Dynamics, diversity patterns, and disturbances of multiple life stages of tropical trees

Global biodiversity loss is accelerated by the pervasive loss and degradation of tropical forests. What maintains the immense but imperilled diversity of tropical forests remains a principal question in ecology. Efforts to conserve tropical species could be strengthened by a more detailed understanding of how anthropogenic disturbances impact forest diversity and dynamics, including the mechanisms that maintain and structure diverse plant communities. In this thesis, I first examine the contributions of fungal pathogens, as specialist natural enemies, in driving diversity enhancement in Borneo’s mast fruiting forests. Using a manipulative shadehouse experiment, I demonstrate that fungal pathogens are responsible for weak conspecific density-dependent mortality, that is unlikely to promote overall diversity in this mast fruiting system. I then review recent modelling approaches explaining tropical plant diversity and highlight that the effectiveness of coexistence mechanisms is sensitive to species’ demographic variations and dispersal ability. Next, I explore how tropical selective logging affects the composition of multiple life stages of Borneo’s diverse tree assemblages. I find persistent patterns of high spatial turnover in tree communities of all life stages 12 years after two successive logging rotations. Turnover is the result of greater dispersal limitations from increasingly isolated and aggregated adult trees as opposed to increased environmental heterogeneity after logging. Finally, I consider the impacts of liana (woody-vine) proliferation on patterns of tree functional trait similarity following logging. Combining freely available plant functional trait data with local tree community and liana infestation data, I find that local-scale patterns of liana infestation do not strongly relate to the simplification of host tree functional composition after harvests. Collectively, my results suggest that selective logging causes long-term modifications to tree communities with the potential to severely disrupt the still largely unknown mechanisms and drivers of tropical diversity enhancement. To reduce the impacts of future degradation on the diversity and dynamics of logged tropical forests there is a need to foster sustainable forestry and forest restoration practices, and consider more widely how diversity is maintained, to infer how it can be conserved.