Magazine article UNESCO Courier

The Canopy Raft

Magazine article UNESCO Courier

The Canopy Raft

Article excerpt

SATELLITES, aircraft, ultra-light aircraft and tethered balloons all enable photographs and measurements to be taken from above the forest canopy. Something else is needed, however, for taking measurements and samples from within the canopy, hence the use of walkways and vertical towers at MAB research stations such as Sakaerat (Thailand), Tai (Ivory Coast), and DimonikaMayombe (Congo).

Another approach is to climb up into the canopy, either using the trunk as a means of support or directly into the branches from the ground or from a neighbouring tree. Abseiling is among the devices borrowed from rock-climbing that have been used in scaling up and down the forest profile, but this is definitely not a technique to be recommended to the unitiated or the fainthearted.

Recognition of the shortcomings of these methods led to the idea of using a hot air balloon as a method for studying the forest canopy. The idea was the brain-child of Francis Halle, a botanist who has long been interested in the architecture of tropical forest ecosystems, Dany Cleyet-Marrel, an aeronautic designer and owner of the balloon, and Gilles Ebersolt, a young balloon enthusiast and constructor.

The Radeau des Cimes (canopy raft), as it was baptized by its French inventors, is 31 metres long by 22 metres wide and con sists of inflatable rubber cylinders connected by a sort of net trampoline made of PVC-covered Kevlar. Weighing 750 kilograms, the raft serves as the nacelle for the hot air balloon of 3,000 cubic metres to which it is attached by twelve cables.

Once airborne, the raft skims downwind, just a few metres above the forest canopy. The two-man crew of pilot and scientist use a g uide-rope to orient the raft and to land it on top of the canopy. Once the raft is landed and secured, the balloon is deflated and folded away and the scientific work can begin. Liaison with a ground team is established by means of a caving cable, which enables other scientists to have access to the canopy.

Initial results have been promising. After trials with a helicopter-landed, 12 by 12 metre protoype raft in the Forest of Pilat, in France, in October 1985, the first field trails in the tropics took place in October 1986 in French Guyana, in the region of Montsinery. Samples were taken of trees, lianas and parasitic plants, which were then conserved using a method perfected by the British Museum of Natural History in London. Ultra-violet lamps and interception nets were among the methods used for collecting insects, particular emphasis being given to two groups of beetles. Other observations and sampling concerned epiphytic plants, ant gardens and atmospheric pollen.

If all goes well, a second set of trials, to be held in late 1987 at the MAB project site of Makokou, in Gabon, will seek to associate other scientific disciplines in addition to those that took part in the first series-medical entomology and parasitology, bioclimatology and mammalogy, ornithology and floral biology.

First, however, a number of improvements need to be made in the basic operation of the canopy raft. These include an increase in upward force, improvement of visibility through the nets, improvement of access from the soil, improvement of night use and the addition of a directional movement capability. At a post-trial meeting held in Paris in December 1986, the feeling was that these various improvements should all be technically feasible, although a fair amount of financial sponsorship would be required. …

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