| This dissertation explores the causes and consequences of tropical monodominant forests. Monodominant forests are defined as forests in which {dollar}>{dollar}60% of the canopy is comprised of a single tree species. I studied the monodominant Gilbertiodendron dewevrei forest of northeastern Congo.; I performed the first test of the ectomycorrhizal hypothesis for monodominance by surveying the mycorrhizal status of dominant, as well as other common, but not dominant, species in the forest. The survey revealed that two dominant species form both ectomycorrhizae (EM) and vesicular-arbuscular mycorrhizae (VAM), whereas another dominant, forms only vesicular-arbuscular mycorrhizae. These results, along with those of the other species in this forest, demonstrate the relationship between EM and tropical monodominance is complex and show that EM cannot explain all cases of tropical monodominance.; I also tested the hypothesis that dominant species experience an advantage over other plant species because they invest heavily in defenses and suffer relatively less herbivory and pathogen damage when they are seedlings and saplings. I found no support for this hypothesis, as the dominant species in the Congo suffered the heaviest rates of damage.; In addition to the ectomycorrhizal and herbivory hypotheses, I tested for differences in the rates of decomposition, the availability of nitrogen and the amount of light penetration to the understory in both forest types. In all of these cases, there were striking differences between the two forest types with slower decomposition, less nitrogen availability and deeper shade in the Gilbertiodendron forest.; My results suggest that the Gilbertiodendron maintains its dominance by creating an understory environment that is inhospitable to other species. Moreover, saplings of Gilbertiodendron seem well adapted to survive in the understory of the Gilbertiodendron forest and hence, a positive feedback loop is created wherein the juveniles of the dominant species are the only species able to tolerate the stressful environment created by the adult.; In general, all tropical monodominant species share a suite of traits in both the adult and juvenile stages that allow them to establish and maintain dominance. In addition, historical factors affect the ability of a potentially dominant species to achieve dominance. |
