Information sharing

For four years, thirteen months of which were spent in the field in DRC, Jean Francois Bastin patiently increased his sampling data, benefitting from information-sharing by various international research institutions (CIRAD, IRD, CTFS, WCS, University of Yaounde, Oxford, etc.). In total, his database (more than 10,000 tree inventories in 175 parcels of one hectare) concerned four countries in Central Africa: Cameroon, Gabon, Central African Republic and DRC. In this enormous geographical area, he defined nine main zones that were carefully spaced out and which covered the main environmental gradients of the Congo basin.

The first conclusion of this work led to a basic observation: the structure of the tropical forest is stable. In order to properly understand this notion of “structure”, it is important to underline that this does not refer to plant varieties or species, but to the ratio between the number of large and small trees present. “It is necessary to imagine the forest in terms of volume”, explains the researcher. "Year after year, the forest fills up following the growth of trees. Whatever zone is being studied or whatever species is being considered, we noticed that the ratio between large and small trees is stable. In other words there is not a thousand different ways that ligneous vegetation can occupy space. Whatever their absolute size, larger individuals succeed in forming the canopy with their upper parts as they grow bigger. As they are large enough, they leave very little space for smaller individuals which, as they are a lot more numerous, fill the lower layers of the forest volume. But everywhere, the proportion between them is constant”.

A step in the right direction for Africa

These results are not completely surprising. They are directly in line with the theory known as the "Metabolic Theory of Ecology" (MTE). Designed by Professors West, Brown and Enquist in order to understand the structure of trees and forests (and published in Science in 1997), this theory suggested a model capable of characterising the invariant relationship between the size of trees and the number of individuals present. But, thanks to the uncertainties linked to bigger trees, its validity was a constant subject of debate between 2000 and 2010 and has even continued up to the present day albeit to a lesser extent.  

Jean-François Bastin and his colleagues used this model as a scientific starting point but with one difference: they focussed on large trees. They demonstrated that the ratio between large and small subjects is constant, thus supporting the theories resulting from the MTE. They were also the first to apply this theory in the context of their objective of simplifying carbon levels in the forests of central Africa, unambiguously showing the financial savings represented by the measurement of a minimal fraction of the forest environment. This represents an important step forward due to the fact that central Africa remains less well-known than the Amazon forest, both because of its political instability and the small amount of international scientific studies on the region (and which are also often written in French).