Doctor of Philosophy (PhD)
As anthropogenic forests become more common in the tropics, there is a greater need to understand the factors that impact forest succession. I used censuses of woody plants in successional forests to study the effects of prior land use and tree plantations on species composition and richness. First, I tested the hypothesis that communities originating from different land uses were converging in species composition over time. I compared species composition using the Chao-Jaccard similarity index. I observed shifts in the dominant species during the first 30 years of succession, but not convergence of species composition in sites with different land-use history. Initial floristics appeared to have a large impact on later successional stages. Areas with more intense land use exhibited lower ecosystem resilience. Second, I tested the hypothesis that monoculture tree plantations with light management had higher species richness and a later-successional species composition than secondary forests of similar ages. To describe species composition, I used ordination techniques, classification of species into different functional groups, and calculation of several community-weighted functional traits. Species richness of woody plants was similar in these two forest types during the second decade of succession, but species composition was shifted from early- to mid-successional species in tree plantations relative to secondary forests. Tree plantations had a higher community-weighted seed mass, and a lower abundance of shrubs and bat-dispersed species than secondary forests. However, abundance of mature forest species and community-weighted wood density and leaf mass area did not differ between forests types. Third, I asked whether tree plantations and secondary forests became more similar over time and whether the rate of change in various vegetation characteristics differed between these two forest types. Stem density and basal area of tree plantations became more similar to secondary forests over the course of three years. However, rates of change in species richness, functional groups, and functional traits did not differ between forest types. Species composition was not converging. I concluded that these types of tree plantations marginally catalyze the recovery of species composition compared to secondary forests.
Longworth, John Benjamin, "The Effects of Tree Plantations and Land Use on Natural Regeneration of Woody Plants in the Tropics: Diversity, Species Composition, Successional Dynamics, and Functional Traits" (2018). LSU Doctoral Dissertations. 4190.