Human impacts on how savanna plants interact through fire, resources, and microclimate

Abstract

Grasslands and savannas harbor immense plant biodiversity. This biodiversity is threatened by land transformation. Moreover, the biodiversity of even intact ecosystems is affected by widespread human impacts on environmental factors-- particularly resources, fire, and climate-- that underlie interactions among plant species and structure plant communities. This dissertation examines how plants interact by affecting, and responding to, their environment. Much research has examined how plants interact by depleting shared limiting resources such as nitrogen (i.e., resource competition), and how increasing nitrogen deposition causes biodiversity loss; this research has been mainly north-temperate. To widen understanding of this issue, I examined the roles of multiple nutrients in structuring endemic-rich grasslands of conservation concern on highly weathered soils in South Africa, as part of the globally distributed Nutrient Network experiment. It is less clear how plants interact through fire and microclimate. I investigated how grasses differ from other herbaceous plants (forbs) in their effects on fire behavior and resource availability, and how fire and resources in turn affected savanna tree establishment, in a 16-year biodiversity experiment. I also investigated how plant diversity and composition interacted with experimentally simulated global warming to determine microclimate and resource availability, and how microclimate and resource availability in turn affected seedling establishment of 32 savanna herb and tree species. This research on the multiple ways in which plants interact by influencing their environment sheds light on how human actions alter grassland and savanna biodiversity.