A light, pre-morning
rain is falling as Vivek Ramachandran climbs on his motorcycle and careens on
to the fog-shrouded dirt track that winds through the Kalakkad-Mundanthurai
Tiger Reserve (KMTR) in Tamil Nadu. The forest seems at times to close in on
the track, the dense tangle of undergrowth cutting across it every once in a
while. Above, layer upon layer of tree canopy forms a dense patchwork that
masks the sky.
Ramachandran’s destination is a patch of dense evergreen forest called Kakachi-Kodayar, on the saddle of a hill range that forms a gentle undulating plateau. Reaching the site, he abandons his motorcycle, switches on his headlamp, and stumbles through a dense wall of liana-festooned vegetation. He stops at the base of a Cullenia exarillata (wild durian) tree, the dominant species in this forest. It barrels 35 metres up to tower above all the others.
The guide wire is still in place. Using it he raises his climbing rope, and once it’s safely anchored, wriggles into a harness. Then, with the dexterity of a rock climber tackling a vertical face, he starts his ascent. Five minutes later, he’s perched on a small wooden platform wedged 30 metres up in the canopy. The first rays of the sun are just hitting the treetops, and a new set of creatures is stirring.
It is a universe on its own—buffeted by wind, lashed by rain, and burned by sun, rich in fruit, flowers, insects and a variety of birds and mammals. It is an ecosystem that is only now beginning to be documented and understood.
From the air, the canopy looks like a vast expanse of green. As you descend, it resolves into a dense mesh of trees, hidden from the ground by intervening layers of foliage. Even its inhabitants rarely go down to the forest floor, preferring to move along the aerial pathways formed by the interlocked branches.
Some, like the ghoulish lion-tailed macaque and the similar but slightly more benign-looking Nilgiri langur are obese, says Soubadra Devy of the Ashoka Trust for Research in Ecology and the Environment (ATREE), the pioneer of canopy research in India. “Yet I don’t think they need to come down to the ground to get around.”
***
Perched on his ledge,
34-year old Ramachandran is like Alice, up in Wonderland.
Even the norms of the treetops are different. The flocks of birds here are mixed, rich in variety of species. Their descent is announced by the garrulous calling of the racket-tailed drongo, a black, rakish-looking bird with a flourish of curved feathers over its beak and two coattails that flap behind it. Then come warblers that flit from tree to tree, and small but dazzling birds like the velvet-fronted nuthatch and the grey-headed canary flycatcher that are after insects.
A great black woodpecker, a big bird with a punk-like red mane, perches a few inches from Ramachandran’s ear. Up here, creatures are inquisitive and fearless, remarkably different from their wariness on the ground. A few metres away, a male great pied hornbill feeds the self-incarcerated female through the gap in their tree-hole nest. A lion- tailed macaque sneaks up to tug at the researcher’s backpack.
As the sun climbs into the sky, a “very large” centipede makes its way along a branch; and a Calotes grandisquamis, a large iridescent green lizard found only in the Western Ghats, suns itself on a branch 30 metres up.
Most of us who venture into the forest never see this world that exists on the tops of trees. According to Soubadra Devy, this is the last biotic frontier, housing nearly 50 per cent of the biodiversity of terrestrial ecosystems.
Most of us who venture into the forest never see this world that exists on the tops of trees.
According to Soubadra Devy, this is the last biotic frontier, housing nearly 50 per cent of the biodiversity of terrestrial ecosystems. As she speaks Devy gobbles words in her excitement, till the conversation dissolves into adjectives and barely discernible fact.
A study in 2004 of the arthropods (insects, spiders, etc.) in two species of trees in the Western Ghats found 219 and 372 species on them respectively; of which there were an astounding 31 species of ants.
The canopy is also the
interface between 90 per cent of the earth’s biomass and the atmosphere,
regulating global temperature gradients, precipitation and airflow. Canopies
have been explored in other parts of the world over the last few decades.
Working in the forests of Panama, entomologist Terry Erwin discovered over
1,000 species of insects on a single tree, and 1,200 species of beetles on a
cluster of trees of a single species. This finding shocked biologists,
kick-started canopy studies, and led to a major revision of
biodiversity statistics.
Biologists working in Malaysia discovered that the towering 70-metre-tall dipterocarp trees were pollinated by minute insects less than a tenth of a centimetre in length; in Costa Rica they found that canopy trees put out a secondary system of roots that taps the thick layer of organic matter that accumulates on their branches.
In work that has ramifications for climate research, Meg Lowman, the world’s leading canopy expert, showed forest foliage had been severely underestimated by previous ground based studies. Leaves in the canopy, she found, could live anywhere between four and 10 years. It now emerges that 60-90 per cent of animal species and 50 per cent of plant species in tropical forests live in the upper reaches of large trees.
In India however, canopies are just beginning to be understood. Studies have so far focused on inventories of the phenomenal biodiversity of these upper reaches.
Much more remains to be done on their complex interactions.
The predominant tree species here are Cullenia exarillata (wild durian), Aglaia bourdillonii, and Palaquium ellipticum (also known as Palai). With an average height of 30 metres, these trees form the bulk of the canopy, overshadowing other common species like bitter nutmeg (Myristica dactyloides).
In the 1970s, parts of these forests were opened up for plantations and timber extraction, both later abandoned. As a result the present forests are a patchwork of untouched forest interspersed with forests where trees of certain species were selectively removed, and patches that were clear-felled. These forests have regenerated to varying degrees, giving researchers a glimpse into how varying levels of forest disturbance affects species.
“When we started out people told us we were crazy,” says Devy, with a wide gentle smile that makes her look more like the neighbourhood Betty Crocker mom than an intrepid explorer. The work was dangerous, with little safety equipment. They ascended trees using a system of steps used by the tribal Kani honey collectors of these forests. These rickety steps were made of poles hammered onto the trunk and branches. Climbing up them was tedious, “risky business,” Devy says. “But every pioneer goes through this.”
The first forays opened up a new world—one that has occupied Devy, Ganesh, other scientists and a whole generation of students like Ramachandran, who have followed in their tracks.
Vivek Ramachandran’s interest in canopies was sparked by the work he’d done on the endangered Narcondam hornbill of the Andamans. His first ascents into the canopy revealed the sheer enigma of this ecosystem.
By the time he started researching canopies in 2005, new techniques and technologies had made things easier. The tree steps of the Kanis had been replaced by the single rope technique (SRT), borrowed from rock climbing. It uses a single length of rope climbed with the help of friction hitches. While this limited the climber to vertical movement, the addition of another rope to the ensemble allowed for horizontal movement. These techniques made it faster and much safer to climb trees.
Also gone were the bulky film cameras that Ganesh used for camera traps in the canopy. Installing them was painful; the camera had to be placed at such an angle that it was not triggered by near-horizontal morning and evening light. Despite these precautions, false triggers often resulted in the camera using up entire rolls of film in a few seconds, with shot upon shot of branches. Now, with digital recorders and video cameras, photography is less painful.
Ramachandran started looking at the birds and small mammals that live in the canopy. The forests of KMTR are not as “vertically differentiated” as forests in South and Central America. Yet they can be divided into layers: the “over-storey” that consists of the crowns of a few trees that soar above the canopy; the canopy, a dense ceiling of close trees; the “mid-storey”, sparser branches that lie beneath that; and the “under-storey” that extends down to the ground. Were different species of birds and mammals found at different heights, he wondered? What kept them in these zones?
The work was painstaking. Trapping small mammals on the ground, and at different heights in the canopy—the whole top strata—required setting up a grid of traps. On the ground the grid consisted of nine parallel trap lines, 10 metres apart from each other. Each trap line in turn had seven traps placed 20 metres apart. The arboreal trap line within each of these grids consisted of traps set at four different heights, from the ground to the canopy.
In all, 104 traps, baited with grated coconut and bitter nutmeg seeds, were sampled over a period of five days. The sampling, spread over seven different cycles between December 2006 and May 2009, was also done in disturbed forest patches. This allowed Ramachandran to assess the effects of tree-felling on small mammals.
What he discovered was surprising. The most common creature, the Malabar spiny dormouse (also known as the “pepper rat” since it’s found in pepper plantations), was the one that previous ground-based sampling had labelled “elusive”. This creature with the body of a rat and the tail of squirrel (which it uses as a counterweight when jumping from branch to branch) was found exclusively in traps in the canopy and the mid-storey. As were two other fruit-eating squirrels: the dusky palm squirrel, a uniformly brown squirrel, and the jungle striped squirrel. These creatures seemed rarely ever to come down to the ground.
The rather unremarkable white-bellied wood rat, the second most common mammal, dominated the ground. There seemed to be a clear segregation between it and the dormouse, which Ramachandran suspects might be a strategy to avoid competition for resources.
Birds in the canopy were, however, as abundant as small mammals were few. Cataloguing them required the erection of 18 canopy platforms at an average height of 25 metres. The platforms were located a minimum of a kilometre from each other to reduce the chances of the same species being counted repeatedly. Birds were counted from each platform and the forest floor beneath it, between 6.30 a.m. and 6 p.m. on two consecutive days.
For Ramachandran, “the challenge and the greatest excitement of this work was that it was something that had not been done in South Asia before.” The 2,578 bird sightings sorted into 59 species.
He found that birds fell into four different guilds. Those that fed on nectar and fruit, like the black bulbul, the rare mountain imperial pigeon, and the electric green, pink-violet and yellow crimson-backed sunbird, largely inhabited the upper canopies where their food was abundant. These birds also preferred the relative dryness and the high light levels of the canopy.
Insectivores and carnivorous birds seemed uniform in their vertical distribution. Some like the babblers preferred the relative coolness close to the ground. Birds like the orange-headed thrush that ferret around fallen leaves for insects also stayed close to the ground.
Others like the brightly coloured Malabar trogon, a few species of flycatchers, racket-tailed drongos, and woodpeckers were found in a wide mid-storey band. These birds required a broad foraging band to meet their requirements. On the other hand, birds of the under-storey and canopy occupied narrower vertical strata since their food sources were more localised.
Curiously, the heights they occupied depended on how they fed: whether they caught their insect prey in flight, or sitting on a branch; whether they “leaf gleaned”, plucking insects from leaves, or waited for them to fly off leaves before catching them.
Birds like the grey-headed canary flycatcher—a shocking yellow little bird that catches its prey mid-flight and so finds it difficult to operate very close to the ground—were only found above the lower mid-storey.
Woodpeckers and warblers that leaf gleaned were found primarily in the mid-storey where the foliage density was the highest.
Nine species were detected exclusively in the canopy and 16 were more abundant in it; while the under-storey had 11 unique species and more frequent sightings of eight species.
As in the case of mammals, ground-based sampling had revealed little of this complex stratification in forest canopies. It had also, across the board, underestimated the abundance of species.
But despite the time Ramachandran spent in the trees, the canopy was slow to give up its secrets. One day while working 32 metres up in a canopy, he put his hand on a branch to find it on a tiny Rhacophorus tree frog. The frog, which has strong webbing between its elongated toes, jumped right off and glided into the foliage below.
“It’s often impossible to spot creatures unless you’re looking specifically for them,” so dense is the canopy, he says. “There have even been sightings of the king cobra in the canopy. This work gave me a completely different perspective, showing how dependent certain species are on particular niches within habitats.”
This complexity in forests that Ramachandran characterises as “species poor” is a pointer to the discoveries to be made in the forests of northeast India, which “have three times the species diversity of the Western Ghats”. But first he’s planning to explore the canopies of the Andamans.
***
The incredible bird
diversity of the canopies is sustained by an even greater, largely undiscovered
diversity of spiders, beetles, flies, butterflies, ants and other insects that
courses along these aerial walkways. A handful of researchers have been
capturing them, studying how they’ve adapted to arboreal life.
Priyadarsanan Dharma Rajan of ATREE started out as a casual collector but was soon hooked. The canopy was teeming with wasps and sap-sucking insects, while the ground below was rich in flies. One of his first discoveries was a grasshopper that lives 25-30 metres up in the canopy, the only known relative of which is found in the Americas. This specimen has still not been classified, and is currently with a taxonomist in China.
Next he stumbled upon a species of ant, Vombisidris humboltdicola, found only on Humboldtia, an under-storey tree. The leaves of the tree have tiny chambers at the base to house the ants, and the tree even has modified organs called extrafloral nectaries on leaves that secrete nectar for them. Of the 12 known species of this ant family, this was the only other to be found in India, with the rest found largely in southeast Asia. In return for food and shelter, the ants, it is thought, protect Humboldtia from the ravages of other creatures.
Very soon, Dharma Rajan realised parasitic insects were perhaps the best indicator of the canopy’s insect diversity. Of the more than 20 species of Ficus found in these forests, each had its own set of five to 10 pollinators, and each of these were preyed upon by their own set of parasitic insects that laid eggs in their larvae. In one family of parasitic wasps, Ichneumon wasps, he found 55 different species, of which 35 were new to science.
But classifying these new species is difficult. There are so many species in the canopy and so few that have been described, so classification “might take a few more decades,” he says. Even for species like ants, with lower diversity, there is little baseline data on numbers, habitats and habits. For the last decade he’s been working on beetles in the canopy, of which there are 30,000 species.
But how does the insect diversity of the canopy compare with that of the ground? Devy and a few collaborators set out to address this in a recent study. They took 60 samples from small patches of epiphytes (plants that grow on trees) on Cullenia exarillata and compared them to samples taken from patches of similar size on the ground.
They found that on an average the canopy had 1.7 times more invertebrates (ants, beetles, spiders, etc.) than the ground. The life cycles of many seemed tied to the canopy. Some of these insects originated from the forest floor or streams where they fed as larvae, before moving up the trees. They were a steady source of food for predators like spiders during the winter.
The team also found some unique adaptations—some beetles had specialised feet for walking on leaves, while others had bristles on their feet that helped them slow down on landing from a flight. Most had evolved varying degrees of camouflage to evade birds, lizards and frogs.
The team also found
some unique adaptations—some beetles had specialised feet for walking on
leaves, while others had bristles on their feet that helped them slow down on
landing from a flight. Most had evolved varying degrees of camouflage to evade
birds, lizards and frogs.
“The upper canopy is an extraordinary strata,” concurs Y. B. Srinivasa, till recently with the Institute of Wood Science and Technology in Bangalore. “It is a separate biota for conservation.”
Srinivasa’s first forays into the canopy in 2003 were in search of beetles, spiders, scorpions and tiny sap-sucking insects called leafhoppers. He was based in Coorg, north of KMTR, where the main forest canopy trees are Vateria indica (Indian copal) and Dipterocarpus indicus, both very tall trees that can reach heights of 60 metres. In forests of this height the lowermost branches often appear as much as 25 metres above ground.
After ascending the trees, heavy equipment in tow, he’d fog the canopies with a mild insecticide. In about 20 minutes the insecticide would knock out his prey and they rained down on to sheets spread below. It was arduous work, but every season had its surprises.
“Before and during the
monsoon there is a proliferation of flies,” he says enthusiastically, “a
fantastic diversity probably recorded nowhere else in the world.” Post-monsoon
caterpillars carpet the branches, and parasitic wasps emerge to feed on them.
This is also the time cockroaches, “millions of them”, appear. Srinivasa hasn’t
seen such a range of them on the ground, and believes that most never come
down. A Dipterocarpus canopy that he fogged yielded 19
different species of ants, and 160 flies belonging to 114
different species.
But his most exciting discovery has been of a canopy-dwelling scorpion belonging to a group known as Isometrus. This species does not resemble any of the other 13 Isometrusspecies known from India. It’s light brown in colour—to meld with tree branches, and its front limbs are thin—for pulling out prey from under the bark.
“Its body is not designed for life on the ground,” Srinivasa says. In contrast, a relative from the same genus that lives on the ground is darker and has strong front limbs for digging. Fogging brought down 13 individuals of this (yet unnamed) species of which some were juveniles, leading Srinivasa to surmise that the entire life cycle of the scorpion is spent in the canopy.
The spiders of the canopy—54 species were found in the fogging samples—use camouflage to overcome the paucity of hiding spaces. “Take those found on the ground and those from the canopy in two petri dishes,” explains Srinivasa, “you’ll find the ground spiders to be brown or black, and those from the canopy either pinkish, white or yellow.”
Of the 54 species, 14 were seen for the first time in India, and he suspects 11 might be new. More samples are needed to corroborate that since many specimens are damaged during their fall from the canopy or are juveniles, making identification difficult.
In 2004, in one of the first studies of its kind in India, Srinivasa and a few colleagues set out to inventory the insect diversity of Vateria indica and Dipterocarpus indicus. They found an astonishing 219 species in the former and 372 in the latter. Ants from 31 species accounted for a third of the specimens collected. As species diversity goes, Srinivasa thinks it is comparable to the Amazon.
“We take credit for quantifying the diversity of the upper canopy in India,” he says, with the tone of a man not prone to excess modesty. But for now, it seems the magnitude of the task and the lack of support have defeated him. “Hardly anyone is interested in flies,” he sighs.
His collection of cockroaches has been gathering dust; seven years on, his scorpion has still not been taxonomically classified; and he’s donated his collection of ants.
If he had a chance though, he’d like to study the behavioural adaptations of the canopy. Like that of a particular ant described in the journal Nature, he says, the enthusiasm back in his voice, “which jumps off branches and falls all the way to the ground”.
Given the rigours of work in the canopy, the lack of funding, and the methodological thoroughness that scientific studies need, it’s not surprising that most biologists focus on just a few species. In the absence of a broader canopy monitoring programme in India, this means that interconnections between the species are not explored fully. Often they emerge only when the work of these scientists is juxtaposed.
Butterflies and dragonflies have been the focus of Anoop Das, a zoology professor at a Kerala college. The aim of his butterfly study was to compare their diversity in canopies with that in forest edges, gaps where trees had fallen, and shaded areas. His study in the Silent Valley National Park in Kerala used long mesh cylinders hoisted up into the canopies to trap butterflies. The bait—mashed pineapple, rotting bananas, and a liberal dose of rum—lay in a container at the base. Twenty-four traps were installed in different locations; to be brought down after 10 hours each day.
They netted 3,021 individuals belonging to 35 species. Canopy species turned out to be very different from those found on the edges of forests: areas that are more open yet being closer the ground, more sheltered. Some species, like those of the skipper family of drab, moth-like butterflies, were found only in canopy traps, leading Das to surmise that they fed on rotting fruit lodged in the upper branches.
He also discovered an elegant red-yellow-black dragonfly, Lyriothemis tricolor, that breeds in water collected in tree holes.
Crickets in the canopy, more specifically their calls, caught Manjari Jain’s fancy. First, using acoustic sampling that required dangling recorders, laptops and researchers from the canopy, she tried to pinpoint the different microhabitats that crickets were using within the canopy. The distinctive calls of each species allowed her to hone in on their locations—of the 13 species examined 10 showed preferences for certain niches.
One species called exclusively from the trunks of large trees, another preferred a rarer habitat: dead rotting logs. Two were canopy specialists, three (one called Brochopepluslooks like a folded leaf) called from the under-storey, while one species was found exclusively in brambles.
Next Jain wondered whether their calls fitted in with a common hypothesis in animal acoustics, that signals and calls evolve in response to constraints imposed by the habitat. These constraints like distance and density of vegetation affect acoustics. If this hypothesis held, crickets would be calling from places best suited to the transmission of their calls.
Unfortunately for her, crickets call exclusively at night. That meant long nights up in the canopy shining torches in the direction of calls in the hope of spotting the movement of their long antennae.
The hypothesis did not seem to hold. Crickets often called from locations in the canopy that were extremely bad for call transmission. Of the two species that called from the canopy, one had a high frequency call while the other had a very low frequency.
Some species calling from different heights had overlapping call frequencies. It appeared that niches weren’t determined by acoustic competition but rather by other factors, like resources and predators.
***
What was sustaining
this incredible menagerie of insects in the canopy? Not all of them fed on
fruit, so where did they find their food? The canopy is also fairly
inhospitable, with few places to shelter, so where did they live?
These are questions Soubadra Devy started answering in 1990 after finishing her masters in ecology from Pondicherry University. She was interested in monitoring epiphytes—plants like orchids, ferns and mosses that grow non-parasitically on trees, deriving moisture and nutrients from detritus and the atmosphere. In the lush evergreen forest of KMTR, these plants start appearing at the level of the first branches, extending all the way up into the canopy. Trees often drip tangles of these plants, so intertwined that they look like one giant creeper.
The roots of these masses of epiphytes form a tangled web that can extend anywhere between three and five metres along branches. It captures leaf litter, fallen flowers, and other detritus to form a thick nutrient bank. These “epiphytic root mats” are the aerial soil and anchor on which new epiphytes grow, and the thousands of insects that biologists have discovered in the canopy find shelter and food. Some of these mats grow so large and extensive that they can weigh more than 200 kilograms.
Earlier, epiphytes had only been sampled from the ground, when they fell or were dislodged by animals. But now using the single rope technique it was possible to track them in situ.
It was a revelation for R. Ganesan of ATREE, a student of Devy’s, who had looked up yearningly from the ground at the mass of colour above. Orchids like Bulbophyllum elongatum—so called because of the cactus-like bulge at the base of its leaves that stores water for use in dry windswept canopies—flowered in August during the ephemeral dry period between the two monsoons. As did B. fischeri and Eria reticosa with its five-pointed, star-shaped white flowers.
Thirty of the 58 species of orchids found in these forests were epiphytic. Fagraea ceilanica, with large, yellow funnel-shaped flowers, started life as an epiphyte but then grew roots that crawled down the tree to anchor themselves in the ground.
The canopy, Ganesan found, also harbored Impatiens auriculata, one of the few members of the balsam family that grows as an epiphyte. This plant, with whorled red flowers, also has a succulent stem that it uses to store water during the rains; in summer it sheds its leaves and the stem becomes flaccid.
Epiphytic creepers trap leaf litter and dried flowers of their host trees to form sheets and mounds colonized by as many as 15 different species of plants. The whole ensemble cascaded down overhanging branches, like a green frozen waterfall.
In 1990, Devy, using her own resources, acquired three one-hectare plots in KMTR for the long-term monitoring of trees and the epiphytes they harbour. In these plots, 800 individual trees belonging to 60 species have been tracked like precious children since then. Twenty-five species (five specimens of each) are tracked even more intensively. Every five years, there’s a detailed census. Every flowering new growth is noted, and correlated with weather and rainfall measurements.
This is where K. S. Seshadri, a young biologist looking for a job, spent two years looking at the distribution of epiphytes. Some were found near the trunk, others were on branches further away. What determined their distribution? Did they have preference for particular trees?
Every day, Seshadri would take a bus into the forest. From the ground he would search for a tree that had at least five epiphytes. Then came the hard part—tossing the fishing line onto the tree—a process that could take anywhere from “10 minutes to 10 hours”. Four trees adjoining the one selected would also be sampled to look at any effect the presence of epiphytes on neighbouring trees might have.
He’d sample “two or three trees every day”, spending anywhere up to seven hours on one, finishing by 6 p.m. to take the bus back. “I lost 20 kilos in the process,” he laughs, his unruly, flouncy orb of hair effecting the air of a man-of-the-wilderness. “And I was lucky to avoid lightning, which strikes trees with remarkable frequency”.
He found that taller trees with longer branches had more epiphytes. Their height gave them a greater chance of capturing floating pollen and seeds. Some epiphytic orchids like Eria pauciflora, with its translucent and delicate white flowers, were found all the way from the trunk to the edges of branches, while a thin stick-like epiphyte that needed lots of light was only found on the fringes.
A total of 100 trees of eight different species were sampled. Between them, they harboured 17 different types of epiphytes. Fifteen species preferred Cullenia exarillata, the dominant (and tallest) tree in the forest. Seshadri thinks this preference is due to a combination of factors: the relative commonness of Cullenia, as also because of its dusty, flaky bark that gives epiphytes a good toehold.
Epiphytes on most trees were found on branches orienting upwards; and facing southeast-southwest. Branch girth and the presence of moss were the other factors that influenced their abundance.
In subsequent work, Devy has found that epiphytes transplanted up or down on the same tree tend to do badly. Changes in fog patterns in these forests also seem to have affected them adversely. Given this extreme sensitivity, and the fact that they’re the most exposed to any atmospheric changes, she thinks they’d serve as good bellwethers of climate change.
Another group of plants that supported insects and attracted large numbers of birds to the canopy were mistletoes, parasitic shrub-like plants. Their leaves mimic those of their hosts, and their nectar-laden flowers attract a cohort of birds.
In the KMTR forests, the most common mistletoe is Dendrophthoe falcata. Its finger-shaped, bright red-and-yellow tipped flowers look like hands, palms facing upwards. Birds like the Oriental white-eye (a small bird with eyes rimmed with white kohl), plain flowerpecker, and the small sunbird frequent the flowers, teasing them open to get to the nectar and in the process getting dusted with pollen.
This mistletoe shows a fascinating variation across the Western Ghats. In the southern areas it is found only in tall canopy trees like Palaquium and its flowers are bigger than elsewhere. A few hundred kilometres to the north the flowers shrink in size, and change colour ranging from pale pink to white.
Why this happens is not yet clear.
***
While the canopy and
the arboreal plants in it are home to all these creatures, the relationship is
symbiotic. In return for all that they get, they protect their host trees, and
more importantly, pollinate them.
To understand the mechanics of this process, Devy and her husband set about examining the pollination of Cullenia exarillata. This dominant species is like a key, one to which they’ve returned repeatedly for clues on unlocking the canopy’s myriad secrets.
Every year, from December to April, the tree produces brownish-yellow tubular flowers that cluster around terminal branches, making them look like giant bottle brushes. The fleshy base of the flowers, soaked with nectar, is what visitors come looking for.
To document these visitors, Devy and Ganesh set up camera traps facing these branches, 25 metres above ground. Each of 11 trees was observed continuously for seven days and nights. Ever hungry for more detail, they also examined flower parts that visitors tossed after they were done. This gave them clues as to their feeding styles, and whether they were likely to pollinate the tree.
For nocturnal animals,
this meant observations by torchlight. When bats were the pollinators, they had
to be captured in fine nets to facilitate
identification.
The cameras recorded several mammals visiting the flowers—lion-tailed macaque, Nilgiri langur, giant squirrel, Malabar spiny dormouse, dusky striped squirrel, and the brown palm civet; and two species of bat. These were interspersed by the visits of 16 species of birds, two species of bees, some butterflies, and a couple of ants, beetles and moths!
This detailed tracking showed that flowers were visited as frequently at night as they were during the day. But an examination of the fallen flowers, combined with observations of creatures feeding on the flowers seemed to suggest that only the lion-tailed macaque, the Nilgiri langur, and the two nocturnal bat species could be pollinators. None of the birds, bees or beetles got to the pollen that was deep down in the flower.
The next question was why this strategy of using two different sets of animals, one very social and the other solitary, evolved.
Looking at the other data they had, Devy and Ganesh realised that bats were infrequent visitors to the Kakachi forests of KMTR, restricted largely to the forest edges, and their appearance was seasonal. The trees needed a back-up. Primates were reliable and numerous even though they were not very efficient pollinators.
Next the duo set out on an even more ambitious study that Devy explains “looked at pollination from a resource perspective”. How did the availability of flowers at particular times of year determine which species would be the pollinators or even perhaps, shape their habits?
Most trees here, apart from Palaquium ellipticum and one or two other species, did not flower annually. How did this affect bees, significant pollinators in these forests?
Two species of bees—rock bees and cavity bees—pollinated nearly 16 different tree species. They had distinct life history traits: the former built large open hives on treetops or cliffs, and were long-distance migrants. Cavity bees on the other hand moved short distances and nested in small crevices and tree cavities, which limited the size of their colonies.
These differences led to interesting patterns: the annual flowering of Palaquium was tracked by rock bees which came in larger numbers, requiring high flower densities. They arrived on the trees around May and moved on after the flowering.
Cavity bees, however, given the smaller sizes of their colonies and restricted mobility, maintained a steady population through the year, utilising the staggered flowering of trees in the vicinity.
The team also discovered another interesting visitor. Every five years, Palaquium has a particularly rambunctious flowering, known as a “mass” flowering. It seemed that this was tracked by a particular species of fruit bat that, according to Devy, “flew long distances, coming from very low elevations for the event”. These bats manoeuvred leaves into tent-like structures open at the base where they nested. How did they know of the mass flowering? “I think they undertake scouting trips,” she says tentatively.
Devy holds that integrated studies like this one—looking at the habits of individual species through their complex interactions—are essential to understanding the canopy. “What we need desperately are studies that are from canopy to soil, examining the relationship of the canopies to all the strata in between.”
The complexity of the canopy is the fine balance of thousands of interactions, one that is also prone to easy disruption. Some of the effects of disturbances have been studied in the patchwork of clear-felled (and since somewhat regenerated), selective-logged, and pristine forests in KMTR.
In his work on small mammals and birds, Vivek Ramachandran found that in clear-felled patches, mid-storey birds like the Malabar trogon disappear completely. These species, which have broader vertical foraging requirements, find their food sources diminished. They are replaced by species from the canopy for whom the regenerating forests hold a proliferation of flowers and fruits; and those from the ground, which in these sparser forests move up in search of insects.
Different species of KMTR, including epiphytes, are affected to varying degrees, but this is an area that remains to be studied in greater detail.
Canopy studies in India have progressed painfully slowly in the absence of a larger canopy research programme. There has been little money, with dedicated researchers often ploughing in their own funds.
Canopy studies in India have progressed painfully slowly in the absence of a larger canopy research programme. There has been little money, with dedicated researchers often ploughing in their own funds. Most of the work has been done at ATREE under Devy’s guidance. The remainder has been done by enthusiastic individual researchers scattered across other institutions.
Each of them has, however, been limited to very specific aspects of the canopy, since most institutions don’t have the funds for projects with wider ambits.
“Neither does anyone give money for long term monitoring,” says Devy. But with increasing recognition for her work, Devy has managed to make some headway. The high point, she says, has been an international canopy conference that she managed to bring to Bangalore in 2009.
She says interest, especially among younger people, in canopy research is growing. Over the last year she’s tried to rope amateur biologists and citizen scientists into canopy research. A beginning has been made in Darjeeling and Sikkim.
But the biggest hindrance, canopy researchers concur, is red tape. A few years ago Ramachandran had driven the “entire length of the southern Western Ghats” to select sites for the installation of Whole Forest Observatories. These are comprehensive assemblages of canopy cranes (cranes adapted to permit horizontal access over canopies), animal traps, meteorological towers that monitor temperature and moisture at different levels in the forest etc. It’s the next best thing to moving a rainforest into a laboratory.
This project, backed by the Global Canopy Programme, an international alliance of research institutions and NGOs, had picked India over Madagascar, Ghana and China. After a lot of searching, seven sites in mid-elevation forests were selected, some of which were the Ranni Konni forests south of the Periyar Tiger Reserve, a part of the Anamalai Tiger Reserve, a site in Wayanad, and one in Nilambur, Kerala.
Unfortunately one of the criteria for site-selection was that they be in untouched forest patches. In India this meant they were in protected areas. According to Ramachandran, even though most stakeholders—state forest departments and local NGOs—were enthusiastic, the Ministry of Environment and Forests didn’t approve it on the grounds it would disturb the forests.
Even efforts to bring canopy cranes to India have failed, despite Devy now having the financial resources to do so. As a result, India has fallen behind its favourite benchmark, China, which has two, in canopy exploration.
***
Each day the forests
of KMTR continue to reveal secrets. As night descends another group of intrepid
researchers makes their way up the trees.
Nandini Rajamani Robin has been chasing flying squirrels, “mysterious creatures of the night”, for a decade and a half. Two species—the Indian giant flying squirrel and Travancore flying squirrel—are found in the Western Ghats. The former, she says, “can weigh up to three kilograms and is the size of a cat”. It even looks like a brown cat sitting up in trees she says, earning it the sobriquet of “mayapoonai” or flying cat in Tamil. To add to the aura of mystery, its call sounds like a baby wailing.
Its gliding technique is to jump off a high-branch and spread-eagle its legs, stretching the flaps of skin between them. “At night it’s incredible to hear it whoosh from tree to tree, gliding distances of up to 100 metres in open forests. It can even alter course mid-glide,” says Robin.
The Indian giant flying squirrel is entirely nocturnal spending, Robin discovered, most of the day in tree hollows to emerge at the “crack of dusk”. It almost never comes down to the ground, and subsists on a fairly indiscriminate diet of flowers, fruits and leaves. The only time, in all these years of research she’s ever found one on the ground was when one, afflicted by cataract, fell.
To find these elusive creatures, Robin and her team would walk late at night along small trails in the forest, pointing torches into the canopy to catch a squirrel’s “eye shine”. The squirrel wasn’t rare but not very common either; they encountered four every kilometre. To trap them they’d hoist traps baited with jackfruit leaves, 20 metres into the canopy.
Up in the trees, the squirrel seems quite content sharing its space with a variety of other creatures. On occasion it even shared hollows with a Malabar grey hornbill; while Robin has seen its smaller counterpart, the Travancore flying squirrel, on the same tree as a brown palm civet and a ratsnake. They do, however, have canopy predators: owls, lion-tailed macaques, and grey pied hornbills.
The Travancore flying squirrel is smaller, weighing only about half a kilogram, and is a fussier eater. It is much more limited in range and selective about its habitat, therefore rarer. In 2013, in probably the first study of its kind in India, Robin radio-collared one of them near the Periyar Tiger Reserve and followed it for nine months. “Many times even when we knew that the squirrel was over our heads, it was very difficult to spot,” she says.
In this nine month period, the squirrel, like a restless backpacker, changed 16 hollows. In one particularly peripatetic week, it skipped five hollows.
The only competition to the Indian giant squirrel in sheer surprise comes from its reptilian equivalent, the Western Ghats flying lizard. This lizard, little more than the length of a pencil, is so well-camouflaged that it looks for most parts like piece of bark. Its ability to glide, like that of the flying squirrels, comes from a membrane between its fore and hind legs. This ability is put to use most frequently during territorial fights when a male chases another up a tree till it glides away to another tree.
As night advances, a chorus of frogs rises in a crescendo. Seshadri, who’d been focussing on epiphytes in the canopy, came upon frogs entirely by chance.
One evening he was sitting up on a tree when it started raining. Soon he started hearing calls of a frog from somewhere up in the canopy. Without warning, a frog jumped off a branch, to disappear 30 metres below. His interest was piqued.
In 2009, on an equally dramatic stormy night, he chanced upon two new species of frog; and then in 2011 another one, christened the Kakachi bush frog. There clearly were canopy-dwelling frogs, but how many and of which species?
To find an answer he, along with T. Ganesh devised an automated call recording system using which they recorded frog calls in three different forest locations in KMTR during 2009-10. They found 10 species calling from the canopy, of which six were completely arboreal.
Of these, R. bobingeri, a green bush frog with the earnest look of an obedient child in a classroom, called the most frequently. It took Seshadri’s team a year to locate this tiny frog, half the size of a human thumb. The Kakachi bush frog called the least, possibly indicating fewer numbers.
Another interesting find was the Calacad gliding frog, which they found 32 metres up in the canopy. This frog wasn’t completely arboreal, descending to the ground to spawn.
Seshadri hopes to use frog vocalisations to monitor populations, and he’s planning to head back the coming monsoons to set up more recorders.
The work of this handful of researchers has, like a periscope, taken us above the familiarity of the ground, to give us a glimpse of a wonderful new world that is largely uncharted.
It’s a world at risk. “With climate change,” says Seshadri, “species are moving up. But for those that live in the canopy there is nowhere else to go.”
has worked with Outlook Traveller, Mint and Tehelka. He now freelances, and his latest hobby-horse is science journalism.
