When you walk into a tall forest it is the trunks of the trees that first meet your eye.
But look upwards and you’ll see a whole other world, and it’s one that’s taken a very special kind of scientist to discover.
Still today, after decades of research, the canopy is far less well understood than what’s down below, especially when it comes to tropical rainforests.
We do know though, that half of Earth’s biodiversity is found in tropical rainforests, and a large proportion of species are only found in the canopy.
Canopy researchers want us to understand this treetop world better — and to conserve what’s left of it.
Here’s what they say about getting high, literally, on trees.
The magical world of the canopy
Meg Lowman, aka Canopy Meg, is a pioneer of canopy research based in the United States, but her first experience of climbing into a rainforest canopy was in the Royal National Park, just south of Sydney.
Despite flailing on the climbing rope, she still managed to take in the beautifully smooth grey-white bark of the coachwood tree she was in, and its bright green, waxy, oval-shaped leaves.
As she inched her way up from the shadowy forest floor, she broke into the middle of the canopy, where she started to see flecks of sun sparkle on the leaves.
And when she finally reached the sunny and windy top of the tree, she screeched for joy.
“It was riotous, just full of life and activity and just such a magical place compared to the forest floor,” Dr Lowman recalls on ABC Conversations.
The experience changed her view forever, and now this self-described “arbornaut“ calls the forest canopy the Earth’s “eighth continent”.
Looking down on a canopy from the air, she says, is like looking at “a giant field of broccoli”.
“The canopy is not homogeneous. It’s full of … 50,000 shades of green and all sorts of bumpiness, because some trees are smaller and taller than others, and [there are] little gaps where a tree is fallen,” she says.
“And there are amazing, brilliant spots where some trees might be flowering yellow or red.
“It’s just an absolutely beautiful painting from the top.”
‘Tree climbing for grown-ups’
Biologist Nalini Nadkarni is another “elder“ in the field of canopy research.
She loved climbing trees as a kid and was overjoyed when she discovered as an adult that she could actually get paid to do it.
It’s one thing to scramble up a backyard tree, but quite another to scale the heights of a rainforest tree that might be taller than a 20-storey building.
For this, says Dr Nadkarni, a professor in biology at the University of Utah, you need “tree climbing for grown-ups”.
Dr Nadkarni has specialised in using ropes and other mountain-climbing equipment to get up close and personal with life in the canopy, something she still does today at the age of 67.
Meanwhile, Dr Lowman has pioneered the use of canopy walkways for research.
And she’s also used other contraptions like a canopy “luge“, which is dragged across the treetops by a blimp.
Then there’s the canopy raft, which allows researchers to tiptoe around on the treetops like they’re walking on the waves of the sea.
Canopy scientist Nigel Stork of Griffith University started off in the 1980s analysing insect diversity in Asian rainforests.
“We’re talking trees that were 75 metres tall in Borneo,” says Dr Stork, who specialises in entomology and ecology.
From the ground, he’d “fog” the trees with an insecticide and see what insects dropped out of them.
He’d listen as the insects fell and then scrape them into a jar of alcohol to preserve them for identification.
These days, Dr Stork prefers to hitch a ride up to the canopy in a gondola attached to a special crane — like the one he helped put in place in the Daintree forest of North Queensland 20 years ago.
“It’s a really, really great way to examine the canopy,” he says.
The crane, run by the Daintree Rainforest Observatory at James Cook University, is made of modules that were delicately put into place in the forest by a helicopter.
The crane is driven by off-site power which makes riding it an “eerily quiet experience”.
Drones and satellite imagery are also giving scientists new ways to explore canopies.
“People who have never even climbed a tree are answering questions about the forest canopy using these new remote–sensing tools,” Dr Nadkarni says.
“It allows them to look at the canopy at far larger spatial and temporal scales than what I, as a single researcher with a little backpack of gear, can do.”
Amazing discoveries in the canopy
In its short life, canopy science has revealed some weird and wonderful things about the “eighth continent”.
Dr Nadkarni’s research has focused on Costa Rica’s Monteverde cloud forest, where a “nutrient soup” of warm moist air feeds a community of epiphytes clinging to branches in the canopy.
Think orchids, bromeliads, and bird’s nests ferns, but also mosses and lichens and liverworts, perched high where they can get access to life-giving sunlight.
Dr Nadkarni’s early research found that epiphytes were so abundant in the cloud forest, they made up four times the biomass of all the tree leaves put together.
And by sitting for countless hours in the forest canopy, she discovered 56 of the 193 bird species in the world that relied on epiphytes lived up there too.
Some of these relied almost entirely on canopy plants for foraging — eating epiphyte fruit or gathering moss to adorn and camouflage their nests.
Soil in the treetops?
Dr Nadkarni was also astonished when she found tree branches in the cloud forest canopy wrapped in a living “rug” of canopy soil, sometimes 40 centimetres thick, bound together with epiphyte roots.
These soils, rich in carbon and nutrients, are formed mostly from decomposing mosses and other epiphytes, and they even contain earthworms and fungi!
Dr Nadkarni found 33 metric tonnes of canopy soil per hectare in the forest — about twice the size of a football field — and was particularly excited to discover that some host trees had special “canopy roots” to tap into these elevated soils.
Other research suggests these canopy soils could even play an important role as a carbon sink.
While the canopies of tropical cloud forests have an extreme level of biomass and diversity, Dr Nadkarni says the canopies in other forests, including in Australia, are just as important to understand.
Insect ‘salad bar’
Apart from birds, many other animals can live in a forest canopy, including frogs, snakes and mammals. But insects rule.
Dr Lowan likes to call the canopy the “salad bar for insects” — everything from parasitic wasps, ants and flies to sap-sucking bugs, beetles, and butterflies.
Dr Lowman’s research showed how plants and insects in the canopy engage in “biochemical warfare” – with plants producing toxins to discourage being eaten by insects and insects evolving to be able to digest these toxins.
The exact number of species that exist in the “eighth continent” is still uncertain, but Dr Stork’s research has contributed to the numbers here.
His early work in Borneo found a cup of tiny insects from the canopy contained about 5,000 species, and a staggering 24,000 individuals.
“Twenty-five per cent of all species that have ever been named are beetles,” he says, adding they’re are a good indicator of just how biodiverse a forest canopy is.
Dr Stork’s research found about half of the beetle species in the Daintree lived in the canopy.
But by number, ants are the king of rainforest canopies. That’s certainly the case in Australia, where Dr Stork’s early research found they were feeding off high-energy nectar secreted by trees and “honeydew” secreted by sap-sucking bugs.
Change is in the air
These days, canopy researchers are spending more time looking at threats to the canopy, including climate change, with one particular concern being the drying trend seen in many tropical rainforests.
Dr Stork says preliminary results from one experiment he’s involved in suggest drought conditions make the honeydew-eating canopy ants change their diet to eat other insects.
“They’re not getting as much food from sap-sucking bugs or from the extra floral nectaries, and so they resort to becoming more predatory,” he says, adding this could have flow-on impacts for canopy ecology.
Meanwhile, Dr Nadkarni says there is a concerning trend of less moisture in cloud forests and she is studying the impact of this on epiphytes and the birds that depend on them.
Once focused on exploring the beauty of pristine forests, Dr Nadkarni is now looking at areas affected by deforestation and fragmentation.
“My own career has shifted … to landscapes that are deeply touched by human activities and trying to understand before it’s too late what are the implications of this.”
“I feel like that’s what I kind of have to do now.”
Like Dr Nadkarni, Dr Lowman is also driven by the need to conserve the wonders of the “eighth continent”. And to counter economic pressure to log forests, she’s putting canopy walkways to another use.
As she recently told the Science Show, she wants to build walkways in endangered forests around the world to encourage tourism instead of logging.
“We really hope that by creating some ecotourism opportunities in these last high-biodiversity places, we can show local people the value of keeping the trees, but making money at the same time.”
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