The uppermost layer of a forest plays many critical roles, including guarding against climate change. Saving them is imperative, says a biologist on an ambitious quest to reveal and protect canopies.
Meg Lowman was a fresh-faced 22-year-old when she arrived in Sydney, Australia from her native New York in 1975 to do a PhD in botany. It was the first time she had ever set foot in a rainforest, and the learning curve was steep. But one lesson in particular stood out.
“I realised that most people were only studying the forest floor and tree trunks, missing 95% of the forest,” says Lowman. It was an approach that seemed alarmingly narrow to her. “It’s like a doctor staring at your big toe and forgetting that there are a lot of important body parts in your upper half too.”
The realisation was a watershed moment for Lowman, who decided to dedicate her career to illuminating the mysteries of life in the treetops. More than four decades on, the monikers she has gathered say it all: mother of canopy research, Einstein of the rooftops, real-life Lorax, to name a few.
Only a handful of people have ventured where she has and witnessed the beauty of a realm she calls “the eighth continent.” Lowman is now striving to change that. She’s on a quest – named Mission Green – to build a network of treetop walkways around the world. The aim? To make forest canopies more accessible and less obscure to the everyday person.
People are more likely to protect and conserve what they can see, she explains. “The whole underlying purpose here is that we want to save forests.”
Home to many
The canopy refers to the uppermost layer of a forest. In temperate regions, treetops average between 30 to 60 metres; while those in the tropics are roughly double that. America’s Pacific Coast and Australia’s southern region boast the world’s tallest trees – redwoods and mountain ash, respectively – growing upwards of 100 metres.
Regardless of the location, canopies play many critical roles. And with climate change intensifying, the spotlight on rainforests, which are frequently called the Earth’s lungs, has only grown more intense.
Looking at a canopy’s structure can give you a good idea of how healthy a forest is, says Geoffrey Parker, a forest ecologist at the Smithsonian Environmental Research Center in Washington, DC. “It is a very good predictor of how much biomass there is in a forest.”
Parker uses lidar, a laser sensor technology, to map the structure of canopies from a bird’s eye view. “Forests tend to get ‘bumpier’ as they get older – more full of holes and more detailed in how they’re organised vertically inside,” he says. “Those things tend to accommodate higher diversity of species, not just of trees but all the other organisms that rely on the trees.”
A staggering number of species live in the upper layers of forests. “We now believe that 50% of land-based plants, insects, and animals live in our treetops,” says Lowman.
“I have seen iguanas and various kinds of monkeys and interesting things like macaws that you just can’t see from the ground,” says Parker, who has worked in rainforests throughout the world.
Biologist Andrew Whitworth readily reels off the wildlife he’s spotted in the treetops of Costa Rica, where he heads a nonprofit called Osa Conservation: spider monkeys, silky anteaters, olingo racoons, and even small cats called margays. “Canopies have an umbrella effect – they provide habitats and food resources to so many other species,” he says.
That includes plants too. “There’s orchids and bromeliads, and also blueberry bushes,” says Sybil Gotsch, an associate professor of biology at Pennsylvania’s Franklin and Marshall College, of the canopies she’s studied. “There’s also trees within trees – I once found a 10-metre-tall hemlock tree on a branch in a pocket of soil on top of a redwood.”
“The canopy supports a very important component of overall diversity in the forest,” says Glen Reynolds, director of the South East Asia Rainforest Research Partnership (SEARRP) in Borneo, Malaysia.
That’s because it’s “the interface between the atmosphere and biosphere,” he says, where photosynthesis, gas exchange, and other important chemical processes take place. It’s also where most fruits and flowers are found, and thus where pollination occurs. “Almost all the important stuff goes on there.”
A big unknown
Yet, only an estimated one-tenth of canopy species has been studied. Access is the main limiting factor. For years, researchers had to rely on catapults and slingshots to shoot ropes over a target branch high up in the canopy and haul themselves up in harnesses. Lowman herself pioneered a number of climbing methods, many of which were inspired by spelunking and rescue techniques.
But climbing “takes time, and is exhausting and dangerous”, says Bartosz Majcher, a researcher at the University of Hong Kong who is doing a PhD on canopy ecology.
Thankfully, the past two decades have witnessed the introduction of cranes and canopy towers, and the adoption of modern technologies such as drones, lidar and remote sensors – all of which have made it easier to access canopies. But there are drawbacks too, cost being a major one. Additionally, cranes cover only a small area, while surveillance technology doesn’t always provide sufficiently granular data. And so ropes remain the go-to method at many sites.
Still, progress in treetop science can be frustratingly slow. “Canopies have been described as the last biotic frontier,” says Majcher. “Millions of species live there, and we’ve accessed only a minute proportion of them.”
“We can be sure we’re losing things before we’re finding them,” adds Lowman.
Which is where her latest conservation project comes into play. Launched in November 2020, Mission Green aims to construct 10 canopy walkways in forests that are considered biodiversity hotspots. These include sites in Mozambique, Madagascar, India, Bhutan, Peru and North America. Two – in California and Penang, Malaysia – are already up and running.
“Many, many acres of forests have disappeared and continue to disappear,” explains Lowman. “So we have to become more strategic and save those places that have future ‘genetic libraries’ for our children and grandchildren to work with.”
“It kind of shortcuts conservation if we can save a lot more species in the highest biodiversity areas first,” she says.
Vanguard against global warming
Conserving canopies isn’t just important from a biodiversity perspective, but also as a guard against climate change.
For species that dwell in the understorey, the canopy “creates a buffer to stresses in the environment” by acting as a “gatekeeper between the atmosphere and ground,” says Gotsch. The architecture and physiology of a canopy govern a forest’s microclimate, helping to keep it cooler than its surroundings by intercepting rainfall, slowing wind speed, and influencing the rate of evaporation and transpiration.
“This buffering effect is quite large,” says forest ecologist Pieter de Frenne from Belgium’s Ghent University. In a meta-analysis of more than 70 forest sites scattered across five continents, de Frenne discovered that daytime temperatures within a forest are on average 4C cooler than outside. That difference increases in hotter climes, sometimes by as much as 15C.
“That means that this thermal regulation, this protective sheltering layer of canopies becomes more important with climate change,” he says.
In addition, a forest’s upper layers help suck carbon dioxide from the air. Estimates suggest that maintaining current carbon uptake by forest canopies and avoiding emissions resulting from deforestation can deliver up to 50% of the carbon mitigation needed for us to stay within our 2C limit. That’s because protecting canopies means protecting the biggest trees, which are much larger carbon sinks compared to “lots of little spindly trees,” says Whitworth. “In terms of storage, they’re hugely important.”
A necklace of walkways
It’s for all these reasons that Lowman’s Mission Green comes at a critical juncture. The “beautiful thing” is that the walkways will help make canopies more accessible,” says Gotsch, “so that people can see, value and appreciate them, and then hopefully help to conserve and study them.”
Reynolds from SEARRP agrees, pointing to Penang’s Langur Way Canopy Walk – one of Mission Green’s two maiden walkways – as an example. “It’s really well done, I applaud them for putting in a structure that allows anybody from a five-year-old to a 90-year-old, even special needs people in wheelchairs, into a forest canopy.”
Getting to the walkway is easy. From the park entrance, it’s a five-minute stroll along a gentle shaded path. Stepping onto the 230-metre-long suspension bridge, a breathtaking vista immediately opens up: on the right, you can look to the horizon and see the glittering sea along Malaysia’s western coast, beyond the thicket of trees that is one of three virgin jungle reserves on Penang Island. To the left, the dense lushness of the tropical rainforest strikes you up close as a tangle of lianas, epiphytes and ferns amidst the crowns of dipterocarp hardwood trees. Looking down, you spot the carpeted forest floor some 40 metres away.
On a recent afternoon in late July, a half dozen dusky leaf langurs – small, friendly, seemingly bespectacled monkeys that are the walkway’s namesakes – clambered nimbly upon its railings. One dozed in the branch of a nearby tree, as Asian bluebirds and racket-tailed drongos, and even a black giant squirrel, flitted by.
“It really brings that sense of the last frontier of rainforests into people’s view,” says Reynolds, who isn’t involved in the Penang walkway but has visited numerous times.
“As an environmental education outreach facility, I think it’s amazing,” he says. Up to 300 people come to the walkway daily, and prior to the pandemic, more than 5,000 students visited every year.
Education is a key aspect of Mission Green’s game plan. In all, there are three components, says Lowman: build walkways; hire local people to operate them and educate others through a sustainable ecotourism model; and fund students to come and conduct canopy research.
For now, the Mission Green network comprises existing walkways, such as those in Penang and in Eureka, California. Two more – in Sarasota, Florida and northeastern Peru – are expected to join the “necklace of walkways around the world” in the coming months, says Lowman, and benefit from the educational activities and global marketing the project has to offer.
The remaining six Mission Green treetops walks will be built from scratch. Next up is one in Ranomafana, Madagascar, with construction slated to begin in the spring of 2023. Meanwhile, talks are underway to build another in the Great Smoky Mountains, North America’s most biodiverse national park.
When it comes to conserving forests, people talk about planting new trees, says Lowman. “Yes, that’s a fabulous thing, but a seedling can’t provide a habitat for a koala bear.”
“We need to have the big trees most of all, and it’s my job to speak for them,” she says.
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