Tropical rain forests have been a source of boundless fascination and discovery for as long as people have been exploring them. From Victorian naturalists like Wallace and Darwin who found their inspiration for theories of natural selection, to the latest advances in medicines and climate change mitigation, rain forests have revealed countless key insights to the workings of our natural world. Despite this however, there remain vast ecosystems that we have yet to study in depth and the largest of these is surely the canopy.
Aside from the deep ocean, the rainforest canopy is probably the least studied natural ecosystem on the planet and the reason why is obvious: those trees can be over one hundred metres tall! Because of this, getting to the top of them is understandably tricky and it wasn’t until fairly recently that the skills of climbing and academia came together and the field of canopy research took off. Before that, most studies of canopy species relied on either smoking them out of the tree or shooting them down with a rifle.
People have been climbing trees in the tropics for many years of course and there are even communities like the Korowai in Papua who live in villages amongst the tree tops. The progress of western science towards an exploration of the canopy has largely taken a separate approach from local methods however, with Sir Francis Drake (anecdotally) becoming the first European to summit a tropical canopy in 1573. The story tells us he marched four days inland in Panama to a tree where steps had been cut so that he might climb up and spy his enemy’s ships. This gained him a tactical advantage in battle and, perhaps more importantly, afforded his first view of the Pacific, reportedly inspiring his later circumnavigation of the globe.
Three hundred and fifty years after that, in 1929, a team of scientists from Oxford University began the first scientific climb to study the rainforest canopy in Guyana. The tree had to be climbed first by locals with spiked boots to attach ropes for them which would allow the scientists’ ascent to be made from the comfort of a suspended armchair (Hingston, 1930). The results of this research were enlightening and showed vast promise for the beginning of a new field. It was however not until the sixties that more studies of the canopy started to emerge in the scientific literature, as a Dutch expedition to Zaire constructed platforms from which to observe monkey behaviour and an American in Malaysia built an eight storey high ladder to reach his own research goals in the canopy…
Fast-forward another sixty years and you might wonder what’s changed when it comes to my own canopy expeditions. For a start, I am sadly bereft of comfortable armchairs from which to observe the goings on of the rain forest and I certainly try to avoid using ladders too. Instead, everything is streamlined to be light-weight, portable, and as safe as is reasonably possible. This all means I can climb faster, with fewer assistants, and cover more ground in each day. The result is a drastic increase in spatial data, allowing me to build a far more comprehensive view of the canopy ecosystem than past groups who have used complex contraptions with limited mobility. While I take the minimalist route to the canopy though, other researchers still build platforms and high-tech cranes which allow them to more comprehensively monitor a much smaller area. In the end, it’s all really cool stuff and we need every bit of data we can gather!
In this treetop world of staggering complexity and so many unanswered questions, it can sometimes be difficult to narrow one’s focus to a single point of interest but, for me, I can think of nothing quite so fascinating as the epiphytes.
Epiphytes are plants that spend their whole lives in the canopy. They are completely isolated from the ground throughout their entire life cycles and are utterly vital to the continued functioning of rainforest ecosystems. Without their ability to store water in the treetops after rainfall, many animals would regularly have to put themselves at risk from predators by making the long and tiring climb down to the forest floor to drink. Some species of epiphyte are known to hold so much water that they can even host frogs in the canopy too, without the need for grounded pools. Their use to the ecosystem goes beyond just water though; they provide habitats for insects who act in defence of their host trees and they produce food enough to supply up to a third of all bird foraging in some regions of the tropics (Nadkarni & Matelson, 1989).
The value of epiphytes is seemingly endless and yet we still know remarkably little about them around the world. The vast majority of our understanding comes from a few sites in South and Central America while other regions remain relatively unstudied (Barker & Pinard, 2001). Often, all we really know about epiphytes is that they are important and threatened by forest disturbance through human activities. How though, are we supposed to prioritise their conservation when we can’t know exactly where they are most diverse without long and expensive climbing campaigns to observe them? The answer is: by observing the trees on which they grow and improving our understanding of the epiphyte-host relationship to predict their distributions.
As a masters student, I took it upon myself to explore these host relationships on the island of Buton, in Indonesia, where forest is mostly threatened by local degradation and mining efforts. I wanted to know what the ideal host would look like from the ground. That way those trees could be protected as a precaution for the safety of canopy ecology without the need to check every individual’s value.
For almost two months, I carried hundreds of metres of rope into the forest with Ben and Asinu, my friends and colleagues who had each an expertise in climbing and forest survival. Together we used catapults to launch our climbing gear into the trees and provide us access to the canopy fifty metres above our heads. Slowly, making sure to watch out for the spiked vines and angry insects whom we were likely to disturb with our presence, we hauled ourselves skywards.
Inch by inch as we ascend the rope to the canopy, the rainforest vista becomes more and more impressive. Eventually, and if the tree is tall enough, you can see as a bird might, right the way to the island’s coast in one direction and across to rolling hills of forest in the other. Beneath, you can feel the living sway of the tree as it bends with the wind and in that moment it is hard to not be awed by this hidden world so high above our usual focus as humans.
After some time of simply enjoying the canopy, it always came time to take notes and complete our research. We tried our best to identify each epiphyte we could see (sorting by shape and characters when we couldn’t determine their names) and we measured their height, size, and location on the branch. Back on the ground, we measured the tree itself. Everything that was available to us, we tried to record. From the texture of the bark, to the diameter of the trunk and the area shadowed by its branches, we thoroughly classified each tree. We also drank a lot of water and reapplied sunscreen because working at height in the direct sun of the tropics is thirsty work!
After a great deal more work, this time under the glare of computer screens instead of the Indonesian sun, all this climbing resulted in the publication of my first academic paper in the Journal of Tropical Ecology (Hayward, 2017). We found through models of our different measurements that tree size was by far the greatest indicator that a tree would be host to a high diversity of epiphytes. The other properties of individual trees were largely meaningless, with even the texture of the bark (something we had assumed would be important for determining how easily an epiphyte could grip the branch) having no significant effect.
This is just one conclusion amongst the growing body of research on epiphytes and canopy ecology in a field of study that continues to reveal exciting and unexpected ecologies. New climbing techniques continue to be innovated and now drones, mounted with high quality cameras, are on the verge of revolutionising data collection in the field. With more information available to us than ever before, I feel certain that in time the canopy will be recognised as just as valuable a conservation focus as the systems of the forest floor. I look forward to uncovering more of its secrets.
This post was originally published with additional editing and review via Forest Ecology
Barker M.G., Pinard M.A. (2001) Forest canopy research: sampling problems, and some solutions. In: Linsenmair K.E., Davis A.J., Fiala B., Speight M.R. (eds) Tropical Forest Canopies: Ecology and Management. Forestry Sciences, vol 69. Springer, Dordrecht
Hayward, R., Martin, T., Utteridge, T., Mustari, A., & Marshall, A. (2017). Are neotropical predictors of forest epiphyte–host relationships consistent in Indonesia? Journal of Tropical Ecology, 33(2), 178-182. doi:10.1017/S0266467416000626
Hingston, R. (1930). The Oxford University Expedition to British Guiana. The Geographical Journal, 76(1), 1-20. doi:10.2307/1784676
Nadkarni, N., & Matelson, T. (1989). Bird Use of Epiphyte Resources in Neotropical Trees. The Condor, 91(4), 891-907. doi:10.2307/1368074