Exploration of the rain forest canopy using airships and other methods
Why not simply climb trees without any complex devices?
If you only want to explore a few trees, its probably best to use the simplest and cheapest access technique: a single rope and climbing equipment. However if you want to explore hundreds of trees in days or weeks, this would very exhausting. Its also hard to get to the uppermost tree branches with single rope techniques.
What exactly is the canopy?
The canopy is defined here as the outer tree layer in the "bright zone" where important processes (such as pollination) take place - roughly speaking the upper 5 metres (15 feet) of the tree branches. Some biologists use broader definitions. Mark Moffett (1993) wrote: 'Purists claim that term canopy applies to the thin veneer of leaves struck by direct sunlight - the region of maximum photosynthesis, comparable to the ocean surface. To other biologists the canopy encompasses the crowns of these uppermost trees and the fan of limbs beneath the foilage. I use the term broadly to embrace the whole vegetation ocean beyond easy reach of ground dwellers, say from twenty or thirty feet up. This covers all the poorly know strata - including the middle (understory) levels'.
Moffett, M., The High Frontier, Exploring the Tropical Rainforest Canopy, Harvard University Press, 1993, see http://www.doctorbugs.com/writing.html
How many species of insect are there in rain forest canopy?
After sampling Panamanian trees in 1982 Terry Erwin, wrote a seminal paper in which he estimated there to be 30 million anthropods worldwide, far in excess of the previous estimate for the total number of species on Earth. Some experts disgree with Erwin's calculations, but most now agree previous estimates were far too low. We do know that samples from a single tree species can contain over 100,000 species of beetle (say), and there may be about 50,000 species of rain forest tree. See http://www.sei.org/terry.html and http://invertebrates.ifas.ufl.edu/ErwinRevised.pdf
What exactly is a dirigible and what is an airship?
A dirigible is steerable balloon, or a non-rigid airship. An airship is a general name for an aircraft that uses lighter-than-air gases (usually hydrogen, helium or heated air) to provide part or all of the lift force to balance its weight. Airships are usually divided into: rigid airships, semi-rigid airships and non-rigids. Rigid airships have a structural outer framework that is used to hold separate individual bags filled with lighter-than-air gas. Semi rigids usually have a long rigid keel structure. Non-rigids usually only have one gas bag and have no significant structure to support it. For a glossary of terms see, e.g., http://www.blimpinfo.com/glossary.html
Is it possible to use dirigibles to collect samples from the canopy?
Yes, this has been demonstrated in previous projects. The main challenge is holding the dirigible steady while collecting the sample when there are gusts of wind. To date samples have only been collected from the uppermost canopy in near still-air conditions, with a wind speed less than 1 metre per second. Future projects aim to demonstrate collection in moderate breezes and from lower canopy strata.
What is the likely wind speed above a tropical rain forest canopy?
Many measurements of wind speed have been made using anemometers mounted immediately above the canopy of various tropical forests. At some times in the year the average wind speed in most forests is not likely to exceed about 3 metres per second. The following link is an example of some measurements made in Amazonian forest: http://www.dendronautics.com/USERIMAGES/wind-probability.doc
What are the advantages (if any) of using a dirigible for canopy exploration as opose to using a crane?
Cranes are limited to a survey radius of about 50m. Admittedly this provides considerable scope since a circular area of this size might encompass about 800 trees, but some scientific questions depend on surveys over greater distances. For example, seed dispersal by birds can involve distances of over 20 km. Also some species of flora might not occur in the designated circle. It therefore makes sense to combine crane studies with the larger range studies that dirigibles permit.
What advantages do helium-filled dirigibles have over hot-air balloons and thermal airships?
Hot-air balloons (possibly retro-fitted with motors), and/or thermal airships both require a loud propane burner to heat the air within them and that would cause intermittent disturbance to the local environment - scattering fauna for miles around. They also have to be much larger to obtain the same lift force, and are consequently less manoeuvrable. Helium-filled airships have the potential advantages of being smaller and more agile (capable of getting into smaller canopy gaps) and they are absolutely quiet while drifting. The downside is that helium gas is not cheap, but canopy exploration deserves the best tools on offer.
Is it safe to use a helium dirigible/airship in close proximity to the canopy?
In still or light-air conditions it is possible to float about 2m from the tree branches, but in any conditions there will always be some random drift and there is a risk of collision with the trees and subsequent entanglement with the branches. It is therefore essential to carry abseiling equipment to permit the people onboard to descend to the ground without delay when necessary. The envelope or the hull must also be designed so that it cannot rupture badly. If proper procedures are followed, the safety risks are probably lower than climbing a rain forest tree with a single rope, because the strength of trees branches in the upper canopy is not quantifiable.
What happens if a storm grows while the dirigible is flying above the canopy?
It is essential to have proper meteorological reports concerning the likely atmospheric conditions prior to any flight. If there is any risk of strong winds, then no flight should be attempted. It should be noted that during storms tropical forest trees also sometimes fall - so standing on the ground in a tropical forest during a storm is not necessarily safe.
Given that canopy biologists have limited funds for their research, would it not be better to spend available funds on ground based projects, or projects that use practical low cost canopy access techniques?
If the canopy is as biodiverse as many eminent biologists have claimed, then the amount of funding for canopy research needs to be increased. The D4 airship was operated for 3 months at a fraction of the cost of some canopy crane projects. Helium costs are high, but petrol costs for similar timescale projects using 4WDs are also high! Airship platforms provide a cost effective method to access the upper reaches of a large number of trees over several kilometres. No other existing techniques are effectively competitive.