The spatio-temporal dynamics of Marantaceae forests in Central Africa

Abstract

Tropical moist forests are currently threatened by global changes, leading to an increase in degraded forest areas. A little-known yet widespread forest type in central Africa, the Marantaceae forests, presents a degraded appearance due to its open canopy and striking lack of tree regeneration caused by a dense understory dominated by giant herbs. These forests are believed to have remained stable for thousands of years, making them a potential example of arrested succession or of alternative stable state. As they appear to thrive under current global changes, it raises significant concerns for the future of central African forests. This thesis aims to investigate the external drivers and ecological mechanisms that explain the persistence and expansion of Marantaceae forests in northern Congo, a hotspot for this unique forest type.I used diverse approaches to explore the dynamics of Marantaceae forests, ranging from landscape scale to tree stand scale, and down to individual scale. First, I combined remote sensing and extensive field data to characterise the distribution and floristic and faunal composition of Marantaceae forests in the Sangha river region. I then focused on the community level to study the post-fire dynamics of these forests and the impact of logging on giant herbs and their reproductive strategy using extensive field inventories, soil and leaf measurements, seed experiments, drone acquisitions and genetic analyses. Finally, I examined the individual interactions between giant herbs and tree saplings in an 11-months nursery experiment to study competitive and potential allelopathic interactions, measuring the leaf and root traits of tree saplings in different treatments.My results show that open Marantaceae forests are significantly associated with drier areas and share a common flora with previously burned secondary forests, supporting the hypothesis of a specific link between Marantaceae forests and fire. I also found that fire had