Date of Award
Doctor of Philosophy (PhD)
Schnitzer, Stefan A.
Succession is a fundamental process in ecology in which ecosystems recover after disturbances. The goal of the study of ecological succession is to understand the mechanisms responsible for changes in species’ density, diversity, and ecosystem processes. Understanding the mechanisms that determine how young tropical forests change during succession is crucial because approximately half of the world’s tropical forests are regenerating after farmland abandonment, and successional forests are now expected to supply the vast majority of ecosystems services that were provided by old growth forests (e.g. carbon sequestration). Edaphic factors, initial conditions, and competition have been proposed to be key drivers that influence tropical forest succession; however, how these drivers alter succession remains poorly understood. For my doctoral dissertation research, I used census data from a young tropical dry forest, and a large-scale field experiment in a tropical moist forest to examine the combined effects of edaphic factors and initial conditions on forest succession, as well as the effect of lianas on trees, an intense form of plant competition, on forest succession.In the dry forest, edaphic factors and initial conditions were strong determinants of succession. Soil fertility accelerated tree biomass accretion. Topography made liana composition more similar over time. Initial conditions decreased sapling recruitment and biomass accretion, probably due to lower light levels when there is more basal area early in succession. The accumulation of tree species was slowed while tree composition similarity increased with more basal area early in succession. Competition for space may have delayed tree recruitment in the canopy and homogenized composition. In the moist forest, liana competition significantly influenced succession. Lianas contributed 20% of the foliage to the forest canopy, and thus significantly reduced light level and tree biomass accumulation. Lianas reduced tree biomass accumulation even when trees received full sunlight and their canopies were intact. Finally, using a comprehensive literature review on liana removal experiments, I report that lianas decrease tree establishment, growth, biomass accumulation and reproduction across the world’s tropical forests. In summary, liana competition, edaphic factors, and initial conditions all influence the rate and direction of succession in young tropical forests.
Available for download on Friday, April 10, 2020