Cauliflorous Feast: Chalmugra's Secret Life in Pakke Tiger Reserve

In January, on a cold morning in Pakke Tiger Reserve, I was walking through the forest along Khari nala trails with my field collaborator. Suddenly, I found a tree with fruits larger than my palm and brown in color. These fruits were growing along the trunk, from the canopy downwards, on every branch of the tree in large numbers. One can't miss it because it is so huge, with so many fruits, and also it is uncommon to see so many fruits along the trunks. Botanically, this phenomenon is called ‘cauliflorous’ fruiting.

As an ecologist working on seed dispersal in a forest, I generally examine plants through their fruits. Seeing so many large fruits makes me excited and my first instinct is to classify the fruits based on what animals might eat them, considering their size, colour, smell, and nature (whether fleshy or not). In this case, I already got a hint from the morphology of these fruits that something interesting happens here: the fruits are so big that no frugivorous animals have jaws or beaks large enough to engulf them. Additionally, there are so many fruits that numerous frugivores might share this resource. The fruits are also dull brown in colour and should have a smell to indicate ripeness to their consumers, but I still couldn’t detect any scent in February.

Curious, I asked one of the front-line staff of Pakke Tiger Reserve about these fruits. He told me excitedly that, locally, they are called ‘Chalmugra’ or ‘Hooka.’ During the fruiting season, hunters gather around this tree to hunt civets, knowing that civets will come to consume the fruits. This is exciting, but civets are nocturnal. How do they figure out if the fruit is ripe until there is a scent? I tried to pluck a fruit from the trunk to check its scent, but there was no smell and it was so tightly attached that we couldn't pluck it. My collaborator smirked and told me it was unripe. He said, “Until it is ripe, you can't pluck it with your bare hands”. I marveled at how intelligently the plant secures its most valuable possessions. Later, I got to know the scientific name of this plant is Gynocardia odorata.

I started searching online about their basic ecology, but I mostly found articles on the oil that can be made from its bark. So, I decided to study their interaction with fruit-eating animals thoroughly. Now, I have camera traps, which are the best devices to unravel these mysteries. I decided to place three camera traps on some of the fruiting trees, focusing on the fruits on the trunks, as these fruits were within our reach.

I went back to visit these trees after 20 days and noticed a jackfruit-like scent from 15 meters away. My field collaborator told me that the Chalmugra fruit had ripened. This time, I found that the previously unripe fruits had opened, with pulp and a few seeds that had fallen down, still wet, indicating that they might have been dropped the previous night while being eaten. I checked the camera trap footage and discovered some of the mysteries: civets and squirrels sniff the unripe fruits for days or weeks before deciding to bite into them. So, it appears that civets and squirrels can smell the unopened fruits when we can't. The best part is that once the fruits open, a variety of frugivorous animals gather until the pulp dries out or is finished. Civets come at night to swallow the seeds with fruit pulp after opening the fruit through biting, dropping many seeds in the process. Bats lick the pulp and carry the seeds away by holding them in their teeth. During the day, birds like thrushes and bulbuls enjoy the pulp, while rhesus macaques store the seeds in their cheek pouches and carry them away. Martens and squirrels also come to eat the fruit pulp, with squirrels often carrying the seeds further. Capped langurs generally consume unripe fruits.

When I checked below the tree, I found numerous hoof marks of deer and wild boar and many seeds ground to near powder in some places, likely the work of porcupines. Curious about what was happening below the tree, I set up camera traps and placed fruits and seeds in front of them. After 14 days, I returned to find more than half of the fruits on the trees had opened and been consumed, and there were no seeds below the tree. The camera traps revealed a feast below the tree: barking deer and sambar frequently visited to eat the seeds, while wild pigs occasionally came to eat large quantities of seeds too. Rats and mice carried seeds with pulp to cache them and sometimes ate the pulp in front of the camera traps. Martens came down to eat only the pulp, while porcupines meticulously feasted on the seeds. Occasionally, civets also swallowed pulpy seeds from below the trees.

In the meantime, while exploring the forests, I found many civet scats with seeds of this plant. I also discovered caches of these seeds hidden by murid rodents under dry leaves on the soil's upper layer. Squirrels eat the pulp and throw the seeds down, and rhesus macaques carry the seeds and spit them out. All of these animals act as seed dispersers. In contrast, sambar, barking deer, wild boar, and porcupines act as seed predators by preying on the seeds.

It is quite amazing how the fruiting of a single plant species attracts almost every mammal frugivore in the landscape to visit and consume its fruits. My camera trap footage on and below the tree suggests that this fruit brings a festival to every mammal frugivore’s lives, except for elephants. From small mammals like rats to large sambar, from canopy-dwelling common palm civets to terrestrial porcupines, from flying mammals like bats to birds like bulbuls, everyone pays tribute to its fruits by visiting, tasting, and consuming the pulp and seeds. After studying them, I now understand why civet hunters wait around this tree. I also realize that you cannot perceive everything in nature by yourself, such as the smell of unopened fruits. Through evolutionary selection processes, plants have developed important strategies like seed dispersal to be efficient enough for their seed dispersers only.

Our long-term data on fruiting phenology suggests that Chalmugra trees fruit every alternate year. This strategy might explain the bulk fruiting; the plant conserves energy by not fruiting annually and instead produces a large number of fruits every other year to enhance the efficacy of seed dispersal. Like other large, multi-seeded fruits, Chalmugra's pulp is attractive to a range of frugivores. Some of these animals disperse the seeds, some eat only the pulp, and others munch on the seeds, but whatever the fate of the seeds, these big brown cauliflorous fruits bring joy to their frugivorous partners by offering their pulp.