Opening up the rainforest canopy to science
Modern rope access techniques combined with the latest technology are opening up the rainforest canopy and allowing ecologists to survey a much neglected area.
The rainforest canopy is only 30 to 50 metres up, yet because it is practically inaccessible and obscured by lower layers of foliage, it never receives anything close to the scientific scrutiny that it deserves. The rainforest canopy is where the trees gather light, photosynthesize and exchange gases. This zone harbours entire communities of animals and plants that live nowhere else.
For example, functionally important plant groups such as epiphytes, which provide important habitats for many vertebrates and invertebrates, reach their highest abundance and diversity in the mid and upper canopy zones more than 15m from the ground, are frequently under-represented in rainforest botany surveys.
Many species of invertebrate are canopy specialists and ecologically very important. Arboreal ants are astonishingly abundant and are the leading invertebrate predators of the canopy. They are also important secondary seed dispersers (many ‘ant garden’ epiphytes only grow in arboreal ant nests) and arboreal ants are also unexpectedly important herbivores.
Modern rope access techniques combined with new technology can yield valuable data for a reasonable amount of effort and cost
There are many other functionally important invertebrate groups that have members specialising in the canopy, including wasps (predators, parasitoids and pollinators), butterflies (pollinators and herbivores) and beetles (predators and herbivores). Many of these species are confined to the rainforest canopy.
It is not just small-sized invertebrate canopy dwellers that are eluding scientists in the canopy – big ones can go largely unnoticed as well. Most rainforests of the world include semi or permanently tree-living nocturnal mammalian predators weighing several kilos or more, such as many Felids, eg margays Leopardus weidi in the neotropics and the clouded leopard Neofelis nebulosa of southeast Asia; also Procyonids, eg cacomistle Bassariscus sumachristi of Central America, and the Viverrids of Africa and Asia, eg the linsang Prionodon linsang. Remarkably little is known about any of these beautiful canopy top predators.
Accessing the canopy
Although various techniques are available for accessing the canopy, none have really caught on and been routinely adopted by rainforest ecologists. One of the perceived problems in canopy research is that accessing the canopy is too expensive, or too time consuming, or requires too much specialist training, or simply does not yield sufficient data per unit effort to warrant the investment.
However, we believe that modern rope access techniques combined with new technology can yield valuable data for a reasonable amount of effort and cost. We will use two examples based on our own personal experience to illustrate this view.
The first example comes from a canopy epiphyte survey conducted in Zambia and the Democratic Republic of Congo in 2010; and the second example comes from a pilot camera trap survey carried out in 2011 in the rainforest canopy of Cusuco National Park, Honduras.
Epiphytes – plants that grow on other plants (usually trees) – are an important component of botanical and structural diversity in forests, and in some instances exceed the terrestrial plant diversity. Those in African rainforests have been especially under-represented in the scientific literature.
To address this, an expedition set out to conduct a preliminary survey on epiphytes on 40 mature trees located within two 1km2 woodland plots.
The canopies were reached using rope access techniques. These techniques consist of first shooting a throw line over a suitable high anchor branch with a catapult, then hauling over the climbing ropes and securing them, and then using climbing gear to ascend the ropes and move around in the crown of the tree.
There are various styles of climbing techniques and equipment, but in all cases the kit required is fairly light and can be easily carried to any tree that one wants to sample.
Over a period of 30 days two climbers managed to map epiphytes and collect samples from over 900 branches in the 40 sample trees. The resulting data gave a unique picture of the patterns of distribution and abundance of all epiphytes covering the sample trees.
For example, epiphytes showed strong responses to the aspect of different branches. Branches that received more solar exposure during midday had fewer epiphyte species than branches elsewhere. A similar trend was observed with their height in the tree, where many epiphytes avoided sites of excessive light exposure (eg the outer canopy) and were more abundant in medium exposed sites (ie the mid-canopy).
The kit required is fairly light and can be easily carried to any tree
All the kit required for rope access is relatively cheap, costing well under £1,000 including ropes. On the other hand, canopy ladders, walkways, balloons and platforms are very expensive (often in the order of many thousands of pounds), difficult to transport and limited in their spatial application.
Although rigorous botanical canopy surveys can be carried out cost-effectively with rope access techniques, it must be remembered that rope access techniques are physically challenging and that a fair amount of training is needed to become efficient and safe using the techniques. We believe the results are well worth the investment.
Camera trap survey
Surveying wildlife in the canopy has been mainly restricted to large animals that are easy to observe or hear in the day, such as many primate and bird species. However, smaller and more cryptic species, or nocturnal species including many species of Carnivore and Primate go largely unnoticed, and as yet there are no standardised survey techniques for such species.
To address this, we set up a pilot study using camera traps in the rainforest canopy of Cusuco National Park in Honduras. We used rope access techniques to place one camera trap high up (>25m) in a large strangler fig (Ficus sp), and two more camera traps in a fruiting tree, which we could not identify.
Each camera trap was left for 25 days. It took one afternoon to rig both trees and install the three cameras. All the camera traps (Bushnell TrophyCam) used passive infra-red sensors to detect animals passing in front of the camera, and were equipped with infra red LEDs to semi-covertly illuminate animals passing in front of the camera at night.
The camera in the fig tree was set to camera mode and the two in the other tree were set to video mode. The camera trap in the fig tree was triggered 50 times, and animals were visible in frame for 12 of these. The most commonly trapped animal was the kinkajou (Potos flavus – 8 out of 12 photos).
We also camera trapped a naked tailed climbing rat (Tylomys watsoni) – a new record for the Cusuco National Park in Honduras.
The two video camera traps in the other tree were triggered a total of 45 times (trap effort: 50 camera trap nights) exclusively by kinkajous over four different nights resulting in several minutes’ worth of interesting video. Improvements in camera placement will undoubtedly improve the hit rate, ie animal less likely to leave frame before the camera takes a picture.
Camera traps are getting cheaper all the time – the cameras we used cost around £100 each. More expensive camera traps (eg Reconyx Hyper Fire) have quicker reaction times (ca. 0.2 seconds) and will also improve hit rate. All these models are light and easy to transport.
The take home message is that the combined technique of rope access and placement of camera traps can yield lots of data for a reasonable amount of money and effort. I expect the next few years are going to turn up some interesting surprises and some amazing imagery from up there in the canopy. Watch this space!