Dynamics of Resprouting and Forest Regeneration Following Anthropogenic Land Use in the Central Amazon Basin

Tree mortality is increasing with the effects of climate change and drought across the Amazon Basin while intense fires are becoming more prevalent. Tropical moist forest trees generally lack adaptations that protect against mortality during an intense fire, so anthropogenic burning typically kills high percentages of trees. Following disturbances where prescribed burning is used to limit woody encroachment and to fertilize the soil, abandoned land in central Amazonia becomes dominated by the pioneer tree genus, Vismia. Although the mechanisms by which Vismia comes to dominate previously-burned areas are not known, previous studies on anthropogenic land use and forest succession have hypothesized that the genus possesses a superior ability to resprout after intense fire relative to other tree species. This dissertation examines how Amazonian trees respond to anthropogenic disturbances like clearcutting and slash-and-burn agriculture. Differences in survival and resprouting ability among tree species along the gradient of disturbance severity and across disturbance types can influence the species composition of the regenerating forest community and alter forest structure for decades. Here, we examine the role of resprouting and seeding responses of Vismia species and other tree species common to regenerating tropical moist forests after anthropogenic disturbances, specifically cutting and prescribed fires. We found that species of Cecropia, a tree genus containing neotropical pioneers, along with Vismia, can resprout after losing all or most of their aboveground damage and that Cecropia survived cutting often than Vismia. Although less likely to survive cutting, those Vismia species were more likely than Cecropia to resprout from belowground tissues. As tissues situated belowground are better protected from fires than aboveground tissue, Vismia species may be more likely to survive and resprout following anthropogenic fires. Following a prescribed fire, we found that while several species were eliminated, Vismia species and two additional species common to secondary forests in Neotropical forests resprouted after burning. Vismia species were the only trees, however, that successfully colonized recently-burned areas by resprouting and seeding, whereas other tree species colonized by either seeding or resprouting. Although Vismia can recolonize after fire, post-fire resprouting ability does not fully explain why the genus dominates degraded Amazonian forest. Instead, the combined ability of Vismia species to resprout and seed after fire may explain Vismia persistence through repeated annual fires and the genus’ dominance in the regenerating forest community for decades after abandonment. Finally, we used a long-term survey of forest succession following anthropogenic disturbances to ask whether the occurrence of multi-stemmed individuals relative to single-stemmed trees changes with the number of anthropogenic fires that took place prior to land abandonment. Trees that have multiple stems are likely the product of resprouting after being damaged and we found that several tree species commonly found on abandoned land that was previously burned multiple times were more likely to have multiple stems with increasing fire frequency. This dissertation demonstrates that the mechanisms by which Vismia species come to dominate degraded Amazonian lands is more complex than previously thought. By better understanding how trees in the largest tropical forest on the planet respond to anthropogenic disturbance may help us mitigate the loss of biodiversity in the face of increasing pressure from humans in tropical regions worldwide