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The invasion process of Cecropia peltata in Cameroon and its impact on the native species Musanga cecropioides

par Baudoux, Claire
Président du jury Noret, Nausicaa
Promoteur Hardy, Olivier J.
Co-Promoteur Heuret, Patrick
Publication Non publié, 2025-12-10

Thèse de doctorat

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Résumé :

Biological invasions are among the main drivers of global biodiversity change, yet their study in tropical Africa remains limited. This thesis investigates the invasion process and ecological impacts of Cecropia peltata L. (Urticaceae), a fast-growing Neotropical pioneer tree that has become invasive in Cameroon, where it appears to be progressively replacing the closely related native species Musanga cecropioides R.Br. ex Tedlie. Through complementary approaches combining field surveys, architectural analysis, and experimental trials, this work explores the spatial dynamics, ecological mechanisms, and biological traits underlying this invasion.In the first part of this work, the geographical distribution and temporal progression of C. peltata across southern Cameroon is assessed. Roadside surveys revealed its widespread establishment in the Littoral and South-West regions, extending over approximately 15,000 km², with a clear decline in abundance away from the presumed introduction site at Limbe Botanical Garden. Historical comparisons showed an eastward expansion of about 143 km over the past century and a concomitant decline in M. cecropioides abundance, suggesting a process of competitive replacement.Second, a retrospective morphological approach to reconstruct past invasion dynamics and quantify performance differences between the two species was tested and validated. By analysing tree architecture and reproductive traits, we found that C. peltata exhibits faster early growth and earlier reproductive maturity than its native counterpart. These traits likely confer this non-native species a competitive advantage over M. cecropioides as well as an advantage in disturbed environments, where rapid colonization and reproduction is key to persistence.Finally, controlled germination and growth experiments demonstrated that although both species have high germination success, C. peltata germinates faster, grows more rapidly during early development, and suffers lower mortality over time in our controlled outdoor experiment. While no direct allelopathic effects were detected, the native M. cecropioides appeared more vulnerable to biotic stress, possibly supporting the enemy release hypothesis.Overall, this thesis provides a comprehensive analysis of the invasion process of C. peltata in Cameroon, shedding light on its invasion history and the mechanisms that likely contribute to its ecological success. These findings add to our understanding of biological invasions in tropical ecosystems and may help inform future considerations for managing woody invaders in African landscapes.