Sylvie Gourlet-Fleury et Jean-Louis Doucet : « Les forêts d’Afrique centrale ne sont pas uniformes »

published on 21 March 2022
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Forêts camerounaises
Aujourd’hui, la gestion forestière fait face à de multiples défis en termes d’adaptation au changement climatique, de préservation de la biodiversité et de durabilité de l’exploitation forestière. Si le plan d’aménagement est le premier outil de réponse pour une gestion durable des forêts, les pays d’Afrique centrale font face à un enjeu majeur : le renouvellement des stocks des espèces d’arbres exploitées. Pour Jean-Louis Doucet, professeur à Gembloux Agro-Bio Tech et Sylvie Gourlet-Fleury, chercheuse au Cirad, il est nécessaire de renforcer la durabilité de l’exploitation dans le cadre de l’aménagement forestier. A l’occasion de la journée internationale des forêts, ils nous parlent de leurs travaux dans le cadre des projets DynAfFor et P3FAC soutenus par le FFEM, et des recommandations qui en découlent, pour une meilleure gestion des forêts d’Afrique centrale
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Sylvie Gourlet-Fleury, researcher at Cirad and Jean-Louis Doucet, Professor at Gembloux Agro-Bio Tech

You’ve set up a data collection network on the Central African forests. Can you tell us more?

Sylvie Gourlet-Fleury: The current development plans are based on data acquired since 1982 from the M’BaÏKI research site in the Central African Republic, one of the region’s longest-established experimental sites. These data allow the forest dynamics to be evaluated.

One piece of information of interest to everyone is what’s happening beyond the scope of exploitation itself. Forestry companies only exploit certain tree species, and within that, only trees with a trunk caliper over a certain diameter: this is known as commercial stock. What interests us in these projects is how this stock rebuilds itself as successive exploitations occur.

We collect data on several sites in the Congo Basin, and the problem we find on the plots studied is the low density of commercial species. In order to study enough plants, it would be necessary to work on larger areas, but this sort of complete plot inventorying is very costly. The other option is to perform research targeting particular species that can be observed along pathways or routes. As part of the DynAfFor and P3FAC projects, we decided to combine plot and route studies in order to design new, more comprehensive tools.

Jean-Louis Doucet: Our tools allow us to study the dynamics of the forest, its growth, regeneration and the impact of exploitation on the natural dynamic. The work, undertaken with several forestry companies, has enabled us to produce an initial scientific publication synthesizing data on the growth of the main commercial species. We then observed high variability between the sites, but also within the same site: the Central African forests aren’t all the same.

So you have been able to identify different types of forests. What are the main results?

JLD: This project to identify forest types was made possible by working with the private sector, forestry companies that provided essential data. We were able to determine ten main types of forest, each with their own dynamic. But you’d sometimes see several commercial species regenerating slowly, which could compromise sustainable exploitation in the long term.

SGF: We tried to assess the resilience of these ecosystems to future planetary changes, and were able to identify more sensitive areas. However, our resources are limited, and can only cover part of the 10 main forest types we’ve defined. We need much more equipment to take this variability into account.

What recommendations are you putting together for more sustainable forestry development?

JLD: Development plans need to take into account this heterogeneous nature of forest types. The research equipment network needs to be extended to all these forest types.
In addition, one of our recommendations focuses on standardising the minimum exploitable diameter across an entire region. Currently, countries in the region have their own values, but these aren’t always based on the ecological characteristics of the species or on their regenerative abilities.

It’s also necessary, with a few exceptions, to standardise rotations - the interval between two cuts - to 30 years in order to allow the stocks to better recover. And in the second rotation, it’s vital to ensure the stocks have recovered 100% for commercial species as a whole, and at least 50% per species.  

In addition, combating poaching and excessive hunting is essential, because almost 80% of tree species need the animals to disperse the seed.
Finally, to alleviate the lack of regeneration in some species, some enrichments are necessary: for example silviculture, the re-planting of commercial species in the swathes cut by exploitation, or in degraded forest areas.

SGF: Monitoring devices for the forest dynamic need to be installed in all the major concessions. Concessionaires managing over 50,000 hectares need to set up at least one data collection route. That would allow variability in species’ behaviours to be ascertained locally.

How do these projects motivate those involved to buy into these recommendations?

SGF: We’ve prioritised collaboration with the private sector to install the devices, maximising the chances that some concessions will continue to monitor and preserve these sites.

JLD: As regards the implementation of these recommendations, we’re trying to work with national administrations, in the form of scientific councils, while working in partnership with a regional body, the Central Africa Forests Commission (COMIFAC). We’re also working with the International Tropical Timber Technical Association (ATIBT), where we’re both on the scientific council. ATIBT is part of the DYNAFAC collective, which brings together all the bodies investing in the Central African forest monitoring systems.  

SGF: The reality today is that timber stocks that are exploited during one rotation will be diminished in the next. Without changing, without applying these recommendations, these stocks will be unable to properly renew. For now, our interactions with public authorities remain limited, but we hope to lead a project in Gabon which will better involve the forest administration in these considerations.

JLD: Implementing these recommendations will have an economic impact for the forestry companies: as a result we need to find mechanisms that allow those involved in this change to be recompensed. For example, reducing the tax burden on companies that play their part in sustainability, because today they face unfair competition from the informal markets.