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University of the Witwatersrand (2021)

The reproductive ecology of the Pepperbark tree (Warburgia salutaris) in the Kruger National Park, South Africa

Van den Bosch, Kaylee

Titre : The reproductive ecology of the Pepperbark tree (Warburgia salutaris) in the Kruger National Park, South Africa

Auteur : Van den Bosch, Kaylee

Université de soutenance : University of the Witwatersrand

Grade : Master of Science (MS) 2021

Résumé partiel
Warburgia salutaris, the pepperbark tree, is an endangered tree that is greatly valued in South Africa for its use in traditional medicine. Over-exploitation for medicinal purposes, habitat degradation and loss have all contributed to the species being listed as IUCN Endangered. In the Kruger National Park (KNP), W. salutaris fruit production is low and only produced on a few trees and there is a very low proportion of juveniles, suggesting that recruitment is extremely limited in this population. Therefore, in this thesis, the reproductive ecology of the KNP population is studied and compared with a reproductively successful orchard population in Eston (KwaZulu-Natal), to investigate factors that may contribute to limited sexual output in the former. The aim of the first part of the study was to understand the pollination biology of W. salutaris. Potential pollinators were observed and collected for further analysis ; nectar volume and sugar concentration were measured ; five pollination treatments – autonomous self-, geitonogamous self-, cross-, natural- and natural-bagged pollination (i.e. naturally pollinated flowers were bagged to protect from seed predation) – were set-up to elucidate the breeding system ; pollen viability was assessed, and pollen tube growth was compared between pollination treatments. The aim of the second part of the study was to understand the seed ecology of W. salutaris. Immature fruit were bagged to assess fruit development in the KNP population and Eston orchard ; fruit were analysed to assess the effect of pre-dispersal seed predation and identify seed predators ; frugivore activity was observed in Leshiba Game and Nature Reserve (GNR), Limpopo, to identify seed dispersers and assess the mode of dispersal ; and seedling emergence trials were conducted to compare seed germination between the natural KNP and Leshiba GNR populations and the Eston orchard. Results showed that W. salutaris flowers are visited by a variety of insects and Lepidoptera (butterflies and moths) are the most likely effective pollinators.

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