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Speaker: Professor Francis Halle, renowned French botanist and Botany Professor Emeritus of the University of Montpellier

The three dimensional branching of a young tree is never uncertain or random, on the contrary, it is controlled by a genetic programme called an “architectural model”. To help us understand this programme and identify a tree’s architectural model, one has to take into account different units of growth and give an appropriate answer to the following three questions:

1) in the crown, are all the leafy shoots growing horizontally, or vertically, or is there a mixture of vertical and horizontal leafy-shoots?
2) on the trunk, are the branches regularly distributed, like in a Coffee-tree, or in whorls, like in a Pine-tree?
3) on the leafy shoots, are the sexual organs – either flowers, cones or sporangia – terminal or lateral?

To identify the “architectural model” of a young tree is not more than a first step. To analyse the 3-D form of mature large trees, the concept of “reiteration” is needed. Without reiteration, a tree remains unitary, as it is the case of archaic groups of plants – fossil trees, tree-ferns, Cycas, Araucaria, Palms, etc. Reiteration is a modern mechanism which allows a tree to become a colony. Modern trees are colonies, they are much bigger than unitary trees, and they have a much longer life-span with some tree-colonies becoming virtually immortal.

Francis Hallé is a professor of botany at the University of Montpellier, France. As a co-founder of the famous Radeau des Cimes canopy raft and leader of its expeditions until 2001, he has dedicated his life to researching tropical plants, particularly low-altitude rain forests, and carried out eight missions to study the canopy of equatorial forests. He is a pioneer in exploring life in the treetops of tropical forests, using a blimp-borne inflatable raft that rests on the tops of the trees of the canopy. “The rainforest canopy is still a largely undiscovered layer of the planet. Francis Halle’s pioneering treetop expeditions are carrying out vital research into what makes the world’s rainforests tick” (Gil Gillespie, Frontiers, 1998)

To read more about Prof Hallé and his inspiration for the documentary film “Il était une fôret” (Once upon a forest) which tells the story of how a primary forest is born, please see http://www.bbc.co.uk/news/science-environment-24904781 and http://www.bbc.co.uk/news/science-environment-24904781