees and plants .
Cloud-loving epiphytes in particular are the "canary in the coalmine" for climate impacts, says Sybil Gotsch, a forest ecologist at the University of Kentucky. "It's the first plant community that's going to be affected… because they don't have roots that go to the ground. As the atmosphere dries out, we're going to lose those epiphytes."
In the immensely complex cloud forests, measuring the extent to which losses are already happening is hard. But studies transplanting epiphytes to trees at lower elevations and in greenhouses have shown they are very vulnerable to lower amounts of mist, and projected large future extinctions if climate change continues unchecked.
Climate change has come along fast and with so many species living here, most lack long-term studies which can give baselines for tracking changes. In 2016, Gotsch began a 10-year study to track epiphytes, only for it to be cut off by Covid-19 (she will publish a paper covering the first four years in 2027).
On a windy January day, I accompany Gotsch and Nadkarni on a visit to a farm in the cloud forest ecosystem where they are trying to understand what might happen to other species in a cloud forest with fewer epiphytes, by experimentally stripping trees of them now. "We don't want to wait 50 years [to find this out]," says Nadkarni.
Without epiphytes holding them back, for example, trees might grow more, says Gotsch – not as positive as it sounds, since they could use up yet more water.
They show me two pairs of strangler fig trees; in each case, one has been stripped of its dense mat of epiphytes, the other left as a control. They have eight other similar tree pairs dotted around Monteverde.
Now they are measuring everything they can think of which might change in an epiphyte-less tree: from the surrounding temperature, humidity and wind speed to sap flow, leaf appearance and use by wildlife.
Countless other changes could be occurring here out of sight.
Pounds tells me of "painfully obvious" declines in insect numbers, judging simply by how many appear around lights at night. (Ecologists in the nearby region of Guanacaste have similarly noted a huge drop in insects, including in its cloud forest, which they attribute to climate change .)
Debra Hamilton, co-director of the Costa Rican Conservation Foundation (CRCF) and a restoration researcher at the University of Vermont, is similarly concerned by her observations of the decline in insectivorous birds. "That, I believe, is the canary in the coal mine," she says.
Hamilton, Pounds and other researchers are now conducting insect sampling and bird surveys in Monteverde to compare numbers with past data . A current worry is the ongoing super El Niño . "This upcoming year is projected to be very dry," says Nadkarni. "The canopy is likely to be hit hard." Hamilton notes that this year October, usually the wettest month, has been astoundingly dry. "It is the first time that I know of a weather alert for drought conditions during a month when we get an enormous amount of rains," she says.
What is the ultimate fate of the cloud forest's ecology under continuing climate change? One result could be a novel ecosystem : the new self-organising mixes of native and non-native species created by human influence that are increasingly common around the world .
Still, it's not at all clear which, if any, of the cloud forest specialists might survive, says Pounds. It's impossible to predict, he says, what this ecosystem will become.
Monteverde is something of a green trailblazer . The area is protected by a patchwork of national parks and private reserves set up in the 1970s and '80s conservation boom and Monteverdeños are largely well informed about sustainability and their environment.
Decades of ecological tourism in Monteverde has supported conservation, says Quesada Cruz, encouraging locals to move from farming cattle to providing night walks, zip lines and canopy tours – keeping trees on their land in the process. But she believes tourism may be reaching a limit of sustainability. In some places that had been reforested, she says, developers have now cleared the forest and built new hotels.
Long term efforts are creating corridors to connect the cloud forest with areas outside reserves , much of it private land, helping to create space for species to move and migrate. The Monteverde Institute hands out some 10,000 native trees per year to locals – creating both animal corridors and windbreakers for farmers in the area's windy terrain. There's a push to plant native species in gardens.
Ensuring connected habitats, along with wider restoration and protecting forest from development, fire and cattle, are still essential to protecting the cloud forest, says Katy VanDusen, coordinator of local climate non-profit organisation CorClima.
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What gives hope in Monteverde, she adds, is the community here. "What is really unique about here is how the community has worked together in creative ways for decades to solve problems, and really with a big commitment to conservation."
I ask Hamilton, a reforestation scientist who has been restoring habitat in Monteverde for decades now, whether conservationists might ever end up feeling forced to intervene in these native forests, moving trees species around to help them and the wildlife they support adapt?
"That's a big question," she replies. Older scientists, she says, have been trained rigorously to never introduce trees into new areas. "In my book, it's playing God. But on the other hand, we may need to do this… Because climate change really is happening."
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