Invasive potential of the Peruvian pepper tree (Schinus molle) in South Africa

[摘要] ENGLISH ABSTRACT: Natural and semi-natural ecosystems and human communities worldwide are under siegefrom a growing number of destructive invasive alien species. Alien species are thosewhose presence in an area is due to intentional or accidental introduction as a result ofhuman activities. Some alien species become invasive, and some cause tremendousdestruction to the ecosystem and their stability, but we do not yet understand fully themany factors that determine the levels of invasiveness in alien species. However,management of alien plants requires a detailed understanding of the factors that makethem invasive in their new habitat. The aim of this study was to explore in detail theprocesses and potential for invasion of Schinus molle (Peruvian pepper tree) into semiaridsavanna in South Africa and to examine the potential for this species to invadefurther in these ecosystems, and in other South African biomes.In this thesis I explored the patterns and processes of invasion of S. molle in semiaridsavanna using small-scale experiments to investigate physical and ecological barriersto invasion that prevent or accelerate the invasion of this species. I examined factors suchas pollination; seed production; seed dispersal; seed predation and viability, all known tocontribute to invasiveness. I highlighted the critical role of microsite conditions(temperature, humidity, water availability) in facilitating S. molle seedling establishmentin semi-arid savanna and demonstrated that microsite type characteristics need to beconsidered for management and monitoring of the species in South Africa. Idemonstrated the ability of S. molle to out-compete indigenous woody plants for light andother resources and also showed that disturbance of natural ecosystems was not aprerequisite for invasion, although human activities such as tree planting have played amajor role in disseminating this species in South Africa.Predicting the future distribution of invasive species is very important for themanagement and conservation of natural ecosystems, and for the development of policy.For this reason, I also assessed the present and potential future spatial distribution of S.molle in South Africa by using bioclimatic models and a simulation-based spread model.I produced accurate profiles of environmental conditions (both biophysical and those related to human activities) that characterize the planted and naturalized ranges of thisspecies in South Africa, by linking species determinants, potential habitat suitability andlikely spread dynamics under different scenarios of management and climate change. Allthose components provided insights on the dynamics of invasions by fleshy-fruitedwoody alien plants in general, and on S. molle invasions in South Africa in particular. Ideveloped a conceptual model that described S. molle population dynamics leading to anunderstanding of the processes leading to the invasive spread of this species in SouthAfrica. This work also emphasized the need for policy review concerning the invasivestatus of S. molle in South Africa, and recommendations are made for future research.

[发布机构] Stellenbosch University