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Francis Hallé has proposed that the concentration and diversity of secondary compounds, many with biological activity, should be elevated in the rainforest canopy where herbivory pressure is the greatest and light might promote certain biochemical pathways. This is certainly a logical idea, given what we know about patterns of herbivory, and it has extremely important implications for biodiversity/ medicinal compound prospecting. Most of the search for new medicines occurs in the understory where it is more easy to collect the plants. Kelsey Downum and I participated in the French rainforest canopy expedition at La Makande, Gabon in February-March of 1999. We collected multiple leaf samples of four common tree species, from the understory and canopy, and are in the process of analyzing the secondary chemistry at this time. Some of the samples were sent to the Laboratory of Gary Towers at the University of British Columbia for bioassays. We have analyzed the four species for diversity and concentration of aromatic compounds by HPLC, and have found support for the hypothesis. We also worked with Martin Quirke of the Department of Chemistry to compare the diversity and levels of nitrogenous compounds, using the technique of electron spray mass spectrometry. We’re not certain how to continue this work, as we will miss the Madagascar expedition for autumn of 2001, perhaps the following expedition in Brazil.
Dirigible with luge (collecting sledge) on canopy foraging expedition,
La Makande, Gabon, March 1999.
On left is helium balloon tethered to line transect for very economical
access to rainforest canopy.
View of La Makande Creek and forest canopy, taken from luge.
Return of dirigible, deposited luge with collected material, after
early morning flight.
La Makande, Gabon in March of 1999.