Secondary succession is a complex process involving numerous factors acting across scales. Understanding secondary succession in tropical dry forests is important for the conservation and restoration of this highly threatened biome. My research aims to improve knowledge of the trajectories and drivers of secondary succession in this biome, and the underlying mechanisms. I used a combination of literature synthesis, observational and experimental approaches to study plant-plant interactions and community changes during succession. Through review of published studies, I showed that established trees have a mainly positive effect on the seed dispersal, survival and germination of the subsequent generation of woody plants. However, the balance between positive and negative effects is more complex at the seedling establishment stage and can be influenced by the precipitation regime. Metaanalyses of chronosequence studies showed an increase in tree and shrub species richness with succession and a slow convergence of successional forest species composition with that of old-growth forests. Using survey of young woody plants establishing under isolated trees in pastures, I showed that the attributes of the trees influence the functional composition of the regeneration assemblages but are only weakly related to their taxonomic composition. The position of isolated trees in the landscape is also influential, but this is complex and sitespecific. Through extensive sampling of leaf functional traits of sapling communities in secondary forests of different successional age, I found that community functional composition shifts from conservative towards acquisitive strategies of resource economics, through both species turnover and intraspecific variation of trait values. Five of the measured traits also showed directional changes with tree ontogeny. Lastly, an experimental test of seed fate showed that leaf litter reduced seed removal in successional forests. Seed germination rate was higher in successional forests compared with open sites and generally benefited from the presence of litter. Overall, this research suggests a higher predictability of successional trajectories when studied through functional rather than taxonomic omposition. It also shows heterogeneity in successional trajectories among tropical dry forests that require further study.

Chez les scolytes (Curculionidae : Scolytinae) réalisant des pullulations éruptives, les processus conditionnant l’intensité et la durée des pullulations sont généralement mal connus. Nous avons étudié trois facteurs susceptibles de moduler les pullulations d’Ips sexdentatus (Börner) : la compétition intraspécifique, les ennemis naturels et la température. Les densités de colonisation et le seuil critique de densité d’attaques sur arbres ont été estimés lors d’une pullulation, et les effets de ces densités sur la productivité et la fitness des insectes ont été mesurés en laboratoire. L’entomofaune associée au scolyte a été étudiée dans des peuplements de pins présentant différents niveaux de dégâts de l’insecte. Les effets thermiques ont été estimés via des élevages à différentes températures. Les densités de colonisation sur arbres, ou celle correspondant à la valeur du seuil critique, ont fortement affecté la productivité et la fitness d’I. sexdentatus. L’entomofaune associée était peu sensible aux niveaux de population du scolyte, dont la productivité a cependant été réduite par la durée d’exposition aux ennemis naturels. L’estimation des besoins thermiques de l’espèce a permis de calculer qu’un réchauffement de 1°C augmenterait les effectifs et permettrait l’apparition d’une troisième génération annuelle, tout en réduisant la fitness des insectes. La compétition intraspécifique serait un facteur critique de régulation des pullulations d’I. sexdentatus alors que les ennemis naturels joueraient un rôle plus secondaire. Une élévation de température pourrait aggraver les pullulations mais aussi réduire la fitness des insectes et augmenter la compétition intraspécifique. / For eruptive bark beetles (Curculionidae: Scolytinae), the processes affecting the intensity and duration of outbreaks are generally poorly known. We have investigated three factors that may affect the population dynamics of Ips sexdentatus (Börner), namely the intraspecific competition, the natural enemies and the temperature. Colonization densities and the critical threshold of attack densities on trees have been estimated during an outbreak. How such densities affected the productivity and fitness of the beetles has been evaluated under laboratory conditions. The insect community associated with the bark beetle has been characterized in pine stands exhibiting different damage levels. To assess the thermal effects, the insects have been reared at different temperatures. Colonization densities on trees, or equivalent to the critical threshold of attacks, dramatically affected both the productivity and fitness of I. sexdentatus. The associated fauna was loosely related to the population levels of the bark beetle, although the duration of the exposure to the natural enemies affected its productivity. The assessment of thermal requirements allowed calculating that an average warming of 1°C during the activity period would increase the population levels and number of generations per year, but also decrease the beetles’ fitness. Intraspecific competition is probably a critical regulating factor for I. sexdentatus, while natural enemies would rather play a secondary role. A temperature increase could aggravate the outbreaks, but this could be counterbalanced by a fitness reduction and an increase of intraspecific competition.